'> '> ]> xproc 2008-11-26 XML Revision markup Norman Walsh Mark Logic Corporation norman.walsh@marklogic.com Alex Milowski Invited expert alex@milowski.org Henry S. Thompson University of Edinburgh ht@inf.ed.ac.uk This specification describes the syntax and semantics of XProc: An XML Pipeline Language, a language for describing operations to be performed on XML documents. An XML Pipeline specifies a sequence of operations to be performed on zero or more XML documents. Pipelines generally accept zero or more XML documents as input and produce zero or more XML documents as output. Pipelines are made up of simple steps which perform atomic operations on XML documents and constructs similar to conditionals, iteration, and exception handlers which control which steps are executed. This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/. This document was produced by the XML Processing Model Working Group which is part of the XML Activity. Publication as a Candidate Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress. This is a Candidate Recommendation of XProc: An XML Pipeline Language. The Working Group believes that this specification sufficiently addresses the use cases and requirements that it set out to address (). The Last Call Working Draft of this specification resulted in a number of comments which have all been addressed by the Working Group. The Last Call comments and their disposition are summarized in our Disposition of Comments document. The changes made between Last Call and this Candidate Recommendation draft are highlighted in a draft with revision markup. The W3C publishes a Candidate Recommendation to indicate that the document is believed to be stable and to encourage implementation by the developer community. A test suite with coverage of the primary XProc constructs has been created. The Working Group expects to request that the Director advance this document to Proposed Recommendation once the Working Group has completed the test suite and demonstrated at least two interoperable implementations for each test. Based on known implementations, the Working Group does not plan to request to advance to Proposed Recommendation prior to 01 February 2009. An ongoing implementation report will be maintained. Please send comments about this document to public-xml-processing-model-comments@w3.org (public archives are available). This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

An XML Pipeline specifies a sequence of operations to be performed on a collection of XML input documents. Pipelines take zero or more XML documents as their input and produce zero or more XML documents as their output. A pipeline consists of steps. Like pipelines, steps take zero or more XML documents as their inputs and produce zero or more XML documents as their outputs. The inputs of a step come from the web, from the pipeline document, from the inputs to the pipeline itself, or from the outputs of other steps in the pipeline. The outputs from a step are consumed by other steps, are outputs of the pipeline as a whole, or are discarded. There are three kinds of steps: atomic steps, compound steps, and multi-container steps. Atomic steps carry out single operations and have no substructure as far as the pipeline is concerned. Compound steps and multi-container steps control the execution of other steps, which they include in the form of one or more subpipelines. This specification defines a standard library, , of steps. Pipeline implementations may support additional types of steps as well. is a graphical representation of a simple pipeline that performs XInclude processing and validation on a document.

A simple, linear XInclude/Validate pipeline

This is a pipeline that consists of two atomic steps, XInclude and Validate with XML Schema. The pipeline itself has two inputs, “source” (a source document) and “schemas” (a sequence of W3C XML Schemas). The XInclude step reads the pipeline input “source” and produces a result document. The Validate with XML Schema step reads the pipeline input “schemas” and the result of the XInclude step and produces its own result document. The result of the validation, “result”, is the result of the pipeline. (For consistency across the step vocabulary, the standard input is usually named “source” and and the standard output is usually named “result”.) The pipeline document determines how the steps are connected together inside the pipeline, that is, how the output of one step becomes the input of another. The pipeline document for this pipeline is shown in . <p:declare-step xmlns:p="http://www.w3.org/ns/xproc" name="xinclude-and-validate"> <p:input port="source" primary="true"/> <p:input port="schemas" sequence="true"/> <p:output port="result"> <p:pipe step="validated" port="result"/> </p:output> <p:xinclude name="included"> <p:input port="source"> <p:pipe step="xinclude-and-validate" port="source"/> </p:input> </p:xinclude> <p:validate-with-xml-schema name="validated"> <p:input port="source"> <p:pipe step="included" port="result"/> </p:input> <p:input port="schema"> <p:pipe step="xinclude-and-validate" port="schemas"/> </p:input> </p:validate-with-xml-schema> </p:declare-step> The example in is very verbose. It makes all of the connections seen in the figure explicit. In practice, pipelines do not have to be this verbose. XProc supports defaults for many common cases: If you use p:pipeline instead of p:declare-step, the “source” input port and “result” output port are implicitly declared for you. Where inputs and outputs are connected between sequential sibling steps, they do not have to be made explicit. The same pipeline, using XProc defaults, is shown in . <p:pipeline xmlns:p="http://www.w3.org/ns/xproc" name="xinclude-and-validate"> <p:input port="schemas" sequence="true"/> <p:xinclude/> <p:validate-with-xml-schema> <p:input port="schema"> <p:pipe step="xinclude-and-validate" port="schemas"/> </p:input> </p:validate-with-xml-schema> </p:pipeline> is a more complex example: it performs schema validation with an appropriate schema and then styles the validated document.

A validate and transform pipeline

The heart of this example is the conditional. The “choose” step evaluates an XPath expression over a test document. Based on the result of that expression, one or another branch is run. In this example, each branch consists of a single validate step. <p:pipeline xmlns:p="http://www.w3.org/ns/xproc"> <p:choose> <p:when test="/*[@version &lt; 2.0]"> <p:validate-with-xml-schema> <p:input port="schema"> <p:document href="v1schema.xsd"/> </p:input> </p:validate-with-xml-schema> </p:when> <p:otherwise> <p:validate-with-xml-schema> <p:input port="schema"> <p:document href="v2schema.xsd"/> </p:input> </p:validate-with-xml-schema> </p:otherwise> </p:choose> <p:xslt> <p:input port="stylesheet"> <p:document href="stylesheet.xsl"/> </p:input> </p:xslt> </p:pipeline> This example, like the preceding, relies on XProc defaults for simplicity. It is always valid to write the fully explicit form if you prefer. The media type for pipeline documents is application/xml. Often, pipeline documents are identified by the extension .xpl. In this specification the words must, must not, should, should not, may and recommended are to be interpreted as described in .

A pipeline is a set of connected steps, with outputs of one step flowing into inputs of another. A pipeline is itself a step and must satisfy the constraints on steps. Connections between steps occur where the input of one step is bound to the output of another. The result of evaluating a pipeline (or subpipeline) is the result of evaluating the steps that it contains, in an order consistent with the connections between them. A pipeline must behave as if it evaluated each step each time it occurs. Unless otherwise indicated, implementations must not assume that steps are functional (that is, that their outputs depend only on their inputs, options, and parameters) or side-effect free. The pattern of connections between steps will not always completely determine their order of evaluation. The evaluation order of steps not connected to one another is implementation-dependent.

A step is the basic computational unit of a pipeline. A typical step has zero or more inputs, from which it receives XML documents to process, zero or more outputs, to which it sends XML document results, and can have options and/or parameters. There are three kinds of steps: atomic, compound, and multi-container. An atomic step is a step that performs a unit of XML processing, such as XInclude or transformation, and has no internal subpipeline. Atomic steps carry out fundamental XML operations and can perform arbitrary amounts of computation, but they are indivisible. An XSLT step, for example, performs XSLT processing; a Validate with XML Schema step validates one input with respect to some set of XML Schemas, etc. There are many types of atomic steps. The standard library of atomic steps is described in , but implementations may provide others as well. It is implementation-defined what additional step types, if any, are provided. Each use, or instance, of an atomic step invokes the processing defined by that type of step. A pipeline may contain instances of many types of steps and many instances of the same type of step. Compound steps, on the other hand, control and organize the flow of documents through a pipeline, reconstructing familiar programming language functionality such as conditionals, iterators and exception handling. They contain other steps, whose evaluation they control. A compound step is a step that contains a subpipeline. That is, a compound step differs from an atomic step in that its semantics are at least partially determined by the steps that it contains. Finally, there are two “multi-container steps”: p:choose and p:try. A multi-container step is a step that contains several alternate subpipelines. Each subpipeline is identified by a non-step wrapper element: p:when and p:otherwise in the case of p:choose, p:group and p:catch in the case of p:try. The runtime semantics of a multi-container step are that it behaves as if it evaluated exactly one of its subpipelines. In this sense, they function like compound steps. A compound step or multi-container step is a container for the steps directly within it or within non-step wrappers directly within it. The steps that occur directly within, or within non-step wrappers directly within, a step are called that step's contained steps. In other words, “container” and “contained steps” are inverse relationships. The ancestors of a step, if it has any, are its container and the ancestors of its container. Sibling steps (and the connections between them) form a subpipeline. The last step in a subpipeline is its last step in document order. subpipeline = p:variable*, (p:for-each|p:viewport|p:choose|p:group|p:try|p:standard-step|pfx:user-pipeline)+ User-defined pipelines (identified with pfx:user-pipeline in the preceding syntax summary) are atomic. A pipeline declaration may contain a subpipeline, but the invocation of that pipeline does not. Steps have “ports” into which inputs and outputs are connected or “bound”. Each step has a number of input ports and a number of output ports; a step can have zero input ports and/or zero output ports. (All steps have an implicit output port for reporting errors that must not be declared.) The names of all ports on each step must be unique on that step (you can't have two input ports named “source”, nor can you have an input port named “schema” and an output port named “schema”). A Step may have zero or more options, all with unique names. Steps may have parameter input ports, on which parameters can be passed. Only one parameter with any given name can be passed to a step. If multiple parameters with the same name are used, only one of the values will actually be available to the step. A step can have zero, one, or many parameter input ports, and each parameter port can have zero or more parameters passed on it. All of the different instances of steps (atomic or compound) in a pipeline can be distinguished from one another by name. If the pipeline author does not provide a name for a step, a default name is manufactured automatically.

The name attribute on any step can be used to give it a name. The name must be unique within its scope, see . If the pipeline author does not provide an explicit name, the processor manufactures a default name. All default names are of the form “!1.m.n…” where “m” is the position (in the sense of counting sibling elements) of the step's highest ancestor element within the pipeline document or library which contains it, “n” is the position of the next-highest ancestor, and so on, including both steps and non-step wrappers. For example, consider the pipeline in . The p:pipeline step has no name, so it gets the default name “!1”; the p:choose gets the name “!1.2”; the first p:when gets the name “!1.2.1”, etc. If the p:choose had had a name, it would not have received a default name, but it would still have been counted and its first p:when would still have been “!1.2.1”. Providing every step in the pipeline with an interoperable name has several benefits: It allows implementors to refer to all steps in an interoperable fashion, for example, in error messages. Pragmatically, we say that readable ports are identified by a step name/port name pair. By manufacturing names for otherwise anonymous steps, we include implicit bindings without changing our model. In a valid pipeline that runs successfully to completion, the manufactured names aren't visible (except perhaps in debugging or logging output). The format for defaulted names does not conform to the requirements of an NCName. This is an explicit design decision; it prevents pipelines from using the defaulted names on p:pipe elements. If an explicit connection is required, the pipeline author must provide an explicit name for the step.

Although some steps can read and write non-XML resources, what flows between steps through input ports and output ports are exclusively XML documents or sequences of XML documents. For the purposes of this specification, an XML document is an . Implementations are free to transmit Infosets as sequences of characters, sequences of events, object models, or any other representation that preserves the necessary Infoset properties (see ). Most steps in this specification manipulate XML documents, or portions of XML documents. In these cases, we speak of changing elements, attributes, or nodes without prejudice to the actual representation used by an implementation. An implementation may make it possible for a step to produce non-XML output (through channels other than a named output port)—for example, writing a PDF document to a URI—but that output cannot flow through the pipeline. Similarly, one can imagine a step that takes no pipeline inputs, reads a non-XML file from a URI, and produces an XML output. But the non-XML data cannot arrive on an input port to a step. It is a dynamic error if a non-XML resource is produced on a step output or arrives on a step input. The common case is that each step has one or more inputs and one or more outputs. illustrates symbolically an atomic step with two inputs and one output.

An atomic step with two inputs and one output

All atomic steps are defined by a p:declare-step. The declaration of an atomic step type defines the input ports, output ports, and options of all steps of that type. For example, every p:validate-with-xml-schema step has two inputs, named “source” and “schema”, one output named “result”, and the same set of options. Like atomic steps, top level, user-defined pipelines also have declarations. The situation is slightly more complicated for the other compound steps because they don't have separate declarations; each instance of the compound step serves as its own declaration. On these compound steps, the number and names of the outputs can be different on each instance of the step. illustrates symbolically a compound step with one subpipeline and one output. As you can see from the diagram, the output from the compound step comes from one of the outputs of the subpipeline within the step.

A compound step with two inputs and one output

The input ports declared on a step are its declared inputs. The output ports declared on a step are its declared outputs. When a step is used in a pipeline, it is connected to other steps through its inputs and outputs. When a step is used, all of the declared inputs of the step must be connected. Each input can be connected to: The output port of some other step. A fixed, inline document or sequence of documents. A document read from a URI. One of the inputs declared on one of its ancestors. A special port provided by an ancestor compound step, for example, “current” in a p:for-each or p:viewport. When an input accepts a sequence of documents, the documents can come from any combination of these locations. The declared outputs of a step may be connected to: The input port of some other step. One of the outputs declared on its container. The primary output port of a step must be connected, but other outputs can remain unconnected. Any documents produced on an unconnected output port are discarded. Primary input and primary output ports may be implicitly connected if no explicit connection is given, see . Output ports on compound steps have a dual nature: from the perspective of the compound step's siblings, its outputs are just ordinary outputs and must be connected as described above. From the perspective of the subpipeline inside the compound step, they are inputs into which something must be connected. Within a compound step, the declared outputs of the step can be connected to: The output port of some contained step. A fixed, inline document or sequence of documents. A document read from a URI. Each input and output is declared to accept or produce either a single document or a sequence of documents. It is not an error to connect a port that is declared to produce a sequence of documents to a port that is declared to accept only a single document. It is, however, an error if the former step actually produces more than one document at run time. It is also not an error to connect a port that is declared to produce a single document to a port that is declared to accept a sequence. A single document is the same as a sequence of one document. An output port may be connected to more than one input port. At runtime this will result in distinct copies of the output. The signature of a step is the set of inputs, outputs, and options that it is declared to accept. The declaration for a step provides a fixed signature which all its instances share. A step matches its signature if and only if it specifies an input for each declared input, it specifies no inputs that are not declared, it specifies an option for each option that is declared to be required, and it specifies no options that are not declared. In other words, every input and required option must be specified and only inputs and options that are declared may be specified. Options that aren't required do not have to be specified. Steps may also produce error, warning, and informative messages. These messages are captured and provided on the error port inside of a p:catch. Outside of a try/catch, the disposition of error messages is implementation-dependent. How inputs are connected to XML documents outside the pipeline is implementation-defined. How pipeline outputs are connected to XML documents outside the pipeline is implementation-defined.

It's common for some of the documents used in processing a pipeline to be read from URIs. Sometimes this occurs directly, for example with a p:document element. Sometimes it occurs indirectly, for example if an implementation allows the URI of a pipeline input to be specified on the command line or if an p:xslt step encounters an xsl:import in the stylesheet that it is processing. It's also common for some of the documents produced in processing a pipeline to be written to locations which have, or at least could have, a URI. The process of dereferencing a URI to retrieve a document is often more interesting than it seems at first. On the web, it may involve caches, proxies, and various forms of indirection. Resolving a URI locally may involve resolvers of various sorts and possibly appeal to implementation-dependent mechanisms such as catalog files. In XProc, the situation is made even more interesting by the fact that many intermediate results produced by steps in the pipeline have base URIs. Whether (and when and how) or not the intermediate results that pass between steps are ever written to a filesystem is implementation-dependent. In Version 1.0 of XProc, how (or if) implementers provide local resolution mechanisms and how (or if) they provide access to intermediate results by URI is implementation-defined. Version 1.0 of XProc does not require implementations to guarantee that multiple attempts to dereference the same URI always produce consistent results. On the one hand, this is a somewhat unsatisfying state of affairs because it leaves room for interoperability problems. On the other, it is not expected to cause such problems very often in practice. If these problems arise in practice, implementers are encouraged to use the existing extension mechanisms to give users the control needed to circumvent them. Should such mechanisms become widespread, a standard mechanism could be added in some future version of the language.

XProc is designed to allow pipeline authors to specify how an XML document, or sequence of XML documents, flows through a series of steps. For the most part, non-XML documents are considered out-of-scope. However, to be useful, XProc pipelines must interact with the real world where non-XML documents (HTML documents, raster images, non-XML encodings of data, etc.) are a fact of life. Accordingly, some pipelines may need to access non-XML documents and some non-XML documents may “leak” into pipelines. XProc provides a limited set of tools for processing these documents. In particular, XProc offers the ability to turn some “almost-XML” documents into XML and to allow some non-XML documents to flow quietly through the pipeline. It is not a goal of XProc that it should be a general-purpose pipeline language for manipulating arbitrary, non-XML resources. There are two standard ways that a non-XML document may enter a pipeline: directly through p:data or as the result of performing an p:http-request step. Loading non-XML data with a computed URI requires the p:http-request step. Implementors are encouraged to support the file: URI scheme so that users can load local data from computed URIs. In either case, non-XML documents are converted into text or are base64-encoded, depending on their content type and character encoding. The result is an XML document that consists of a document element containing either escaped text or base64-encoded text. This document can be processed like any other XML document. The p:unescape-markup step can be used to (attempt to) convert a non-XML document into XML. Well-formed XML that just happens to be represented with escaped markup can always be recovered. For other media types, the ability to construct XML and the precise mechanisms used to make the markup well-formed are implementation-defined. XProc provides no standard means to save encoded data in its unencoded binary form. Implementors may provide extension methods to allow the p:store step to save the binary data. For example, an implementation might provide a ext:binary serialization method that decoded base64 encoded data before saving it: BASE64ENCODEDDATA ]]>

As a convenience for pipeline authors, each step may have one input port designated as the primary input port and one output port designated as the primary output port. If a step has a document input port which is explicitly marked “primary='true'”, or if it has exactly one document input port and that port is not explicitly marked “primary='false'”, then that input port is the primary input port of the step. If a step has a single input port and that port is explicitly marked “primary='false'”, or if a step has more than one input port and none is explicitly marked as the primary, then the primary input port of that step is undefined. A step can have at most one primary input port. If a step has a document output port which is explicitly marked “primary='true'”, or if it has exactly one document output port and that port is not explicitly marked “primary='false'”, then that output port is the primary output port of the step. If a step has a single output port and that port is explicitly marked “primary='false'”, or if a step has more than one output port and none is explicitly marked as the primary, then the primary output port of that step is undefined. A step can have at most one primary output port. The special significance of primary input and output ports is that they are connected automatically by the processor if no explicit binding is given. Generally speaking, if two steps appear sequentially in a subpipeline, then the primary output of the first step will automatically be connected to the primary input of the second. Additionally, if a compound step has no declared outputs and the last step in its subpipeline has an unbound primary output, then an implicit primary output port will be added to the compound step (and consequently the last step's primary output will be bound to it). This implicit output port has no name. It inherits the sequence property of the port bound to it.

Steps are connected together by their input ports and output ports. It is a static error if there are any loops in the connections between steps: no step can be connected to itself nor can there be any sequence of connections through other steps that leads back to itself.

XProc processors are expected, and sometimes required, to perform namespace fixup. Unless the semantics of a step explicitly says otherwise: The in-scope namespaces associated with a node (even those that are inherited from namespace bindings that appear among its ancestors in the document in which it appears initially) are assumed to travel with that node. Changes to one part of a tree (wrapping or unwrapping a node or renaming an element, for example) do not change the in-scope namespaces associated with the descendants of the node so changed. As a result, some steps can produce XML documents which have no direct serialization (because they include nodes with conflicting or missing namespace declarations, for example). To produce a serializable XML document, the XProc processor must sometimes add additional namespace nodes, perhaps even renaming prefixes, to satisfy the constraints of Namespaces in XML. This process is referred to as namespace fixup. Implementors are encouraged to perform namespace fixup before passing documents between steps, but they are not required to do so. Conversely, an implementation which does serialize between steps and therefore must perform such fixups, or reject documents that cannot be serialized, is also conformant. Except where the semantics of a step explicitly require changes, processors are required to preserve the information in the documents and fragments they manipulate. In particular, the information corresponding to the properties attributes, base URI, children, local name, namespace name, normalized value, owner, and parent must be preserved. The information corresponding to prefix, in-scope namespaces, namespace attributes, and attribute type should be preserved, with changes to the first three only as required for namespace fixup. In particular, processors are encouraged to take account of prefix information in creating new namespace bindings, to minimize negative impact on prefixed names in content. Except for cases which are specifically called out in , the extent to which namespace fixup, and other checks for outputs which cannot be serialized, are performed on intermediate outputs is implementation-defined. Whenever an implementation serializes pipeline contents, for example for pipeline outputs, logging, or as part of steps such as p:store or p:http-request, it is a dynamic error if that serialization could not be done so as to produce a document which is both well-formed and namespace-well-formed, as specified in XML and Namespaces in XML, regardless of what serialization method, if any, is called for.

The environment is a context-dependent collection of information available within sub-pipelines. Most of the information in the environment is static and can be computed for each subpipeline before evaluation of the pipeline as a whole begins. The in-scope bindings have to be calculated as the pipeline is being evaluated. The environment consists of: A set of readable ports. The readable ports are a set of step name/port name pairs. Inputs and outputs can only be connected to readable ports. A default readable port. The default readable port, which may be undefined, is a specific step name/port name pair from the set of readable ports. A set of in-scope bindings. The in-scope bindings are a set of name-value pairs, based on option and variable bindings. The empty environment contains no readable ports, an undefined default readable port and no in-scope bindings. Unless otherwise specified, the environment of a contained step is its inherited environment. The inherited environment of a contained step is an environment that is the same as the environment of its container with the standard modifications. The standard modifications made to an inherited environment are: The declared inputs of the container are added to the readable ports. In other words, contained steps can see the inputs to their container. The union of all the declared outputs of all of the containers's contained steps are added to the readable ports. In other words, sibling steps can see each other's outputs in addition to the outputs visible to their container. If there is a preceding sibling step element: If that preceding sibling has a primary output port, then that output port becomes the default readable port. Otherwise, the default readable port is undefined. If there is not a preceding sibling step element: If the container has a primary input port, the default readable port is that primary input port. Otherwise, the default readable port is unchanged. The names and values from each p:variable present at the beginning of the container are added, in document order, to the in-scope bindings. A new binding replaces an old binding with the same name. See for the specification of variable evaluation. A step with no parent inherits the empty environment.

XProc uses XPath as an expression language. XPath expressions are evaluated by the XProc processor in several places: on compound steps, to compute the default values of options and the values of variables; on atomic steps, to compute the actual values of options and the values of parameters. XPath expressions are also passed to some steps. These expressions are evaluated by the implementations of the individual steps. This distinction can be seen in the following example: <p:variable name="home" select="'http://example.com/docs'"/> <p:load name="read-from-home"> <p:with-option name="href" select="concat($home,'/document.xml')"/> </p:load> <p:split-sequence name="select-chapters" test="@role='chapter'"> <p:input port="source" select="//section"/> </p:split-sequence> The select expression on the variable “home” is evaluated by the XProc processor. The value of the variable is “http://example.com/docs”. The href option of the p:load step is evaluated by the XProc processor. The actual href option received by the step is simply the string literal “http://example.com/docs/document.xml”. (The select expression on the source input of the p:split-sequence step is also evaluated by the XProc processor.) The XPath expression “@role='chapter'” is passed literally to the test option on the p:split-sequence step. That's because the nature of the p:split-sequence is that it evaluates the expression. Only some options on some steps expect XPath expressions. The XProc processor evaluates all of the XPath expressions in select attributes on variables, options, parameters, and inputs, in match attributes on p:viewport, and in test attributes on p:when steps. An XProc implementation can use either or to evaluate these expressions. Allowing either XPath 1.0 or XPath 2.0 is a compromise driven entirely by the timing of XProc development. During the development of this specification, the community indicated that it was too early to mandate that all implementations use XPath 2.0 and too late to mandate that all implementations use XPath 1.0. Many, many expressions that are likely to be used in XProc pipelines are the same in both versions (simple element tests, ancestor and descendant tests, string-based attribute tests, etc.). As an aid to interoperability, pipeline authors may indicate the version of XPath that they are using. The attribute xpath-version may be used on p:pipeline, p:declare-step, or p:library to identify the XPath version that must be used to evaluate XPath expressions on the pipeline(s). The attribute is lexically scoped, but see below. If an xpath-version is specified on a p:pipeline or p:declare-step, then that is the version of XPath that the step uses. If it does not specify a version, but a version is specified on one of its ancestors, the nearest ancestor version specified is the version that it uses. An xpath-version attribute on a p:library specifies a default version for all steps defined in that library. If no version is specified on the step or among its ancestors, then its XPath version is implementation-defined. The decision about which XPath version applies can be made dynamically. For example, if a pipeline explicitly labeled with xpath-version “1.0” imports a library that does not specify a version, the implementation may elect to make the implementation-defined XPath version of the steps in the library also “1.0”. If the same implementation imports that library into a pipeline explicitly labeled with xpath-version “2.0”, it can make the implementation-defined version of those steps “2.0”. The following rules determine how the indicated version and the implementation's actual version interact: If the indicated version and the implementation version are the same, then that version is used. If the indicated version is 1.0 and the implementation uses XPath 2.0 (or later), the expression must be evaluated in XPath 1.0 compatibility mode. It is a dynamic error if a 2.0 processor encounters an XPath 1.0 expression and it does not support XPath 1.0 compatibility mode. Otherwise: It is a dynamic error if the processor encounters an xpath-version that it does not support. XProc processors divide naturally into two classes: XPath 1.0 processors and XPath 2.0 processors. Irrespective of which version of XPath is used, all expressions evaluated by XProc or passed to steps for evaluation must be valid XPath expressions. It is a dynamic error if an XPath expression is encountered which cannot be evaluated (because it is syntactically incorrect, contains references to unbound variables or unknown functions, or for any other reason).

XProc processors that support only XPath 1.0 do not support any types (or features) beyond those described in . They use the XPath 1.0 data model. Processors must implement all of the XPath 1.0 functions, but are not expect to implement the functions described in .

When the XProc processor evaluates an XPath expression using XPath 1.0, unless otherwise indicated by a particular step, it does so with the following initial context: context node The document node of a document. The document is either specified with a binding or is taken from the default readable port. It is a dynamic error if a document sequence appears where a document to be used as the context node is expected. If there is no binding and there is no default readable port then the context node is an empty document node. context position and context size The context position and context size are both “1”. variable bindings The union of the in-scope specified options and variables are available as variable bindings to the XPath processor. An option that has neither a specified value nor a default value will not appear as an in-scope variable. Consequently, an attempt to refer to that variable will raise an error. function library The core function library and the . in-scope namespaces The namespace bindings in-scope on the element where the expression occurred.

When a step evaluates an XPath expression using XPath 1.0, unless otherwise indicated by a particular step, it does so with the following initial context: context node The document node that appears on the primary input port of the step, unless otherwise specified by the step. context position and context size The position and size are both “1”, unless otherwise specified by the step. variable bindings None, unless otherwise specified by the step. function library The core function library, unless otherwise specified by the step. in-scope namespaces The set of namespace bindings provided by the XProc processor. The processor computes this set of bindings by taking a union of the bindings on the step element itself as well as the bindings on any of the options and parameters used in computing values for the step (see ). The results of computing the union of namespaces in the presence of conflicting declarations for a particular prefix are implementation-dependent. Some steps may also provide for implementation-defined or implementation-dependent amendments to the contexts. Those amendments are in addition to any specified by XProc.

XProc processors that support XPath 2.0 are XPath 2.0 processors. Such processors can refer to the primitive atomic schema types, but cannot import additional types. XPath 2.0 processors must implement all of the XPath 2.0 functions, but are not expect to implement the functions described in .

When the XProc processor evaluates an XPath expression using XPath 2.0, unless otherwise indicated by a particular step, it does so with the following static context: XPath 1.0 compatibility mode Is true if the indicated XPath version is 1.0, false otherwise. Statically known namespaces The namespace declarations in-scope for the containing element. Default element/type namespace The null namespace. Default function namespace The function namespace. In-scope schema definitions A basic XPath 2.0 XProc processor includes the following named type definitions in its in-scope schema definitions: All the primitive atomic types defined in , with the exception of xs:NOTATION. That is: xs:string, xs:boolean, xs:decimal, xs:double, xs:float, xs:date, xs:time, xs:dateTime, xs:duration, xs:QName, xs:anyURI, xs:gDay, xs:gMonthDay, xs:gMonth, xs:gYearMonth, xs:gYear, xs:base64Binary, and xs:hexBinary. The derived atomic type xs:integer defined in . The types xs:anyType, xs:anySimpleType, xs:yearMonthDuration, xs:dayTimeDuration, xs:anyAtomicType, xs:untyped, and xs:untypedAtomic defined in . In-scope variables The union of the in-scope specified options and variables are available as variable bindings to the XPath processor. An option that has neither a specified value nor a default value will not appear as an in-scope variable. Consequently, an attempt to refer to that variable will raise an error. Context item static type Document. Function signatures The signatures of the and the . Statically known collations Implementation-defined but must include the Unicode code point collation. The version of Unicode supported is implementation-defined, but it is recommended that the most recent version of Unicode be used. Default collation Unicode code point collation. Base URI The base URI of the element on which the expression occurs. Statically known documents None. Statically known collections None. And the following dynamic context: context item The document node of a document. The document is either specified with a binding or is taken from the default readable port. It is a dynamic error if a document sequence appears where a document to be used as the context node is expected. If there is no binding and there is no default readable port then the context node is undefined. context position and context size The context position and context size are both “1”. Variable values The union of the in-scope options and variables are available as variable bindings to the XPath processor. Function implementations The and the . Current dateTime The point in time returned as the current dateTime is implementation-defined. Implicit timezone The implicit timezone is implementation-defined. Available documents The set of available documents (those that may be retrieved with a URI) is implementation-dependent. Available collections The set of available collections is implementation-dependent. Default collection None.

When a step evaluates an XPath expression using XPath 2.0, unless otherwise indicated by a particular step, it does so with the following static context: XPath 1.0 compatibility mode Is true if the indicated XPath version is 1.0, false otherwise. Statically known namespaces The namespace declarations in-scope for the containing element or made available through p:namespaces. Default element/type namespace The null namespace. Default function namespace The function namespace. In-scope schema definitions The same as the . In-scope variables None, unless otherwise specified by the step. Context item static type Document. Function signatures The signatures of the . Statically known collations Implementation-defined but must include the Unicode code point collation. Default collation Unicode code point collation. Base URI The base URI of the element on which the expression occurs. Statically known documents None. Statically known collections None. And the following initial dynamic context: context item The document node of the document that appears on the primary input of the step, unless otherwise specified by the step. context position and context size The context position and context size are both “1”, unless otherwise specified by the step. Variable values None, unless otherwise specified by the step. Function implementations The . Current dateTime An implementation-defined point in time. Implicit timezone The implicit timezone is implementation-defined. Available documents The set of available documents (those that may be retrieved with a URI) is implementation-dependent. Available collections None. Default collection None. Some steps may also provide for implementation-defined or implementation-dependent amendments to the contexts. Those amendments are in addition to any specified by XProc.

The XProc processor must support a few additional functions in XPath expressions evaluated by the processor. In the following descriptions, the names of types (string, boolean, etc.) should be taken to mean the corresponding data types for an implementation that uses XPath 2.0 and as the most appropriate XPath 1.0 types for an XPath 1.0 implementation.

XPath expressions within a pipeline document can interrogate the processor for information about the current state of the pipeline. Various aspects of the processor are exposed through the p:system-property function in the pipeline namespace: Function: string p:system-property(string property) The property string must have the form of a QName; the QName is expanded into a name using the namespace declarations in scope for the expression. It is a dynamic error if the specified QName cannot be resolved with the in-scope namespace declarations. The p:system-property function returns the string representing the value of the system property identified by the QName. If there is no such property, the empty string must be returned. Implementations must provide the following system properties, which are all in the XProc namespace: p:episode Returns a string which should be unique for each invocation of the pipeline processor. In other words, if a processor is run several times in succession, or if several processors are running simultaneously, each invocation of each processor should get a distinct value from p:episode. The unique identifier must be a valid XML name. p:language Returns a string which identifies the current language, for example, for message localization purposes. The exact format of the language string is implementation-defined but should be consistent with the xml:lang attribute. p:product-name Returns a string containing the name of the implementation, as defined by the implementer. This should normally remain constant from one release of the product to the next. It should also be constant across platforms in cases where the same source code is used to produce compatible products for multiple execution platforms. p:product-version Returns a string identifying the version of the implementation, as defined by the implementer. This should normally vary from one release of the product to the next, and at the discretion of the implementer it may also vary across different execution platforms. p:vendor Returns a string which identifies the vendor of the processor. p:vendor-uri Returns a URI which identifies the vendor of the processor. Often, this is the URI of the vendor's web site. p:version Returns the version of XProc implemented by the processor; for processors implementing the version of XProc specified by this document, the value is “1.0”. The value of the version attribute is a token (i.e., an xs:token per ). p:xpath-version Returns the version(s) of XPath implemented by the processor for evaluating XPath expressions on XProc elements. The result is a list of versions supported. For example, a processor that only supports XPath 1.0 would return “1.0”; a processor that supports XPath 2.0 and XPath 1.0 backwards compatibility mode could return “1.0 2.0”; a processor that supports only XPath 2.0 would return “2.0”. p:psvi-supported Returns true if the implementation supports passing PSVI annotations between steps, false otherwise.

The p:step-available function reports whether or not a particular type of step is understood by the processor. Function: boolean p:step-available(string step-type) The step-type string must have the form of a QName; the QName is expanded into a name using the namespace declarations in scope for the expression. The p:step-available function returns true if and only if the processor knows how to evaluate steps of the specified type.

In the context of a p:for-each or a p:viewport, the p:iteration-position function reports the position of the document being processed in the sequence of documents that will be processed. In the context of other standard XProc compound steps, it returns 1. Function: integer p:iteration-position() In the context of an extension compound step, the value returned by p:iteration-position is implementation-defined.

In the context of a p:for-each or a p:viewport, the p:iteration-size function reports the number of documents in the sequence of documents that will be processed. In the context of other standard XProc compound steps, it returns 1. Function: integer p:iteration-size() In the context of an extension compound step, the value returned by p:iteration-size is implementation-defined.

Returns the base URI of the specified node, if it has one. This function provides an interoperable way for XPath 1.0 based processors to access the base URI of a node. It is conceptually the same as the XPath 2.0 fn:base-uri() function. Function: string p:base-uri() Function: string p:base-uri(Node node) If no argument is specified, the context node is taken to be the argument. This function returns the [base-uri] property of its argument, or the empty string if no base URI is defined for that argument or argument type. This function is defined in our namespace because it would be inappropriate to require XPath 1.0 based processors to support the fn:base-uri function; its semantics are deeply rooted in the XPath 2.0 data model which differs from the XPath 1.0 data model.

Resolves a relative URI with respect to a particular base URI. This function provides an interoperable way for XPath 1.0 based processors to compose URI references. It is conceptually the same as the XPath 2.0 fn:resolve-uri() function. Function: string p:resolve-uri(String relative) Function: string p:resolve-uri(String relative, String base) If no base is specified, the base URI of the context node is used. This function is defined in our namespace because it would be inappropriate to require XPath 1.0 based processors to support the fn:resolve-uri function; its semantics are rooted in the XPath 2.0 data model which differs from the XPath 1.0 data model.

It is implementation-defined if the processor supports any other XPath extension functions. Additional extension functions, if any, must not use any of the XProc namespaces.

XML documents flow between steps in an XProc pipeline. identifies the properties of those documents that must be available. Implementations may also have the ability to pass PSVI annotations between steps. Whether or not the pipeline processor supports passing PSVI annotations between steps is implementation-defined. The exact PSVI properties that are preserved when documents are passed between steps is implementation-defined. A pipeline can use the p:psvi-supported system property to determine whether or not PSVI properties can be passed between steps. A pipeline can assert that PSVI support is required with the psvi-required attribute: On a p:pipeline or p:declare-step, psvi-required indicates whether or not the declared step requires PSVI support. It is a dynamic error if a processor that does not support PSVI annotations attempts to invoke a step which asserts that they are required. On a p:library, the psvi-required attribute provides a default value for all of its p:pipeline and p:declare-step children that do not specify a value themselves. Many of the steps that an XProc pipeline can use are transformative in nature. The p:delete step, for example, can remove elements and attributes; the p:label-elements step can add attributes; etc. If PSVI annotations were always preserved, the use of such steps could result in documents that were inconsistent with their schema annotations. In order to avoid these inconsistencies, most steps must not produce PSVI annotated results even when PSVI passing is supported. If PSVI passing is supported, the following constraints apply: Implementations must faithfully transmit any PSVI properties produced on step outputs to the steps to which they are connected. When only a subset of the input is processed by a step (because a select expression appears on an input port or a match expression is used to process only part of the input), any PSVI annotations that appear on the selected input must be preserved in the resulting documents passed to the step. Note that ID/IDREF constraints, and any other whole-document constraints, may not be satisfied within the selected portion, irrespective of what its PSVI properties claim. If an output of a compound step is bound to an output which includes PSVI properties, those properties must be preserved on the output of the compound step, except for the output of p:viewport which must not contain any PSVI properties. If an implementation supports XPath 2.0, the data model constructed with which to evaluate XPath expressions and match patterns should take advantage of as much PSVI information as possible. Except as specified above, or in the descriptions of individual steps, implementations must not include PSVI properties in the outputs of steps defined by this specification. It is implementation-defined what PSVI properties, if any, are produced by extension steps. The exceptions in the standard XProc steps are the p:validate-with-xml-schema, p:validate-with-relax-ng, and p:validate-with-schematron steps, p:xslt (when XSLT 2.0 is used), p:xquery, p:identity, and p:split-sequence. A processor that supports passing PSVI properties between steps is always free to do so. Even if psvi-required="false" is explicitly specified, it is not an error for a step to produce a result that includes additional PSVI properties, provide it does not violate the constraints above.

Variables are name/value pairs. Pipeline authors can create variables to hold computed values. A variable is a name/value pair where the name is an expanded name and the value must be a string or xs:untypedAtomic. Variables and options share the same scope and may shadow each other.

Some steps accept options. Options are name/value pairs, like variables. Unlike variables, the value of an option can be changed by the caller. An option is a name/value pair where the name is an expanded name and the value must be a string or xs:untypedAtomic. The options declared on a step are its declared options. Option names are always expressed as literal values, pipelines cannot construct option names dynamically. The options on a step which have specified values, either because a p:with-option element specifies a value or because the declaration included a default value, are its specified options. How outside values are specified for pipeline options on the pipeline initially invoked by the processor is implementation-defined. In other words, the command line options, APIs, or other mechanisms available to specify such options values are outside the scope of this specification.

Some steps accept parameters. Parameters are name/value pairs, like variables and options. Unlike variables and options, which have names known in advance to the pipeline, parameters are not declared and their names may be unknown to the pipeline author. Pipelines can dynamically construct sets of parameters. Steps can read dynamically constructed sets on parameter input ports. A parameter is a name/value pair where the name is an expanded name and the value must be a string or xs:untypedAtomic. A parameter input port is a distinguished kind of input port which accepts (only) dynamically constructed parameter name/value pairs. See . Analogous to primary input ports, steps that have parameter inputs may designate at most one parameter input port as a primary parameter input port. If a step has a parameter input port which is explicitly marked “primary='true'”, or if it has exactly one parameter input port and that port is not explicitly marked “primary='false'”, then that parameter input port is the primary parameter input port of the step. If a step has a single parameter input port and that port is explicitly marked “primary='false'”, or if a step has more than one parameter input port and none is explicitly marked as the primary, then the primary parameter input port of that step is undefined. How outside values are specified for pipeline parameters on the pipeline initially invoked by the processor is implementation-defined. In other words, the command line options, APIs, or other mechanisms available to specify such parameter values are outside the scope of this specification.

An XProc pipeline may attempt to access arbitrary network resources: steps such as p:load and p:http-request can attempt to read from an arbitrary URI; steps such as p:store can attempt to write to an arbitrary location; p:exec can attempt to execute an arbitrary program. Note, also, that some steps, such as p:xslt and p:xquery, include extension mechanisms which may attempt to execute arbitrary code. In some environments, it may be inappropriate to provide the XProc pipeline with access to these resources. In a server environment, for example, it may be impractical to allow pipelines to store data. In environments where the pipeline cannot be trusted, allowing the pipeline to access arbitrary resources or execute arbitrary code may be a security risk. It is a dynamic error for a pipeline to attempt to access a resource for which it has insufficient privileges or perform a step which is forbidden. Steps in a pipeline may call themselves recursively which could result in pipelines which will never terminate. A conformant XProc processor may limit the resources available to any or all steps in a pipeline. A conformant implementation may raise dynamic errors, or take any other corrective action, for any security problems that it detects.

A pipeline author may identify the version of XProc against which a particular pipeline was authored by explicitly importing the library that identifies the steps defined by that version of XProc. For the version defined by this specification, the library is “http://www.w3.org/2008/xproc-1.0.xpl”. If the version is not explicitly identified, the implicit version should be the most recent version known to the processor. When a processor encounters a version it does not recognize, it proceeds in forwards-compatible mode. In forwards-compatible mode: The library that identifies the version of XProc is imported, see p:import. This provides the processor with declarations for any new step types. It is a dynamic error to attempt to evaluate a step type for which no implementation is known, but conditional processing and the step-available function can be used to write backwards-compatible pipelines. It is a static error if the signature of a known step in the version library has changed, except for new options. New options on known steps are ignored in the pipeline. As a consequence, future specifications must not change the semantics of existing step types without changing their names.

This section describes the normative XML syntax of XProc. This syntax is sufficient to represent all the aspects of a pipeline, as set out in the preceding sections. XProc is intended to work equally well with and . Unless otherwise noted, the term “XML” refers equally to both versions. Unless otherwise noted, the term Namespaces in XML refers equally to and . Support for pipeline documents written in XML 1.1 and pipeline inputs and outputs that use XML 1.1 is implementation-defined. Elements in a pipeline document represent the pipeline, the steps it contains, the connections between those steps, the steps and connections contained within them, and so on. Each step is represented by an element; a combination of elements and attributes specify how the inputs and outputs of each step are connected and how options and parameters are passed. Conceptually, we can speak of steps as objects that have inputs and outputs, that are connected together and which may contain additional steps. Syntactically, we need a mechanism for specifying these relationships. Containment is represented naturally using nesting of XML elements. If a particular element identifies a compound step then the step elements that are its immediate children form its subpipeline. The connections between steps are expressed using names and references to those names. Six kinds of things are named in XProc: Step types, Steps, Input ports (both parameter and document), Output ports, Options and variables, and Parameters

There are three namespaces associated with XProc: http://www.w3.org/ns/xproc The namespace of the XProc XML vocabulary described by this specification; by convention, the namespace prefix “p:” is used for this namespace. http://www.w3.org/ns/xproc-step The namespace used for documents that are inputs to and outputs from several standard and optional steps described in this specification. Some steps, such as p:http-request and p:store, have defined input or output vocabularies. We use this namespace for all of those documents. The conventional prefix “c:” is used for this namespace. http://www.w3.org/ns/xproc-error The namespace used for errors. The conventional prefix “err:” is used for this namespace. This specification also makes use of the prefix “xs:” to refer to the namespace http://www.w3.org/2001/XMLSchema.

Names are used to identify step types, steps, ports, options and variables, and parameters. Step types, options, variables, and parameters are named with QNames. Steps and ports are named with NCNames. The scope of a name is a measure of where it is available in a pipeline. If two names are in the same scope, we say that they are visible to each other. The scope of the names of the step types is the pipeline in which they are declared, including any declarations imported from libraries via p:import. Nested pipelines inherit the step types in scope for their parent. In other words, the step types that are in scope in a p:pipeline or p:declare-step are: The standard, built-in types (p:pipeline, p:choose, etc.). Any implementation-provided types. Any step types declared in the pipeline. The types of any p:pipelines or p:declare-steps that are imported. Any types that are in the scope of any p:library that is imported. Any step types that are in scope for the pipeline's parent p:pipeline or p:declare-step, if it has one. The type of the pipeline itself, if it has one. The step types that are in scope in a p:library are: The standard, built-in types (p:pipeline, p:choose, etc.). Any implementation-provided types. Any step types declared in the library (the p:pipeline and p:declare-step children of the p:library element). The types of an p:pipelines or p:declare-steps that are imported into the library. Any types that are in the scope of any p:library that is imported. All the step types in a pipeline must have unique names: it is a static error if any step type name is built-in and/or declared or defined more than once in the same scope. The scope of the names of the steps themselves is determined by the environment of each step. In general, the name of a step, the names of its sibling steps, the names of any steps that it contains directly, the names of its ancestors, and the names of the siblings of its ancestors are all in a common scope. All steps in the same scope must have unique names: it is a static error if two steps with the same name appear in the same scope. The scope of an input or output port name is the step on which it is defined. The names of all the ports on any step must be unique. Taken together, these uniqueness constraints guarantee that the combination of a step name and a port name uniquely identifies exactly one port on exactly one in-scope step. The scope of option and variable names is determined by where they are declared. When an option is declared with p:option (or a variable with p:variable), unless otherwise specified, its scope consists of the sibling elements that follow its declaration and the descendants of those siblings. Parameter names are not scoped; they are distinct on each step.

When a relative URI appears in an option value, the base URI against which it must be made absolute is the base URI of the p:option element. If an option value is specified using a syntactic shortcut, the base URI of the step on which the shortcut attribute appears must be used. In general, whenever a relative URI appears, its base URI is the base URI of the nearest ancestor element. The pipeline author can control the base URIs of elements within the pipeline document with the xml:base attribute. The xml:base attribute may appear on any element in a pipeline and has the semantics outlined in .

A pipeline author can provide a globally unique identifier for any element in a pipeline with the xml:id attribute. The xml:id attribute may appear on any element in a pipeline and has the semantics outlined in .

A binding associates an input or output port with some data source. A document or a sequence of documents can be bound to a port in four ways: by source, by URI, by providing an inline document, or by making it explicitly empty. Each of these mechanisms is allowed on the p:input, p:output, p:xpath-context, p:iteration-source, and p:viewport-source elements. Specified by URI A document is specified by URI if it is referenced with a URI. The href attribute on the p:document or p:data element is used to refer to documents by URI. In this example, the input to the p:identity step named “otherstep” comes from “http://example.com/input.xml”. <p:output port="result"/> <p:identity name="otherstep"> <p:input port="source"> <p:document href="http://example.com/input.xml"/> </p:input> </p:identity> It is a dynamic error if the processor attempts to retrieve the URI specified on a p:document or p:data and fails. (For example, if the resource does not exist or is not accessible with the user's authentication credentials.) Specified by source A document is specified by source if it references a specific port on another step. The step and port attributes on the p:pipe element are used for this purpose. In this example, the “source” input to the p:xinclude step named “expand” comes from the “result” port of the step named “otherstep”. <p:xinclude name="expand"> <p:input port="source"> <p:pipe step="otherstep" port="result"/> </p:input> </p:xinclude> See the description of p:pipe for a complete description of the ports that can be connected. Specified inline An inline document is specified directly in the body of the element that binds it. The content of the p:inline element is used for this purpose. In this example, the “stylesheet” input to the XSLT step named “xform” comes from the content of the p:input element itself. <p:xslt name="xform"> <p:input port="stylesheet"> <p:inline> <xsl:stylesheet version="1.0"> ... </xsl:stylesheet> </p:inline> </p:input> </p:xslt> Inline documents are considered “quoted”. The pipeline processor passes them literally to the port, even if they contain elements from the XProc namespace or other namespaces that would have other semantics outside of the p:inline. Specified explicitly empty An empty sequence of documents is specified with the p:empty element. In this example, the “source” input to the XSLT 2.0 step named “generate” is explicitly empty: <p:xslt name="generate" version="2.0"> <p:input port="source"> <p:empty/> </p:input> <p:input port="stylesheet"> <p:inline> <xsl:stylesheet version="2.0"> ... </xsl:stylesheet> </p:inline> </p:input> <p:with-option name="template-name" select="'someName'"/> </p:xslt> If you omit the binding on a primary input port, a binding to the default readable port will be assumed. Making the binding explicitly empty guarantees that the binding will be to an empty sequence of documents. It is inconsistent with the specification to specify an empty binding as the context for evaluating an XPath expression. When an empty binding is specified for an XPath 1.0 expression, an empty document node must be used instead as the context node. Note that a p:input or p:output element may contain more than one p:pipe, p:document, p:data, or p:inline element. If more than one binding is provided, then the specified sequence of documents is made available on that port in the same order as the bindings.

Pipeline authors may add documentation to their pipeline documents with the p:documentation element. Except when it appears as a descendant of p:inline, the p:documentation element is completely ignored by pipeline processors, it exists simply for documentation purposes. If a p:documentation is provided as a descendant of p:inline, it has no special semantics, it is treated literally as part of the document to be provided on that port. The p:documentation element has no special semantics when it appears in documents that flow through the pipeline. Pipeline processors that inspect the contents of p:documentation elements and behave differently on the basis of what they find are not conformant. Processor extensions must be specified with p:pipeinfo.

Pipeline authors may add annotations to their pipeline documents with the p:pipeinfo element. The semantics of p:pipeinfo elements are implementation-defined. Processors should specify a way for their annotations to be identified, perhaps with extension attributes. Where p:documentation is intended for human consumption, p:pipeinfo elements are intended for processor consumption. A processor might, for example, use annotations to identify some particular aspect of an implementation, to request additional, perhaps non-standard features, to describe parallelism constraints, etc. When a p:pipeinfo appears as a descendant of p:inline, it has no special semantics; in that context it must be treated literally as part of the document to be provided on that port. The p:pipeinfo element has no special semantics when it appears in documents that flow through the pipeline.

An element from the XProc namespace may have any attribute not from the XProc namespace, provided that the expanded-QName of the attribute has a non-null namespace URI. Such an attribute is called an extension attribute. The presence of an extension attribute must not cause the connections between steps to differ from the connections that would arise in the absence of the attribute. They must not cause the processor to fail to signal an error that would be signaled in the absence of the attribute. A processor which encounters an extension attribute that it does not implement must behave as if the attribute was not present.

The description of each element in the pipeline namespace is accompanied by a syntactic summary that provides a quick overview of the element's syntax: For clarity of exposition, some attributes and elements are elided from the summaries: An xml:id attribute is allowed on any element. It has the semantics of . An xml:base attribute is allowed on any element. It has the semantics of . The p:documentation and p:pipeinfo elements are not shown, but they are allowed anywhere. The p:log element is allowed on any step that has a p:output. Attributes that are syntactic shortcuts for option values are not shown. The types given for attributes should be understood as follows: ID, NCName, NMTOKEN, NMTOKENS, anyURI, boolean, integer, string: As per including whitespace normalization as appropriate. QName: With whitespace normalization as per and according to the following definition: In the context of XProc, a QName is almost always a QName in the Namespaces in XML sense. Note, however, that p:option and p:with-param values can get their namespace declarations in a non-standard way (with p:namespaces) and QNames that have no prefix are always in no-namespace, irrespective of the default namespace. PrefixList: As a list with item type NMTOKEN, per , including whitespace normalization. XPathExpression, XSLTMatchPattern: As a string per , including whitespace normalization, and the further requirement to be a conformant Expression per or , as appropriate, or Match pattern per or , as appropriate. A number of errors apply generally: It is a static error if any element in the XProc namespace has attributes not defined by this specification unless they are extension attributes. It is a static error if any required attribute is not provided. It is a dynamic error if any attribute value does not satisfy the type required for that attribute. It is a static error if any element in the XProc namespace or any step has element children other than those specified for it by this specification. In particular, the presence of atomic steps for which there is no visible declaration may raise this error. It is a static error if any step directly contains text nodes that do not consist entirely of whitespace. It is a dynamic error if any option value does not satisfy the type required for that option. It is a static error if a compound step has no contained steps. It is a dynamic error if any attempt is made to dereference a URI where the scheme of the URI reference is not supported. Implementations are encouraged to support as many schemes as is practical and, in particular, they should support both the file: and http(s): schemes. The set of URI schemes actually supported is implementation-defined. If an XProc processor can determine statically that a dynamic error will always occur, it may report that error statically provided that the error does not occur among the descendants of a p:try. Dynamic errors inside a p:try must not be reported statically. They must be raised dynamically so that p:catch processing can be performed on them.

This section describes the core steps of XProc.

A p:pipeline declares a pipeline that can be evaluated by an XProc processor. It encapsulates the behavior of a subpipeline. Its children declare inputs, outputs, and options that the pipeline exposes and identify the steps in its subpipeline. (A p:pipeline is a simplified form of step declaration.) All p:pipeline pipelines have an implicit primary input port named “source” and an implicit primary output port named “result”. Any input or output ports that the p:pipeline declares explicitly are in addition to those ports and may not be declared primary. Viewed from the outside, a p:pipeline is a black box which performs some calculation on its inputs and produces its outputs. From the pipeline author's perspective, the computation performed by the pipeline is described in terms of contained steps which read the pipeline's inputs and produce the pipeline's outputs. If a pipeline does not have a type then that pipeline cannot be invoked as a step. The p:pipeline element is just a simplified form of step declaration. A document that reads: <p:pipeline some-attributes> some-content </p:pipeline> can be interpreted as if it read: <p:declare-step some-attributes> <p:input port='source' primary='true'/> <p:input port='parameters' kind='parameters' primary='true'/> <p:output port='result' primary='true'> some-content </p:declare-step> See p:declare-step for more details.

A pipeline might accept a document as input; perform XInclude, validation, and transformation; and produce the transformed document as its output. <p:pipeline xmlns:p="http://www.w3.org/ns/xproc"> <p:xinclude/> <p:validate-with-xml-schema> <p:input port="schema"> <p:document href="http://example.com/path/to/schema.xsd"/> </p:input> </p:validate-with-xml-schema> <p:xslt> <p:input port="stylesheet"> <p:document href="http://example.com/path/to/stylesheet.xsl"/> </p:input> </p:xslt> </p:pipeline>

A for-each is specified by the p:for-each element. It is a compound step that processes a sequence of documents, applying its subpipeline to each document in turn. When a pipeline needs to process a sequence of documents using a subpipeline that only processes a single document, the p:for-each construct can be used as a wrapper around that subpipeline. The p:for-each will apply that subpipeline to each document in the sequence in turn. The result of the p:for-each is a sequence of documents produced by processing each individual document in the input sequence. If the p:for-each has one or more output ports, what appears on each of those ports is the sequence of documents that is the concatenation of the sequence produced by each iteration of the loop on the port to which it is connected. If the iteration source for a p:for-each is an empty sequence, then the subpipeline is never run and an empty sequence is produced on all of the outputs. The p:iteration-source is an anonymous input: its binding provides a sequence of documents to the p:for-each step. If no iteration sequence is explicitly provided, then the iteration source is read from the default readable port. The processor provides each document, one at a time, to the subpipeline represented by the children of the p:for-each on a port named current. For each declared output, the processor collects all the documents that are produced for that output from all the iterations, in order, into a sequence. The result of the p:for-each on that output is that sequence of documents. The environment inherited by the contained steps of a p:for-each is the inherited environment with these modifications: The port named “current” on the p:for-each is added to the readable ports. The port named “current” on the p:for-each is made the default readable port. If the p:for-each has a primary output port (explicit or supplied by default) and that port has no binding, then it is bound to the primary output port of the last step in the subpipeline. It is a static error if the primary output port has no binding and the last step in the subpipeline does not have a primary output port. Note that outputs declared for a p:for-each serve a dual role. Inside the p:for-each, they are used to read results from the subpipeline. Outside the p:for-each, they provide the aggregated results. The sequence attribute on a p:output inside a p:for-each only applies inside the step. From the outside, all of the outputs produce sequences.

Within a p:for-each, the p:iteration-position and p:iteration-size are taken from the sequence of documents that will be processed by the p:for-each. The total number of documents is the p:iteration-size; the ordinal value of the current document (the document appearing on the current port) is the p:iteration-position. In the case where no XPath expression that must be evaluated by the processor makes any reference to p:iteration-size, its value does not actually have to be calculated (and the entire input sequence does not, therefore, need to be buffered so that its size can be calculated before processing begins).

A p:for-each might accept a sequence of chapters as its input, process each chapter in turn with XSLT, a step that accepts only a single input document, and produce a sequence of formatted chapters as its output. <p:for-each name="chapters"> <p:iteration-source select="//chapter"/> <p:output port="html-results"> <p:pipe step="make-html" port="result"/> </p:output> <p:output port="fo-results"> <p:pipe step="make-fo" port="result"/> </p:output> <p:xslt name="make-html"> <p:input port="stylesheet"> <p:document href="http://example.com/xsl/html.xsl"/> </p:input> </p:xslt> <p:xslt name="make-fo"> <p:input port="source"> <p:pipe step="chapters" port="current"/> </p:input> <p:input port="stylesheet"> <p:document href="http://example.com/xsl/fo.xsl"/> </p:input> </p:xslt> </p:for-each> The //chapter elements of the document are selected. Each chapter is transformed into HTML and XSL Formatting Objects using an XSLT step. The resulting HTML and FO documents are aggregated together and appear on the html-results and fo-results ports, respectively, of the chapters step itself.

A viewport is specified by the p:viewport element. It is a compound step that processes a single document, applying its subpipeline to one or more subtrees of the document. The result of the p:viewport is a copy of the original document where the selected subtrees have been replaced by the results of applying the subpipeline to them. The p:viewport-source is an anonymous input: its binding provides a single document to the p:viewport step. If no document is explicitly provided, then the viewport source is read from the default readable port. It is a dynamic error if the viewport source does not provide exactly one document. The match attribute specifies an XSLT match pattern. Each matching node in the source document is wrapped in a document node, as necessary, and provided, one at a time, to the viewport's subpipeline on a port named current. The base URI of the resulting document that is passed to the subpipeline is the base URI of the matched element or document. It is a dynamic error if the match expression on p:viewport does not match an element or document. After a match is found, the entire subtree rooted at that match is processed as a unit. No further attempts are made to match nodes among the descendants of any matched node. The environment inherited by the contained steps of a p:viewport is the inherited environment with these modifications: The port named “current” on the p:viewport is added to the readable ports. The port named “current” on the p:viewport is made the default readable port. The p:viewport must contain a single, primary output port explicit declared explicitly or supplied by default. If that port has no binding, then it is bound to the primary output port of the last step in the subpipeline. It is a static error if the primary output port has no binding and the last step in the subpipeline does not have a primary output port. What appears on the output from the p:viewport will be a copy of the input document where each matching node is replaced by the result of applying the subpipeline to the subtree rooted at that node. In other words, if the match pattern matches a particular element then that element is wrapped in a document node and provided on the current port, the subpipeline in the p:viewport is evaluated, and the result that appears on the output port replaces the matched element. If no documents appear on the output port, the matched element will effectively be deleted. If exactly one document appears, the contents of that document will replace the matched element. If a sequence of documents appears, then the contents of each document in that sequence (in the order it appears in the sequence) will replace the matched element. The output of the p:viewport itself is a single document that appears on a port named “result”. Note that the semantics of p:viewport are special. The output port in the p:viewport is used only to access the results of the subpipeline. The output of the step itself appears on a port with the fixed name “result” that is never explicitly declared.

Within a p:viewport, the p:iteration-position and p:iteration-size are taken from the sequence of documents that will be processed by the p:viewport. The total number of documents is the p:iteration-size; the ordinal value of the current document (the document appearing on the current port) is the p:iteration-position. In the case where no XPath expression that must be evaluated by the processor makes any reference to p:iteration-size, its value does not actually have to be calculated (and the entire input sequence does not, therefore, need to be buffered so that its size can be calculated before processing begins).

A p:viewport might accept an XHTML document as its input, add an hr element at the beginning of all div elements that have the class value “chapter”, and return an XHTML document that is the same as the original except for that change. <p:viewport match="h:div[@class='chapter']" xmlns:h="http://www.w3.org/1999/xhtml"> <p:insert position="first-child"> <p:input port="insertion"> <p:inline> <hr xmlns="http://www.w3.org/1999/xhtml"/> </p:inline> </p:input> </p:insert> </p:viewport> The nodes which match h:div[@class='chapter'] in the input document are selected. An hr is inserted as the first child of each h:div and the resulting version replaces the original h:div. The result of the whole step is a copy of the input document with a horizontal rule as the first child of each selected h:div.

A choose is specified by the p:choose element. It is a multi-container step that selects exactly one of a list of alternative subpipelines based on the evaluation of XPath expressions. A p:choose has no inputs. It contains an arbitrary number of alternative subpipelines, exactly one of which will be evaluated. The list of alternative subpipelines consists of zero or more subpipelines guarded by an XPath expression, followed optionally by a single default subpipeline. The p:choose considers each subpipeline in turn and selects the first (and only the first) subpipeline for which the guard expression evaluates to true in its context. If there are no subpipelines for which the expression evaluates to true, the default subpipeline, if it was specified, is selected. After a subpipeline is selected, it is evaluated as if only it had been present. The outputs of the p:choose are taken from the outputs of the selected subpipeline. The p:choose has the same number of outputs as the selected subpipeline with the same names. If the selected subpipeline has a primary output port, the port with the same name on the p:choose is also a primary output port. In order to ensure that the output of the p:choose is consistent irrespective of the subpipeline chosen, each subpipeline must declare the same number of outputs with the same names and the same settings with respect to sequences. If any of the subpipelines specifies a primary output port, each subpipeline must specify exactly the same output as primary. It is a static error if two subpipelines in a p:choose declare different outputs. It is a dynamic error if no subpipeline is selected by the p:choose and no default is provided. The p:choose can specify the context node against which the XPath expressions that occur on each branch are evaluated. The context node is specified as a binding for the p:xpath-context. If no binding is provided, the default p:xpath-context is the document on the default readable port. Each conditional subpipeline is represented by a p:when element. The default branch is represented by a p:otherwise element.

A p:xpath-context element specifies the context against which an XPath expression will be evaluated. When it appears in a p:when, it specifies the context for that p:when’s test attribute. When it appears in p:choose, it specifies the default context for all of the p:when elements in that p:choose. Only one binding is allowed and it works the same way that bindings work on a p:input. No select expression is allowed. It is a dynamic error if the xpath-context is bound to a sequence of documents. In an XPath 1.0 implementation, if the context node is bound to p:empty, or is unbound and the default readable port is undefined, an empty document node is used instead as the context. In an XPath 2.0 implementation, the context item is undefined.

A when specifies one subpipeline guarded by a test expression. Each p:when branch of the p:choose has a test attribute which must contain an XPath expression. That XPath expression's effective boolean value is the guard for the subpipeline contained within that p:when. The p:when can specify a context node against which its test expression is to be evaluated. That context node is specified as a binding for the p:xpath-context. If no context is specified on the p:when, the context of the p:choose is used.

An otherwise specifies the default branch; the subpipeline selected if no test expression on any preceding p:when evaluates to true.

A p:choose might test the version attribute of the document element and validate with an appropriate schema. <p:choose name="version"> <p:when test="/*[@version = 2]"> <p:validate-with-xml-schema> <p:input port="schema"> <p:document href="v2schema.xsd"/> </p:input> </p:validate-with-xml-schema> </p:when> <p:when test="/*[@version = 1]"> <p:validate-with-xml-schema> <p:input port="schema"> <p:document href="v1schema.xsd"/> </p:input> </p:validate-with-xml-schema> </p:when> <p:when test="/*[@version]"> <p:identity/> </p:when> <p:otherwise> <p:output port="result"> <!-- this output is necessary so that all the branches have the same outputs; it'll never really matter because we're just about to raise an error. --> <p:inline> <nop/> </p:inline> </p:output> <p:error code="NOVERSION"> <p:input port="source"> <p:inline> <message>Required version attribute missing.</message> </p:inline> </p:input> </p:error> </p:otherwise> </p:choose>

A group is specified by the p:group element. In a p:try, it is a non-step wrapper, everywhere else, it is a compound step. A group encapsulates the behavior of its subpipeline. A p:group is a convenience wrapper for a collection of steps.

<p:group> <p:variable name="db-key" select="'some-long-string-of-nearly-random-characters'"/> <p:choose> <p:when test="/config/output = 'fo'"> <p:xslt> <p:with-param name="key" select="$db-key"/> <p:input port="stylesheet"> <p:document href="fo.xsl"/> </p:input> </p:xslt> </p:when> <p:when test="/config/output = 'svg'"> <p:xslt> <p:with-param name="key" select="$db-key"/> <p:input port="stylesheet"> <p:document href="svg.xsl"/> </p:input> </p:xslt> </p:when> <p:otherwise> <p:xslt> <p:with-param name="key" select="$db-key"/> <p:input port="stylesheet"> <p:document href="html.xsl"/> </p:input> </p:xslt> </p:otherwise> </p:choose> </p:group>

A try/catch is specified by the p:try element. It is a multi-container step that isolates a subpipeline, preventing any dynamic errors that arise within it from being exposed to the rest of the pipeline. The p:group represents the initial subpipeline and the recovery (or “catch”) pipeline is identified with a p:catch element. The p:try step evaluates the initial subpipeline and, if no errors occur, the outputs of that pipeline are the outputs of the p:try step. However, if any errors occur, the p:try abandons the first subpipeline, discarding any output that it might have generated, and evaluates the recovery subpipeline. If the recovery subpipeline is evaluated, the outputs of the recovery subpipeline are the outputs of the p:try step. If the recovery subpipeline is evaluated and a step within that subpipeline fails, the p:try fails. The outputs of the p:try are taken from the outputs of the initial subpipeline or the recovery subpipeline if an error occurred in the initial subpipeline. The p:try has the same number of outputs as the selected subpipeline with the same names. If the selected subpipeline has a primary output port, the port with the same name on the p:try is also a primary output port. In order to ensure that the output of the p:try is consistent irrespective of whether the initial subpipeline provides its output or the recovery subpipeline does, both subpipelines must declare the same number of outputs with the same names and the same settings with respect to sequences. If either of the subpipelines specifies a primary output port, both subpipelines must specify exactly the same output as primary. It is a static error if the p:group and p:catch subpipelines declare different outputs. A pipeline author can cause an error to occur with the p:error step. The recovery subpipeline of a p:try is identified with a p:catch: The environment inherited by the contained steps of the p:catch is the inherited environment with this modification: The port named “error” on the p:catch is added to the readable ports. What appears on the error output port is an error document. The error document may contain messages generated by steps that were part of the initial subpipeline. Not all messages that appear are indicative of errors; for example, it is common for all xsl:message output from the XSLT component to appear on the error output port. It is possible that the component which fails may not produce any messages at all. It is also possible that the failure of one component may cause others to fail so that there may be multiple failure messages in the document.

In general, it is very difficult to predict error behavior. Step failure may be catastrophic (programmer error), or it may be be the result of user error, resource failures, etc. Steps may detect more than one error, and the failure of one step may cause other steps to fail as well. The p:try/p:catch mechanism gives pipeline authors the opportunity to process the errors that caused the p:try to fail. In order to facilitate some modicum of interoperability among processors, errors that are reported on the error output port of a p:catch should conform to the format described here.

The error vocabulary consists of a root element, c:errors which contains zero or more c:error elements.

Each specific error is represented by an c:error element: The name and type attributes identify the name and type, respectively, of the step which failed. The code is a QName which identifies the error. For steps which have defined error codes, this is an opportunity for the step to identify the error in a machine-processable fashion. Many steps omit this because they do not include the concept of errors identified by QNames. If the error was caused by a specific document, or by the location of some erroneous construction in a specific document, the href, line, column, and offset attributes identify this location. Generally, the error location is identified either with line and column numbers or with an offset from the beginning of the document, but not usually both. The content of the c:error element is any well-formed XML. Specific steps, or specific implementations, may provide more detail about the format of the content of an error message.

Consider the following XSLT stylesheet: This stylesheet is pointless . ]]> If it was used in a step named “xform” in a p:try, the following error document might be produced: This stylesheet is pointless. ]]> It is not an error for steps to generate non-standard error output as long as it is well-formed.

A pipeline might attempt to process a document by dispatching it to some web service. If the web service succeeds, then those results are passed to the rest of the pipeline. However, if the web service cannot be contacted or reports an error, the p:catch step can provide some sort of default for the rest of the pipeline. <p:try> <p:group> <p:http-request> <p:input port="source"> <p:inline> <c:request method="post" href="http://example.com/form-action"> <c:entity-body content-type="application/x-www-form-urlencoded"> <c:body>name=W3C&amp;spec=XProc</c:body> </c:entity-body> </c:request> </p:inline> </p:input> </p:http-request> </p:group> <p:catch> <p:identity> <p:input port="source"> <p:inline> <c:error>HTTP Request Failed</c:error> </p:inline> </p:input> </p:identity> </p:catch> </p:try>

In addition to the six step types described in the preceding sections, XProc provides a standard library of atomic step types. The full vocabulary of standards steps is described in . All of the standard, atomic steps are invoked in the same way: Where “p:atomic-step” must be in the XProc namespace and must be declared in either the standard library for the XProc version supported by the processor or explicitly imported by the surrounding pipeline (see ).

Pipeline authors may also have access to additional steps not defined or described by this specification. Atomic extension steps are invoked just like standard steps: Extension steps must not be in the XProc namespace and there must be a visible step declaration at the point of use (see ). If the relevant step declaration has no subpipeline, then that step invokes the declared atomic step, which the processor must know how to perform. These steps are implementation-defined extensions. If the relevant step declaration has a subpipeline, then that step runs the declared subpipeline. These steps are user- or implementation-defined extensions. Pipelines can refer to themselves (recursion is allowed), to pipelines defined in imported libraries, and to other pipelines in the same library if they are in a library. It is a static error if a pipeline contains a step whose specified inputs, outputs, and options do not match the signature for steps of that type. It is a dynamic error if the running pipeline attempts to invoke a step which the processor does not know how to perform. The presence of other compound steps is implementation-defined; XProc provides no standard mechanism for defining them or describing what they can contain. It is a static error to use a declared step as a compound step.

Namespace qualified attributes on a step are extension attributes. Attributes, other than name, that are not namespace qualified are treated as a syntactic shortcut for specifying the value of an option. In other words, the following two steps are equivalent: The first step uses the standard p:with-option syntax: ]]> The second step uses the syntactic shortcut: ]]> Note that there are significant limitations to this shortcut syntax: It only applies to option names that are not in a namespace. It only applies to option names that are not otherwise used on the step, such as “name”. It can only be used to specify a constant value. Options that are computed at runtime must be written using the longer form. It is a static error if an option is specified with both the shortcut form and the long form. It is a static error to use an option on an atomic step that is not declared on steps of that type. The syntactic shortcuts apply equally to standard atomic steps and extension atomic steps.

A p:input identifies an input port for a step. In some contexts, p:input declares that a port with the specified name exists and identifies the properties of that port. In other contexts, it provides a binding for a port declared elsewhere. And in some contexts, it does both. The semantics of p:input are complicated further by the fact that there are two kinds of inputs, ordinary “document” inputs and “parameter” inputs.

The declaration of a document input identifies the name of the port, whether or not the port accepts a sequence, whether or not the port is a primary input port, and may provide a default binding for the port. An input declaration has the following form: The port attribute defines the name of the port. It is a static error to identify two ports with the same name on the same step. The sequence attribute determines whether or not a sequence of documents is allowed on the port. If sequence is not specified, or has the value false, then it is a dynamic error unless exactly one document appears on the declared port. The primary attribute is used to identify the primary input port. An input port is a primary input port if primary is specified with the value true or if the step has only a single input port and primary is not specified. It is a static error to specify that more than one input port is the primary. The kind attribute distinguishes between the two kinds of inputs: document inputs and parameter inputs. An input port is a document input port if kind is specified with the value “document” or if kind is not specified. If a binding is provided in the declaration, then select may be used to select a portion of the input identified by the p:empty, p:document, p:data, or p:inline elements in the p:input. The p:pipe element is explicitly excluded from a declaration because it would make the default value of an input dependent on the execution of some part of the pipeline. Default values are designed so that they can be computed statically. On a p:declare-step for an atomic step, the p:input simply declares the input port. It is a static error to attempt to provide a binding for an input port on the declaration of an atomic step. An input binding has the following form: If no binding is provided for a primary input port, the input will be bound to the default readable port. It is a static error if no binding is provided and the default readable port is undefined. A select expression may also be provided with a binding. The select expression, if specified, applies the specified XPath select expression to the document(s) that are read. Each selected node is wrapped in a document (unless it is a document) and provided to the input port. In other words, <p:input port="source"> <p:document href="http://example.org/input.html"/> </p:input> provides a single document, but <p:input port="source" select="//html:div" xmlns:html="http://www.w3.org/1999/xhtml"> <p:document href="http://example.org/input.html"/> </p:input> provides a sequence of zero or more documents, one for each html:div in http://example.org/input.html. (Note that in the case of nested html:div elements, this may result in the same content being returned in several documents.) A select expression can equally be applied to input read from another step. This input: <p:input port="source" select="//html:div" xmlns:html="http://www.w3.org/1999/xhtml"> <p:pipe step="origin" port="result"/> </p:input> provides a sequence of zero or more documents, one for each html:div in the document (or each of the documents) that is read from the result port of the step named origin. It is a dynamic error if the select expression on a p:input returns atomic values or anything other than element or document nodes. An input declaration may include a default binding. If no binding is provided for an input port which has a default binding, then the input is treated as if the default binding appeared. A default binding does not satisfy the requirement that a primary input port is automatically connected by the processor, nor is it used when no default readable port is defined. In other words, a p:declare-step or a p:pipeline can define defaults for all of its inputs, whether they are primary or not, but defining a default for a primary input usually has no effect. It's never used by an atomic step since the step, when it's called, will always bind the primary input port to the default readable port (or cause a static error). The only case where it has value is on a p:pipeline when that pipeline is invoked directly by the processor. In that case, the processor must use the default binding if no external binding is provided for the port.

The declaration of a parameter input identifies the name of the port and that the port is a parameter input. The port attribute defines the name of the port. It is a static error to identify two ports with the same name on the same step. The sequence attribute determines whether or not a sequence of documents is allowed on the port. A sequence of documents is always allowed on a parameter input port. It is a static error to specify any value other than true. The primary attribute is used to identify the primary parameter input port. An input port is a primary parameter input port if it is a parameter input port and primary is specified with the value true or if the step has only a single parameter input port and primary is not specified. It is a static error to specify that more than one parameter input port is the primary. The kind attribute distinguishes between the two kinds of inputs: document inputs and parameter inputs. An input port is a parameter input port only if the kind attribute is specified with the value “parameter”. It is a static error to specify any kind of input other than “document” or “parameter”. A parameter input port is a distinguished kind of input port. It exists only to receive computed parameters; if a step does not have a parameter input port then it cannot receive parameters. A parameter input port must satisfy all the constraints of a normal, document input port. It is a static error if the declaration of a parameter input port contains a binding; parameter input port declarations must be empty. When used on a step, parameter input ports are bound just like ordinary document ports. Parameter input ports always accept a sequence of documents. If no binding is provided for a primary parameter input port, then the port will be bound to the primary parameter input port of the pipeline which contains the step. If no binding is provided for a parameter input port other than the primary parameter input port, then the port will be bound to an empty sequence of documents. It is a static error if a primary parameter input port has no binding and the pipeline that contains the step has no primary parameter input port. If a parameter input port on a p:pipeline is not bound, it is treated as if it was bound to an automatically created p:sink step. In other words, if a p:pipeline does not contain any steps that have parameter input ports, or if those ports are all explicitly bound elsewhere, the parameter input port is ignored. In this one case, it is not an error for an input port to be unbound. If a binding is manufactured for a primary parameter input port, that binding occurs logically last among the other parameters, options, and bindings passed to the step. In other words, the parameter values that appear on that port will be used even if other values were specified with p:with-param elements. Users can change this priority by making the binding explicit and placing any p:with-param elements that they wish to function as overrides after the binding. All of the documents that appear on a parameter input must either be c:param documents or c:param-set documents. A step which accepts a parameter input reads all of the documents presented on that port, using each c:param (either at the root or inside the c:param-set) to establish the value of the named parameter. If the same name appears more than once, the last value specified is used. If the step also has literal p:with-param elements, they are are also considered in document order. In other words, p:with-param elements that appear before the parameter input may be overridden by the computed parameters; p:with-param elements that appear after may override the computed values. Consider the example in . <p:pipeline xmlns:p="http://www.w3.org/ns/xproc" name="main"> <p:xslt> <p:input port="source"> <p:pipe step="main" port="source"/> </p:input> <p:input port="stylesheet"> <p:document href="http://example.com/stylesheets/doc.xsl"/> </p:input> <p:with-param name="output-type" select="'html'"/> <p:input port="parameters"> <p:pipe step="main" port="parameters"/> </p:input> </p:xslt> </p:pipeline> This p:pipeline declares that it accepts parameters. Suppose that (through some implementation-defined mechanism) I have passed the parameters “output-type=fo” and “profile=unclassified” to the pipeline. These parameters are available on the parameters input port. When the XSLT step runs, it will read those parameters and combine them with any parameters specified literally on the step. Because the parameter input comes after the literal declaration for output-type on the step, the XSLT stylesheet will see both values that I passed in (“output-type=fo” and “profile=unclassified”). If the parameter input came before the literal declaration, then the XSLT stylesheet would see “output-type=html” and “profile=unclassified”. Most steps don't bother to declare parameter inputs, or provide explicit bindings for them, and “the right thing” usually happens.

A c:param represents a parameter on a parameter input. The name attribute of the c:param must have the lexical form of a QName. If the namespace attribute is specified, then the expanded name of the parameter is constructed from the specified namespace and the name value. It is a dynamic error if the namespace attribute is specified, the name contains a colon, and the specified namespace is not the same as the in-scope namespace binding for the specified prefix. If the namespace attribute is not specified, and the name contains a colon, then the expanded name of the parameter is constructed using the name value and the namespace declarations in-scope on the c:param element. If the namespace attribute is not specified, and the name does not contain a colon, then the expanded name of the parameter is in no namespace. Any namespace-qualified attribute names that appear on the c:param element are ignored. It is a dynamic error for any unqualified attribute names other than “name”, “namespace”, or “value” to appear on a c:param element.

A c:param-set represents a set of parameters on a parameter input. The c:param-set contains zero or more c:param elements. It is a dynamic error if the parameter list contains any elements other than c:param. Any namespace-qualified attribute names that appear on the c:param-set element are ignored. It is a dynamic error for any unqualified attribute names to appear on a c:param-set element.

A p:iteration-source identifies input to a p:for-each. The select attribute and binding of a p:iteration-source work the same way that they do in a p:input.

A p:viewport-source identifies input to a p:viewport. Only one binding is allowed and it works the same way that bindings work on a p:input. It is a dynamic error unless exactly one document appears on the p:viewport-source. No select expression is allowed.

A p:output identifies an output port, optionally binding an input for it, if necessary. The port attribute defines the name of the port. It is a static error to identify two ports with the same name on the same step. An output declaration can indicate if a sequence of documents is allowed to appear on the declared port. If sequence is specified with the value true, then a sequence is allowed. If sequence is not specified on p:output, or has the value false, then it is a dynamic error if the step does not produce exactly one document on the declared port. The primary attribute is used to identify the primary output port. An output port is a primary output port if primary is specified with the value true or if the step has only a single output port and primary is not specified. It is a static error to identify more than one output port as primary. On compound steps, the declaration may be accompanied by a binding for the output. It is a static error to specify a binding for a p:output inside a p:declare-step for an atomic step. If a binding is provided for a p:output, documents are read from that binding and those documents form the output that is written to the output port. In other words, placing a p:document inside a p:output causes the processor to read that document and provide it on the output port. It does not cause the processor to write the output to that document.

A p:log element is a debugging aid. It associates a URI with a specific output port on a step: The semantics of p:log are that it writes to the specified URI whatever document or documents appear on the specified port. If the href attribute is not specified, the location of the log file or files is implementation-defined. How a sequence of documents is represented in a p:log is implementation-defined. It is a static error if the port specified on the p:log is not the name of an output port on the step in which it appears or if more than one p:log element is applied to the same port. Implementations may, at user option, ignore all p:log elements. This element represents a potential security risk: running unexamined 3rd-party pipelines could result in vital system resources being overwritten.

The p:serialization element allows the user to request serialization properties on a p:pipeline output. If the pipeline processor serializes the output on the specified port, it must use the serialization options specified. If the processor is not serializing (if, for example, the pipeline has been called from another pipeline), then the p:serialization must be ignored. The processor may reject statically a pipeline that requests serialization options that it cannot provide. The default value of any serialization options not specified on a particular p:serialization element is implementation-defined. It is a dynamic error if the combination of serialization options specified or defaulted is not allowed. The allowed options are defined by . The semantics of the attributes on a p:serialization are described in . It is a static error if the port specified on the p:serialization is not the name of an output port on the pipeline in which it appears or if more than one p:serialization element is applied to the same port.

Variables, options, and parameters provide a mechanism for pipeline authors to construct temporary results and hold onto them for reuse. Variables are created in compound steps and, like XSLT variables, are single assignment, though they may be shadowed by subsequent declarations of other variables with the same name. Options can be declared on atomic or compound steps. The value of an option can be specified by the caller invoking the step. Any value specified by the caller takes precedence over any default value specified in the declaration. Parameters, unlike options and variables, have names that can be computed at runtime. The most common use of parameters is to pass parameter values to XSLT stylesheets.

A p:variable declares a variable and associates a value with it. The name of the variable must be a QName. If it does not contain a prefix then it is in no namespace. It is a static error to declare an option or variable in the XProc namespace. The variable's value is specified with a select attribute. It is a static error if the select attribute is not specified. The content of the select attribute is an XPath expression which will be evaluated to provide the value of the variable. If a select expression is given, it is evaluated as an XPath expression using the appropriate context as described in , for the enclosing container, with the addition of bindings for all preceding-sibling p:variable and p:option elements. Regardless of the implicit type of the expression, when XPath 1.0 is being used, the string value of the expression becomes the value of the variable; when XPath 2.0 is being used, the type is treated as an xs:untypedAtomic. Since all in-scope bindings are present in the Processor XPath Context as variable bindings, select expressions may refer to the value of in-scope bindings by variable reference. If a variable reference uses a QName that is not the name of an in-scope binding, an XPath evaluation error will occur. If a select expression is given, the readable ports available for document binding are the readable ports in the environment inherited by the first step in the surrounding container's contained steps. However, in order to avoid ordering paradoxes, it is a static error for a variable's document binding to refer to the output port of any step in the surrounding container's contained steps. If a select expression is given but no document binding is provided, the implicit binding is to the default readable port in the environment inherited by the first step in the surrounding container's contained steps. It is a static error if no document binding is provided and the default readable port is undefined. It is a dynamic error if a document sequence is specified in the document binding for a p:variable. In an XPath 1.0 implementation, if p:empty is given as the document binding, an empty document node is used as the context node. In an XPath 2.0 implementation, the context item is undefined.

A p:option declares an option and may associate a default value with it. The p:option tag can only be used in a p:declare-step or a p:pipeline (which is a syntactic abbreviation for a step declaration). The name of the option must be a QName. If it does not contain a prefix then it is in no namespace. It is a static error to declare an option or variable in the XProc namespace. It is a static error to declare two or more options on the same step with the same name. An option may be declared as required. If an option is required, it is a static error to invoke the step without specifying a value for that option. If an option is not declared to be required, it may be given a default value. The value is specified with a select attribute. It is a static error to specify that an option is both required and has a default value. If a select attribute is specified, its content is an XPath expression which will be evaluated to provide the value of the variable, which may differ from one instance of the step type to another. The select expression is only evaluated when its actual value is needed by an instance of the step type being declared. In this case, it is evaluated as described in except that In an XPath 1.0 implementation, an empty document node is used as the context. In an XPath 2.0 implementation, the context item is undefined. the variable bindings consist only of bindings for options whose declaration precedes the p:option itself in the surrounding step signature; the in-scope namespaces are the in-scope namespaces of the p:option itself. It is a dynamic error if the select expression refers to the context or to a QName that is not the name of a preceding sibling p:option. Regardless of the implicit type of the expression, when XPath 1.0 is being used, the string value of the expression becomes the value of the option; when XPath 2.0 is being used, the value is an xs:untypedAtomic.

A p:with-option provides an actual value for an option when a step is invoked. The name of the option must be a QName. If it does not contain a prefix then it is in no namespace. It is a static error to use an option name in p:with-option if the step type being invoked has not declared an option with that name. It is a static error to include more than one p:with-option with the same option name as part of the same step invocation. The actual value is specified with a select attribute. It is a static error if the select attribute is not specified. The value of the select attribute is an XPath expression which will be evaluated to provide the value of the variable. Regardless of the implicit type of the expression, when XPath 1.0 is being used, the string value of the expression becomes the value of the option; when XPath 2.0 is being used, the value is an xs:untypedAtomic. All in-scope bindings for the step instance itself are present in the Processor XPath Context as variable bindings, so select expressions may refer to any option or variable bound in those in-scope bindings by variable reference. If a variable reference uses a QName that is not the name of an in-scope binding or preceding sibling option, an XPath evaluation error will occur. If a select expression is used but no document binding is provided, the implicit binding is to the default readable port. It is a static error if no document binding is provided and the default readable port is undefined. It is a dynamic error if a document sequence is specified in the binding for a p:with-option. In an XPath 1.0 implementation, if p:empty is given as the document binding, an empty document node is used as the context node. In an XPath 2.0 implementation, the context item is undefined.

The p:with-param element is used to establish the value of a parameter. The parameter must be given a value when it is used. (Parameter names aren't known in advance; there's no provision for declaring them.) The name of the parameter must be a QName. If it does not contain a prefix then it is in no namespace. It is a static error to use the XProc namespace in the name of a parameter. The value is specified with a select attribute. It is a static error if the select attribute is not specified. The content of the select attribute is an XPath expression which will be evaluated to provide the value of the variable. The values of parameters for a step must be computed after all the options in the step's signature have had their values computed. If a select expression is given on a p:with-param, it is evaluated as an XPath expression using the appropriate context as described in , for the containing step, with the addition of variable bindings for all options declared in the containing step's signature. Regardless of the implicit type of the expression, when XPath 1.0 is being used, the string value of the expression becomes the value of the parameter; when XPath 2.0 is being used, the value is an xs:untypedAtomic. All in-scope bindings for the step instance itself are present in the Processor XPath Context as variable bindings, so select expressions may refer to any option or variable bound in those in-scope bindings, as well as to any option declared in the step signature, by variable reference. If a variable reference uses a QName that is not the name of an in-scope binding or declared option, an XPath evaluation error will occur. If a select expression is used but no document binding is provided, the implicit binding is to the default readable port. It is a static error if no document binding is provided and the default readable port is undefined. It is a dynamic error if a document sequence is specified in the binding for a p:with-param. In an XPath 1.0 implementation, if p:empty is given as the document binding, an empty document node is used as the context node. In an XPath 2.0 implementation, the context item is undefined. If the optional port attribute is specified, then the parameter appears on the named port, otherwise the parameter appears on the step's primary parameter input port. It is a static error if the specified port is not a parameter input port or if no port is specified and the step does not have a primary parameter input port.

Variable, option and parameter values carry with them not only their literal or computed string value but also a set of namespaces. To see why this is necessary, consider the following step: <p:delete xmlns:p="http://www.w3.org/ns/xproc"> <p:with-option name="match" select="'html:div'" xmlns:html="http://www.w3.org/1999/xhtml"/> </p:delete> The p:delete step will delete elements that match the expression “html:div”, but that expression can only be correctly interpreted if there's a namespace binding for the prefix “html” so that binding has to travel with the option. The default namespace bindings associated with a variable, option or parameter value are computed as follows: If the select attribute was used to specify the value and it consisted of a single VariableReference (per or , as appropriate), then the namespace bindings from the referenced option or variable are used. If the select attribute was used to specify the value and it evaluated to a node-set, then the in-scope namespaces from the first node in the selected node-set (or, if it's not an element, its parent) are used. The expression is evaluated in the appropriate context, See . Otherwise, the in-scope namespaces from the element providing the value are used. (For options specified using syntactic shortcuts, the step element itself is providing the value.) The default namespace is never included in the namespace bindings for a variable, option or parameter value. Unqualified names are always in no-namespace. Unfortunately, in more complex situations, there may be no single variable, option or parameter that can reliably be expected to have the correct set of namespace bindings. Consider this pipeline: <p:pipeline type="ex:delete-in-div" xmlns:p="http://www.w3.org/ns/xproc" xmlns:ex="http://example.org/ns/ex" xmlns:h="http://www.w3.org/1999/xhtml"> <p:option name="divchild" required="true"/> <p:delete> <p:with-option name="match" select="concat('h:div/',$divchild)"/> </p:delete> </p:pipeline> It defines an atomic step (“ex:delete-in-div”) that deletes elements that occur inside of XHTML div elements. It might be used as follows: <ex:delete-in-div xmlns:p="http://www.w3.org/ns/xproc" xmlns:ex="http://example.org/ns/ex" xmlns:html="http://www.w3.org/1999/xhtml" divchild="html:p[@class='delete']"/> In this case, the match option passed to the p:delete step needs both the namespace binding of “h” specified in the ex:delete-in-div pipeline definition and the namespace binding of “html” specified in the divchild option on the call of that pipeline. It's not sufficient to provide just one of the sets of bindings. The p:namespaces element can be used as a child of p:variable, p:with-option or p:with-param to provide explicit bindings. The namespace bindings specified by a p:namespaces element are determined as follows: If the binding attribute is specified, it must contain the name of a single in-scope binding. The namespace bindings associated with that binding are used. It is a static error if the binding attribute on p:namespaces is specified and its value is not the name of an in-scope binding. If the element attribute is specified, it must contain an XPath expression which identifies a single element node (the input binding for this expression is the same as the binding for the p:option or p:with-param which contains it). The in-scope namespaces of that node are used. The expression is evaluated in the appropriate context, See . It is a dynamic error if the element attribute on p:namespaces is specified and it does not identify a single element node. If neither binding nor element is specified, the in-scope namespaces on the p:namespaces element itself are used. Irrespective of how the set of namespaces are determined, the except-prefixes attribute can be used to exclude one or more namespaces. The value of the except-prefixes attribute must be a sequence of tokens, each of which must be a prefix bound to a namespace in the in-scope namespaces of the p:namespaces element. All bindings of prefixes to each of the namespaces thus identified are excluded. It is a static error if the except-prefixes attribute on p:namespaces does not contain a list of tokens or if any of those tokens is not a prefix bound to a namespace in the in-scope namespaces of the p:namespaces element. It is a static error to specify both binding and element on the same p:namespaces element. If a p:variable, p:with-option or p:with-param includes one or more p:namespaces elements, then the union of all the namespaces specified on those elements are used as the bindings for the variable, option or parameter value. In this case, the in-scope namespaces on the p:variable, p:with-option or p:with-param are ignored. It is a dynamic error if the specified namespace bindings are inconsistent; that is, if the same prefix is bound to two different namespace names. For example, this would allow the preceding example to work: <p:pipeline type="ex:delete-in-div" xmlns:p="http://www.w3.org/ns/xproc" xmlns:ex="http://example.org/ns/ex" xmlns:h="http://www.w3.org/1999/xhtml"> <p:option name="divchild" required="true"/> <p:delete> <p:with-option name="match" select="concat('h:div/',$divchild)"> <p:namespaces xmlns:html="http://www.w3.org/1999/xhtml"/> </p:with-option> </p:delete> </p:pipeline> The p:namespaces element provides namespace bindings for both of the prefixes necessary to correctly interpret the expression ultimately passed to the p:delete step (the binding for html: is explicitly provided and the binding for h: is in-scope). The use of p:namespaces here, when all of the bindings are provided with explicit namespace declarations, is unnecessary. The bindings could simply be placed on the parent p:with-option element. We use p:namespaces here only to make the example parallel to the one which follows. The preceding solution has the weakness that it depends on knowing the bindings that will be used by the caller. A more flexible solution would use the binding attribute to copy the bindings from the caller's option value. <p:pipeline type="ex:delete-in-div" xmlns:p="http://www.w3.org/ns/xproc" xmlns:ex="http://example.org/ns/ex" xmlns:h="http://www.w3.org/1999/xhtml"> <p:option name="divchild" required="true"/> <p:delete> <p:with-option name="match" select="concat('h:div/',$divchild)"> <p:namespaces binding="divchild"/> <p:namespaces xmlns:h="http://www.w3.org/1999/xhtml"/> </p:with-option> </p:delete> </p:pipeline> This example will succeed as long as the caller-specified option does not bind the “h” prefix to something other than the XHTML namespace.

A p:declare-step provides the type and signature of an atomic step or pipeline. It declares the inputs, outputs, and options for all steps of that type. The value of the type can be from any namespace provided that the expanded-QName of the value has a non-null namespace URI. It is a static error if the expanded-QName value of the type attribute is in no namespace. Except as described in , the XProc namespace must not be used in the type of steps. Neither users nor implementers may define additional steps in the XProc namespace. Irrespective of the context in which the p:declare-step occurs, there are initially no option or variable names in-scope inside a p:declare-step. That is, p:option and p:variable elements can refer to values declared by their preceding siblings, but not by any of their ancestors. When a declared step is evaluated directly by the XProc processor (as opposed to occurring as an atomic step in some container), how the input and output ports are bound to documents is implementation-defined. A step declaration is not a step in its own right. Sibling steps cannot refer to the inputs or outputs of a p:declare-step using p:pipe; only instances of the type can be referenced. For a description of psvi-required, see . For xpath-version, see . For exclude-inline-prefixes, see p:inline.

When declaring an atomic step, the subpipeline in the declaration must be empty. And, conversely, if the subpipeline in a declaration is empty, the declaration must be for an atomic step. Implementations may use extension attributes to provide implementation-dependent information about a declared step. For example, such an attribute might identify the code which implements steps of this type. It is not an error for a pipeline to include declarations for steps that a particular processor does not know how to implement. It is, of course, an error to attempt to evaluate such steps. If p:log or p:serialization elements appear in the declaration of an atomic step, they will only be used if the atomic step is directly evaluated by the processor. They have no effect if the step appears in a subpipeline; only the serialization options of the “top level” step or pipeline are used because that is the only step which the processor is required to serialize.

When a p:declare-step declares a pipeline, that pipeline encapsulates the behavior of the specified subpipeline. Its children declare inputs, outputs, and options that the pipeline exposes and identify the steps in its subpipeline. The subpipeline may include declarations of additional steps (e.g., other pipelines or other step types that are provided by a particular implementation or in some implementation-defined way) and import other pipelines. If a pipeline has been imported, it may be invoked as a step within the subpipeline that imported it. The environment inherited by the subpipeline is the empty environment with these modifications: All of the declared inputs are added to the readable ports in the environment. If a primary input port is declared, that port is the default readable port, otherwise the default readable port is undefined. If a primary output port is declared and that port has no binding, then it is bound to the primary output port of the last step in the subpipeline. It is a static error if the primary output port has no binding and the last step in the subpipeline does not have a primary output port. The requested xpath-version must be used to evaluate XPath expressions subject to the constraints outlined in . The psvi-required attribute allows the author to declare that a step relies on the processor's ability to pass PSVI annotations between steps, see . If the attribute is not specified, the value “false” is assumed.

A p:library is a collection of step declarations and/or pipeline definitions. For a description of psvi-required, see . For xpath-version, see . For exclude-inline-prefixes, see p:inline. Libraries can import pipelines and/or other libraries. It is a static error if the import references in a pipeline or pipeline library are circular.

An p:import loads a pipeline or pipeline library, making it available in the pipeline or library which contains the p:import. An import statement loads the specified URI and makes any pipelines declared within it available to the current pipeline. It is a static error if the URI of a p:import cannot be retrieved or if, once retrieved, it does not point to a p:library, p:declare-step, or p:pipeline. It is a static error to import a single pipeline if that pipeline does not have a type. Attempts to retrieve the library identified by the URI value may be redirected at the parser level (for example, in an entity resolver) or below (at the protocol level, for example, via an HTTP Location: header). In the absence of additional information outside the scope of this specification within the resource, the base URI of the library is always the URI of the actual resource returned. In other words, it is the URI of the resource retrieved after all redirection has occurred. As imports are processed, a processor may encounter new p:import elements whose library URI is the same as one it has already processed in some other context. This may happen as a consequence of resolving the URI. If the actual base URI is the same as one that has already been processed, the implementation must recognize it as the same library and should not need to process the resource. Also, a duplicate, circular chain of imports, or a re-entrant import is not an error and implementations must take the necessary steps to avoid infinite loops and/or incorrect notification of duplicate step definitions. It is not an error for a library to import itself. An example of such steps is listed in . A library is considered the same library if the URI of the resource retrieved is the same. If a pipeline or library author uses two different URI values that resolve to the same resource, they must not be considered the same imported library. If the href URI, after being made absolute, begins “http://www.w3.org/YYYY/xproc-” (where YYYY is a four digit year), then it identifies the steps defined by a particular version of XProc. See . If the value is recognized by the processor, that is, if the processor understands the specified version, then the processor should not retrieve the library. It simply serves to identify the set of XProc steps that can be used without declaration. If the value is not recognized by the processor, then it must be retrieved and must point to a p:library. In such a library, and only in such a library, additional steps in the XProc namespace may be declared. It is a static error if a pipeline attempts to import two (or more) libraries with URIs that identify steps associated with a particular version of XProc. Processors may raise a static error if a library associated with a particular version of XProc is imported by a nested pipeline or library but is not also imported at the top level.

A p:pipe connects an input to a port on another step. The p:pipe element connects to a readable port of another step. It identifies the readable port to which it connects with the name of the step in the step attribute and the name of the port on that step in the port attribute. In all cases except the p:output of a compound step, it is a static error if the port identified by a p:pipe is not in the readable ports of the step that contains the p:pipe. A p:pipe that is a binding for an p:output of a compound step may connect to one of the readable ports of the compound step or to an output port on one of the compound step's contained steps. In other words, the output of a compound step can simply be a copy of one of the available inputs or it can be the output of one of its children.

A p:inline provides a document inline. The content of the p:inline element is wrapped in a document node and passed as input. The base URI of the document is the base URI of the p:inline element. It is a static error if the content of the p:inline element does not consist of exactly one element, optionally preceded and/or followed by any number of processing instructions, comments or whitespace characters. The in-scope namespaces of the inline document differ from the in-scope namespace of the content of the p:inline element in that bindings for all its excluded namespaces, as defined below, are removed: The XProc namespace itself (http://www.w3.org/ns/xproc) is excluded. A namespace URI designated by using an exclude-inline-prefixes attribute on the enclosing p:inline is excluded. A namespace URI designated by using an exclude-inline-prefixes attribute on any ancestor p:declare-step, p:pipeline, or p:library is also excluded. (In other words, the effect of exclude-inline-prefixes attributes is cumulative.) The value of each exclude-inline-prefixes attribute is interpreted as follows: The value of the attribute is either #all, or a whitespace-separated list of tokens, each of which is either a namespace prefix or #default. The namespace bound to each of the prefixes is designated as an excluded namespace. It is a static error if a namespace prefix is used within the exclude-inline-prefixes attribute and there is no namespace binding in scope for that prefix. The default namespace of the element on which exclude-inline-prefixes occurs may be designated as an excluded namespace by including #default in the list of namespace prefixes. It is a static error if the value #default is used within the exclude-inline-prefixes attribute and there is no default namespace in scope. The value #all indicates that all namespaces that are in scope for the element on which exclude-inline-prefixes occurs are designated as excluded namespaces.

A p:document reads an XML document from a URI. The document identified by the URI in the href attribute is loaded and returned. It is a dynamic error if the resource referenced by a p:document element does not exist, cannot be accessed, or is not a well-formed XML document. The parser which the p:document element employs must be conformant to Namespaces in XML. It must not fail on well-formed, standalone XML. The external subset should not be processed, but some parsers do not provide that option. It is implementation-defined whether or not the external subset is processed. Loading the document must not fail due to validation errors. It must not perform any other processing, such as expanding XIncludes. Use the p:load step if you need to perform DTD-based validation or wish to perform other processing on the document before it is used by a step.

A p:data reads an arbitrary resource from a URI. The resource identified by the URI in the href attribute is loaded, encoded, wrapped in the wrapper element, and returned as a document. If no wrapper element is specified, the default is c:data: It is a dynamic error if the document referenced by a p:data element does not exist, cannot be accessed, or cannot be encoded as specified. Exactly how the data is encoded depends on the media type of the resource. If the resource has a content type associated with it (e.g., if the resource was retrieved with HTTP), then that content type must be used, otherwise, if the user specified a content-type on the p:data, then that content type should be assumed. If no content type was specified or is associated with the resource, the inferred content type is implementation-dependent. If the media type of the response is an XML media type or text type with a charset parameter that is a Unicode character encoding (per ) or is recognized as a non-XML media type whose contents are encoded as a sequence of Unicode characters (e.g. it has a charset parameter or the definition of the media type is such that it requires Unicode), the data must be encoded as Unicode character sequence. If the media type is not an appropriate text type, or if the processor does not recognize the media type, the content is base64-encoded. The resulting encoded data is wrapped in an element with the name specified in the wrapper attribute (or c:data if no wrapper is specified). The wrapper element should have a content-type attribute which indicates the specified or inferred media type of the resource. If a content-type attribute is specified on a c:data wrapper, it must not be in a namespace; if the user-specified wrapper is not c:data, then the content-type attribute must be in the http://www.w3.org/ns/xproc-step namespace. Implementations may record additional details in extension attributes. For example, this p:identity step: <p:identity name="readcsv"> <p:input port="source"> <p:data href="stateabbr.csv"/> </p:input> </p:identity> might produce output like this: <c:data xmlns:c="http://www.w3.org/2007/03/xproc-step" content-type="text/plain"> AL,Alabama AK,Alaska AZ,Arizona … </c:data> Whereas this pipeline fragment: <p:identity name="readpng"> <p:input port="source"> <p:data href="icon.png" content-type="image/png"/> </p:input> </p:identity> <p:add-attribute name="makeimg" match="img" attribute-name="src"> <p:input port="source"><p:inline><img/></p:inline></p:input> <p:with-option name="attribute-value" select="concat('data:image/png;base64,',/*/node())"> <p:pipe step="readpng" port="result"/> </p:with-option> </p:add-attribute> produces a single img element with an inline graphic (represented using a data: URI): <img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAABmJLR0QA/wD/AP+gvaeTAAAACXBI WXMAAAsTAAALEwEAmpwYAAAAB3RJTUUH1QsEDycHOWjhgQAAAB10RVh0Q29tbWVudABDcmVhdGVk IHdpdGggVGhlIEdJTVDvZCVuAAABjklEQVQ4y42Tv0tbcRTFz3t5kuQFwUVFEYIGU6q4mU0RlCDR qYO2g4gdghUyKSFDwD/AwS2IoIMSHOLgpOLg4CIOWdy76GBoqQUJLlr66aCW6LuoF+7wvefcc3/w vZLgpbe0wOoqn/Ro5TKRVIpLi6tkkpoFpFJUj48JSVI2y4LnBTm+D1paYqa5OQiGw5DN8nV7m1hv L99f4o4Dk5Mc6Pwcd2yMXauL/n5+FAqsWdXjca5LJbokSXt7fOzu5toSaWsLxpqaIJcjr0ZbXGQh HDaWZPjQEGc7O3jPBC4u8EZHOXkruaODPxsbDMuylRWSra3cviYwO0upMcdtfNRqGq/X5esVu7nR BxMol4knEtTfGsH3+bu8zLdnydUqXjrN/nsWKEEiwdXmJp3/BYpFctFokOi6EIsF444DU1McSZLW 1+nq6eGnVWlkhNrcHBXXNUe5z+f5rEyGA8cxD+pufp7BYtH+yhL09fFbkYjd4vQ0W08jFgp8se7l wY3gwAC/KhXanwROTwlNTHBocf8BTQe7F9dc2bMAAAAASUVORK5CYII="/>

A p:empty binds to an empty sequence of documents.

A p:documentation contains human-readable documentation. There are no constraints on the content of the p:documentation element. Documentation is ignored by pipeline processors. See .

A p:pipeinfo contains ancillary information for steps in the pipeline. There are no constraints on the content of the p:pipeinfo element, see .

Errors in a pipeline can be divided into two classes: static errors and dynamic errors.

A static error is one which can be detected before pipeline evaluation is even attempted. Examples of static errors include cycles and incorrect specification of inputs and outputs. Static errors are fatal and must be detected before any steps are evaluated. For a complete list of static errors, see .

A A dynamic error is one which occurs while a pipeline is being evaluated. Examples of dynamic errors include references to URIs that cannot be resolved, steps which fail, and pipelines that exhaust the capacity of an implementation (such as memory or disk space). If a step fails due to a dynamic error, failure propagates upwards until either a p:try is encountered or the entire pipeline fails. In other words, outside of a p:try, step failure causes the entire pipeline to fail. For a complete list of dynamic errors, see .

Several of the steps in the standard and option step library can generate dynamic errors. For a complete list of the dynamic errors raised by builtin pipeline steps, see .

This section describes the standard XProc steps. A machine-readable description of these steps may be found in pipeline-library.xml. When a step in this library produces an output document, the base URI of the output is the base URI of the step's primary input document unless the step's process explicitly sets an xml:base attribute or the step's description explicitly states how the base URI is constructed. Also, in this section, several steps use this element for result information: When a step uses an XPath to compute an option value, the XPath context is as defined in . Several errors can be thrown by many steps; for convenience, they are summarized here: It is a dynamic error if the value supplied for any option specified for any step in this section is not of the type mandated in the step description, with phrases such as "The value of the some-name option must be a QName" or "the value of the some-flag option must be a boolean". In most steps which use a select expression or match pattern, any kind of node can be identified by the expression or pattern. However, some expressions and patterns on some steps are only applicable to some kinds of nodes (e.g., it doesn't make sense to speak of adding attributes to a comment!). It is a dynamic error if a select expression or match pattern returns a node type that is not allowed by the step.

This section describes standard steps that must be supported by any conforming processor.

The p:add-attribute step adds a single attribute to a set of matching elements. The input document specified on the source is processed for matches specified by the match pattern in the match option. For each of these matches, the attribute whose name is specified by the attribute-name option is set to the attribute value specified by the attribute-value option. The resulting document is produced on the result output port and consists of a exact copy of the input with the exception of the matched elements. Each of the match elements is copied to the output with the addition or change of the specified attribute name. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if the match pattern does not match an element. The value of the attribute-name option must be a QName. The corresponding expanded name is used to construct the added attribute. The value of the attribute-value option must be a legal attribute value according to XML. If an attribute with the same name as the expanded name from the attribute-name option exist on the matched element, the value specified in the attribute-value option is used to set the value of that existing attribute. That is, the value of the existing attribute is changed to the attribute-value value. If multiple attributes need to be set, the p:set-attributes step should be used. This step cannot be used to add namespace declarations. It is a dynamic error if the QName value in the attribute-name option uses the prefix 'xmlns' or any other prefix that resolves to the same namespace name as 'xmlns'.

The p:add-xml-base step exposes the base URI via explicit xml:base attributes. The input document from the source port is replicated to the result port with xml:base attributes added to or corrected on each element as specified by the options on this step. The value of the all option must be a boolean. The value of the relative option must be a boolean. It is a dynamic error if the all and relative options are both true. The p:add-xml-base step modifies its input as follows: For the document element: force the element to have an xml:base attribute with the document's [base URI] property's value as its value. For other elements: If the all option has the value true, force the element to have an xml:base attribute with the element's [base URI] value as its value. If the element's [base URI] is different from the its parent's [base URI], force the element to have an xml:base attribute with the following value: if the value of the relative option is true, a string which, when resolved against the parent's [base URI], will give the element's [base URI], otherwise the element's [base URI]. Otherwise, if there is an xml:base attribute present, remove it.

The p:compare step compares two documents for equality. The value of the fail-if-not-equal option must be a boolean. This step takes single documents on each of two ports and compares them using the fn:deep-equal (as defined in ). It is a dynamic error if the documents are not equal, and the value of the fail-if-not-equal option is true. If the documents are equal, or if the value of the fail-if-not-equal option is false, a c:result document is produced with contents true if the documents are equal, otherwise false.

The p:count step counts the number of documents in the source input sequence and returns a single document on result containing that number. The generated document contains a single c:result element whose contents is the string representation of the number of documents in the sequence. If the limit option is specified and is greater than zero, the p:count step will count at most that many documents. This provides a convenient mechanism to discover, for example, if a sequence consists of more than 1 document, without requiring every single document to be buffered before processing can continue.

The p:delete step deletes items specified by a match pattern from the source input document and produces the resulting document, with the deleted items removed, on the result port. The value of the match option must be an XSLTMatchPattern. A match pattern may match multiple items to be deleted. If an element is selected by the match option, the entire subtree rooted at that element is deleted.

The p:directory-list step produces a list of the contents of a specified directory. The value of the path option must be an anyURI. It is interpreted as an IRI reference. If it is relative, it is made absolute against the base URI of the element on which it is specified (p:with-option or p:directory-list in the case of a syntactic shortcut value). It is a dynamic error if the absolute path does not identify a directory. It is a dynamic error if the contents of the directory path are not available to the step due to access restrictions in the environment in which the pipeline is run. Conformant processors must support directory paths whose scheme is file. It is implementation-defined what other schemes are supported by p:directory-list, and what the interpretation of 'directory', 'file' and 'contents' is for those schemes. If present, the value of the include-filter or exclude-filter option must be a regular expression as specified in , section 7.61 “Regular Expression Syntax”. If the include-filter pattern matches a directory entry's name, the entry is included in the output. If the exclude-filter pattern matches a directory entry's name, the entry is excluded in the output. If both options are provided, the include filter is processed first, then the exclude filter. The result document produced for the specified directory path has a c:directory document element whose base URI is the directory path and whose name attribute is the last segment of the directory path (that is, the directory's (local) name). Its contents are determined as follows, based on the entries in the directory identified by the directory path. For each entry in the directory, if either no filter was specified, or the (local) name of the entry matches the filter pattern, a c:file, a c:directory, or a c:other element is produced, as follows: A c:directory is produced for each subdirectory not determined to be special. A c:file is produced for each file not determined to be special. Any file or directory determined to be special by the p:directory-list step may be output using a c:other element but the criteria for marking a file as special are implementation-defined. When a directory entry is a subdirectory, that directory's entries are not output as part of that entry's c:directory. A user must apply this step again to the subdirectory to list subdirectory contents. Each of the elements c:file, c:directory, and c:other has a name attribute when it appears within the top-level c:directory element, whose value is a relative IRI reference, giving the (local) file or directory name. Any attributes other than name on c:file, c:directory, or c:other are implementation-defined.

The c:error step generates a dynamic error using the input provided to the step. The value of the code option must be a QName This step uses the document provided on its input as the content of the error raised. Since it generates an error upon invocation, there can be no normal output; instead, an instance of the c:errors element will be produced on the error output port, as is always the case for dynamic errors. The error generated can be caught by a p:try just like any other dynamic error. For example, given the following invocation: The document element is unknown. ]]> The error vocabulary element (and document) generated on the error output port would be: The document element is unknown. ]]> The href, line and column, or offset, might also be present on the c:error to identify the location of the p:error element in the pipeline.

The p:escape-markup step applies XML serialization to the children of the document element and replaces those children with their serialization. The outcome is a single element with text content that represents the "escaped" syntax of the children as they were serialized. &serialization-options-for-escape-markup; This step supports the standard serialization options as specified in . These options control how the output markup is produced before it is escaped. For example, the input: <description> <div xmlns="http://www.w3.org/1999/xhtml"> <p>This is a chunk of XHTML.</p> </div> </description> produces: <description> &lt;div xmlns="http://www.w3.org/1999/xhtml"> &lt;p>This is a chunk of XHTML.&lt;/p> &lt;/div> </description> The result of this step is an XML document that contains the Unicode characters that are the characters that result from escaping the input. It is not encoded characters in a serialized octet stream, therefore, the serialization options related to encoding characters (byte-order-mark, encoding, and normalization-form) do not apply. They are omitted from the standard serialization options on this step. Since the result of this step is represented by Unicode characters in the document produced by this step and not as encoded characters serialized into a byte stream, the option normalization-form does not apply to this step and has been omitted from the standard serialization options. By default, this step must not generate an XML declaration in the escaped result.

The p:filter step selects portions of the source document based on a (possibly dynamically constructed) XPath select expression. This step behaves just like an p:input with a select expression except that the select expression is computed dynamically.

The p:http-request step provides for interaction with resources over HTTP or related protocols. The input document provided on the source port specifies a request by a single c:request element. This element specifies the method, resource, and other request properties as well as possibly including an entity body (content) for the request. &serialization-options; The standard serialization options are provided to control the serialization of any XML content which is sent as part of the request. The effect of these options is as specified in . See for a discussion of when serialization occurs in constructing a request. It is a dynamic error if the document element of the document that arrives on the source port is not c:request.

A HTTP request is represented by a c:request element. It is a dynamic error if the request contains a c:body or c:multipart but the method does not allow for an entity body being sent with the request. It is a dynamic error if the status-only attribute has the value true and the detailed attribute does not have the value true. The method attribute specifies the method to be used against the IRI specified by the href attribute, e.g. GET or POST. If the href attribute is not absolute, it will be resolved against the base URI of the element on which it is occurs. In the case of simple “GET” requests, implementors are encouraged to support as many protocols as practical. In particular, pipeline authors may attempt to use p:http-request to load documents with computed URIs using the file: scheme. If the username attribute is specified, the username, password, auth-method, and send-authorization attributes are used to handle authentication as per . If the initial response to the request is an authentication challenge, the username and password attribute values are used to generate an Authorization header and the request is sent again. If that authorization fails, the request is not retried. For the purposes of avoiding an authentication challenge, if the send-authorization attribute has a value of true and the authentication method specified by the auth-method supports generation of an Authorization header without a challenge, then an Authorization header is generated and sent on the first request. If the response contains an authentication challenge, the request is retried with an appropriate Authorization header. Appropriate values for the auth-method attribute are "Basic" or "Digest" but other values are allowed. The interpretation of auth-method values on c:request other than “Basic” or “Digest” is implementation-defined. It is a dynamic error if a username or password is specified without specifying an auth-method, if the requested auth-method isn't supported, or the authentication challenge contains an authentication method that isn't supported. All implementations are required to support "Basic" and "Digest" authentication per . The c:header element specifies a header name and value, either for inclusion in a request, or as received in a response. The request is formulated from the attribute values on the c:request element and its c:header and c:multipart or c:body children, if present, and transmitted to the host (and port, if present) specified by the href attribute. The details of how the request entity body, if any, is constructed are given in the next section. When the request is formulated, the step and/or protocol implementation may add headers as necessary to either complete the request or as appropriate for the content specified (e.g. transfer encodings). A user of this step is guaranteed that their requested headers and content will be sent with the exception of any conflicts with protocol-related headers. It is a dynamic error if the value of a header specified via c:header (e.g. Content-Type) conflicts with the value for that header that the step and/or protocol implementation must set.

The c:multipart element specifies a multi-part body, per , either for inclusion in a request or as received in a response. In the context of a request, the media type of the c:multipart must be a multipart media type (i.e. have a main type of 'multipart'). If the content-type attribute is not specified, a value of "multipart/mixed" will be assumed. The boundary attribute is required and is used to provide a multipart boundary marker. The implementation must use this boundary marker and must prefix the value with the string “--” when formulating the multipart message. It is a dynamic error if the value starts with the string “--”. In a multipart message, the first set of c:header elements that are the children of c:request are the headers to the multipart message. The headers inside the c:multipart element are associated with a particular message part. Each multipart body is represented by a c:body preceded by some number of c:header elements. These preceding headers associated with the body part in the multipart message. The c:body element holds the body or body part of the message. Each of the attributes holds controls some aspect of the encoding the request body or decoding the body element's content when the request is formulated. These are specified as follows: The content-type attribute specifies the media type of the body or body part, that is, the value of its Content-Type header. If the media type is not an XML type or text, the content must already be base64-encoded. The encoding attribute controls the decoding of the element content for formulating the body. A value of base64 indicates the element's content is a base64 encoded string whose byte stream should be sent as the message body. An implementation may support other encodings other that base64 but these encodings and their names are implementation-defined. It is a dynamic error if the encoding specified is not supported by the implementation. The id attribute specifies the value of the Content-ID header for the body or body part. The description attribute specifies the value of the Content-Description header for the body or body part. If an entity body is to be sent as part of a request (e.g. a POST), either a c:body element, specifying the request entity body, or a c:multipart element, specifying multiple entity body parts, may be used. When c:multipart is used it may contain multiple c:body children. A c:body specifies the construction of a body or body part as follows: If the content-type attribute does not specify an XML media type, or the encoding attribute is “base64”, then it is a dynamic error if the content of the c:body element does not consist entirely of characters, and the entity body or body part will consist of exactly those characters. Otherwise (the content-type attribute does specify an XML media type and the encoding attribute is not 'base64'), it is a dynamic error if the content of the c:body element does not consist of exactly one element, optionally preceded and/or followed by any number of processing instructions, comments or whitespace characters, and the entity body or body part will consist of the serialization of a document node containing that content. The serialization of that document is controlled by the serialization options on the p:http-request step itself. For example, the following input to a p:http-request step will POST a small XML document: ]]> The corresponding request should look something like this: ]]>

The handling of the response to the request and the generation of the step's result document is controlled by the status-only, override-content-type and detailed attributes on the c:request input. The override-content-type attribute controls interpretation of the response's Content-Type header. If this attribute is present, the response will be treated as if it returned the Content-Type given by its value. This original Content-Type header will however be reflected unchanged as a c:header in the result document. It is a dynamic error if the override-content-type value cannot be used (e.g. text/plain to override image/png). If the status-only attribute has the value true, the result document will contain only header information. The entity of the response will not be processed to produce a c:body or c:multipart element. The c:response element represents an HTTP response. The response's status code is encoded in the status attribute and the headers and entity body are processing into c:header and c:multipart or c:body content. The value of the detailed attribute determines the content of the result document. If it is true, the response to the request is handled as follows: A single c:response element is produced with the status attribute containing the status of the response received. Each response header is translated into a c:header element. Unless the status-only attribute has a value true, the entity body of the response is converted into a c:body or c:multipart element via the rules given in the next section. Otherwise (the detailed attribute is not specified or its value is false), the response to the request is handled as follows: If the media type (as determined by the override-content-type attribute or the Content-Type response header) is an XML media type, the entity is decoded if necessary, then parsed as an XML document and produced on the result output port as the entire output of the step. Otherwise, the entity body of the response is converted into a c:body or c:multipart element via the rules given in the next section. In either case the base URI of the output document is the resolved value of the href attribute from the input c:request.

The entity of a response may be multipart per . In those situations, the result document will be a c:multipart element that contains multiple c:body elements inside. Although it is technically possible for any of the individual parts of a multipart message to also be multipart, XProc does not provide a standard representation for such messages. The interpretation of a multipart message inside another multipart message is implementation-dependent. If the media type of the response is an XML media type or text type with a charset parameter that is a Unicode character encoding (per ) or is recognized as a non-XML media type whose contents are encoded as a sequence of Unicode characters (e.g. it has a character parameter or the definition of the media type is such that it requires Unicode), the content of the constructed c:body element is the translation of the text into a Unicode character sequence. If the media type of the response is an XML media type, the content of the constructed c:body element is the result of decoding the body if necessary, then parsing it with an XML parser. If the content is not well-formed, the step fails. For all other media types, the response is encoded as base64 (unless it is encoded already) and then produced as text children of the c:body element. If the content is base64-encoded, the encoding attribute on c:body must be set to “base64”. In the case of a multipart response, the same rules apply when constructing a c:body element for each body part encountered. Given the above description, any content identified as text/html will be encoded as (escaped) text or base64-encoded in the c:body element, as HTML isn't always well-formed XML. A user can attempt to convert such content into XML using the p:unescape-markup step.

A simple form might be posted as follows: <c:http-request method="POST" href="http://www.example.com/form-action" xmlns:c="http://www.w3.org/ns/xproc-step"> <c:body content-type="application/x-www-form-urlencoded"> name=W3C&amp;spec=XProc </c:body> </c:http-request> and if the response was an XHTML document, the result document would be: <c:http-response status="200" xmlns:c="http://www.w3.org/ns/xproc-step"> <c:header name="Date" value=" Wed, 09 May 2007 23:12:24 GMT"/> <c:header name="Server" value="Apache/1.3.37 (Unix) PHP/4.4.5"/> <c:header name="Vary" value="negotiate,accept"/> <c:header name="TCN" value="choice"/> <c:header name="P3P" value="policyref='http://www.w3.org/2001/05/P3P/p3p.xml'"/> <c:header name="Cache-Control" value="max-age=600"/> <c:header name="Expires" value="Wed, 09 May 2007 23:22:24 GMT"/> <c:header name="Last-Modified" value="Tue, 08 May 2007 16:10:49 GMT"/> <c:header name="ETag" value="'4640a109;42380ddc'"/> <c:header name="Accept-Ranges" value="bytes"/> <c:header name="Keep-Alive" value="timeout=2, max=100"/> <c:header name="Connection" value="Keep-Alive"/> <c:body content-type="application/xhtml+xml"> <html xmlns="http://www.w3.org/1999/xhtml"> <head><title>OK</title></head> <body><p>OK!</p></body> </html> </c:body> </c:http-response>

The p:identity step makes a verbatim copy of its input available on its output. If the implementation supports passing PSVI annotations between steps, the p:identity step must preserve any annotations that appear in the input.

The p:insert step inserts the insertion port's document into the source port's document relative to the matching elements in the source port's document. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if that pattern matches anything other than element, text, processing-instruction, or comment nodes. Multiple matches are allowed, in which case multiple copies of the insertion documents will occur. If no elements match, then the document is unchanged. The value of the position option must be an NMTOKEN in the following list: ”first-child” - the insertion is made as the first child of the match; ”last-child” - the insertion is made as the last child of the match; ”before” - the insertion is made as the immediate preceding sibling of the match; ”after” - the insertion is made as the immediate following sibling of the match. It is a dynamic error if the match pattern matches anything other than an element node and the value of the position option is “first-child” or “last-child”. As the inserted elements are part of the output of the step they are not considered in determining matching elements. If an empty sequence appears on the insertion port, the result will be the same as the source.

The p:label-elements step generates a label for each matched element and stores that label in the specified attribute. The value of the attribute option must be a QName. The value of the label option is an XPath expression used to generate the value of the attribute label. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if that expression matches anything other than element nodes. The value of the replace must be a boolean value and is used to indicate whether existing attribute values are replaced. This step operates by generating attribute labels for each element matched. For every matched element, the expression is evaluated with the context node set to the matched element. An attribute is added to the matched element using the attribute name is specified the attribute option and the string value of result of evaluating the expression. If the attribute already exists on the matched element, the value is replaced with the string value of the expression evaluation result only if the replace option has the value of true. An implementation must bind the variable “p:index” in the static context of each evaluation of the XPath expression to the position of the element in the sequence of matched elements. In other words, the first element (in document order) matched gets the value “1”, the second gets the value “2”, the third, “3”, etc. The result of the p:label-elements step is the input document with the attribute labels associated with matched elements. All other non-matching content remains the same.

The p:load step has no inputs but produces as its result an XML resource specified by an IRI. The value of the href option must be an anyURI. It is interpreted as an IRI reference. If it is relative, it is made absolute against the base URI of the element on which it is specified (p:with-option or p:load in the case of a syntactic shortcut value). The value of the dtd-validate option must be a boolean. Load attempts to read an XML document from the specified IRI reference, which may be relative, in which case it will be resolved relative to the base URI of the element on which it is specified (p:option or p:load in the case of a syntactic shortcut value). It is a dynamic error if the document does not exist or is not well-formed. It is a dynamic error if the step is not allowed to retrieve from the specified location. Otherwise, the retrieved document is produced on the result port. The base URI of the result is the (absolute) IRI used to retrieve it. If the value of the dtd-validate option is true, DTD validation is performed on the retrieved document. It is a dynamic error if the document is not valid or the step doesn't support DTD validation.

The p:make-absolute-uris step makes an element or attribute's value in the source document an absolute IRI value in the result document. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if the pattern matches anything other than element or attribute nodes. The value of the base-uri option must be an anyURI. It is interpreted as an IRI reference. If it is relative, it is made absolute against the base URI of the element on which it is specified (p:with-option or p:make-absolute-uris in the case of a syntactic shortcut value). For every element or attribute in the input document which matches the specified pattern, its XPath string-value is resolved against the specified base URI and the resulting absolute IRI is used as the matched node's entire contents in the output. The base URI used for resolution defaults to the matched attribute's element or the matched element's base URI unless the base-uri option is specified. When the base-uri option is specified, the option value is used as the base URI regardless of any contextual base URI value in the document. This option value is resolved against the base URI of the p:option element used to set the option. If the IRI reference specified by the base-uri option on p:make-absolute-uris is not valid, or if it is absent and the input document has no base URI, the results are implementation-dependent.

The p:namespace-rename step renames any namespace declaration or use of a namespace in a document to a new IRI value. The value of the from option must be an anyURI. It should be either empty or absolute, but will not be resolved in any case. The value of the to option must be an anyURI. It should be empty or absolute, but will not be resolved in any case. The value of the apply-to option must be one of “all”, “elements”, or “attributes”. If the value is “elements”, only elements will be renamed, if the value is “attributes”, only attributes will be renamed, if the value is “all”, both elements and attributes will be renamed. It is a dynamic error if the XML namespace (http://www.w3.org/XML/1998/namespace) or the XMLNS namespace (http://www.w3.org/2000/xmlns/) is the value of either the from option or the to option. If the value of the from option is the same as the value of the to option, the input is reproduced unchanged on the output. Otherwise, namespace bindings, namespace attributes and element and attribute names are changed as follows: Namespace bindings: If the from option is present and its value is not the empty string, then every binding of a prefix (or the default namespace) in the input document whose value is the same as the value of the from option is replaced in the output with a binding to the value of the to option, provided it is present and not the empty string; otherwise (the to option is not specified or has an empty string as its value) absent from the output. If the from option is absent, or its value is the empty string, then no bindings are changed or removed. Elements and attributes: If the from option is present and its value is not the empty string, for every element and attribute, as appropriate, in the input whose namespace name is the same as the value of the from option, in the output its namespace name is replaced with the value of the to option, provided it is present and not the empty string; otherwise (the to option is not specified or has an empty string as its value) changed to have no value. If the from option is absent, or its value is the empty string, then for every element and attribute, as appropriate, whose namespace name has no value, in the output its namespace name is set to the value of the to option. Namespace attributes: If the from option is present and its value is not the empty string, for every namespace attribute in the input whose value is the same as the value of the from option, in the output the namespace attribute's value is replaced with the value of the to option, provided it is present and not the empty string; otherwise (the to option is not specified or has an empty string as its value) the namespace attribute is absent. The apply-to option is primarily intended to make it possible to avoid renaming attributes when the from option specifies no namespace, since many attributes are in no namespace. Care should be taken when specifying no namespace with the to option. Prefixed names in content, for example QNames and XPath expressions, may end up with no appropriate namespace binding.

The p:pack step merges two document sequences in a pair-wise fashion. The value of the wrapper option must be a QName. The step takes each pair of documents, in order, one from the source port and one from the alternate port, wraps them with a new element node whose QName is the value specified in the wrapper option, and writes that element to the result port as a document. If the step reaches the end of one input sequence before the other, then it simply wraps each of the remaining documents in the longer sequence. In the common case, where the document element of a document in the result sequence has two element children, any comments, processing instructions, or white space text nodes that occur between them may have come from either of the input documents; this step does not attempt to distinguish which one.

The p:parameters step exposes a set of parameters as a c:param-set document. Each parameter passed to the step is converted into a c:param element. The step resolves duplicate parameters in the normal way (see ) so at most one parameter with any given name will appear in the result. The resulting c:param elements are wrapped in a c:param-set and the parameter set document is written to the result port. The order in which c:param elements occur in the c:param-set is implementation-dependent. For consistency and user convenience, if any of the parameters have names that are in a namespace, the namespace attribute on the c:param element must be used. Each name must be an NCName. The base URI of the output document is the URI of the pipeline document that contains the step. Since the parameters port is not primary, any explicit p:with-param settings must include a port attribute, per the last paragraph of .

The p:rename step renames elements, attributes, or processing-instruction targets in a document. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if the pattern matches anything other than element, attribute or processing instruction nodes. The value of the new-name option must be a QName. Each element, attribute, or processing-instruction in the input matched by the match pattern specified in the match option is renamed in the output to the name specified by the new-name option. If the pattern matches processing instructions, then it is the processing instruction target that is renamed. It is a dynamic error if the pattern matches a processing instruction and the new name has a non-null namespace.

The p:replace step replaces matching elements in its primary input with the document element of the replacement port's document. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if that pattern matches anything other than element, text, processing-instruction, or comment nodes. Multiple matches are allowed, in which case multiple copies of the replacement document will occur. Every element in the primary input matching the specified pattern is replaced in the output is replaced by the document element of the replacement document. Only non-nested matches are replaced. That is, once an element is replaced, its descendants cannot be matched.

The p:set-attributes step sets attributes on matching elements. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if that pattern matches anything other than element nodes. Each attribute on the document element of the document that appears on the attributes port is copied to each element that matches the match expression. If an attribute with the same name as one of the attributes to be copied already exists, the value specified on the attribute port's document is used. The result port of this step produces a copy of the source port's document with the matching elements' attributes modified. The matching elements are specified by the match pattern in the match option. All matching elements are processed. If no elements match, the step will not change any elements. This step must not copy namespace declarations. If the attributes copied from the attributes use namespaces, prefixes, or prefixes bound to different namespaces, the document produced on the result output port will require namespace fixup.

The p:sink step accepts a sequence of documents and discards them. It has no output.

The p:split-sequence step accepts a sequence of documents and divides it into two sequences. The value of the test option must be an XPathExpression. The XPath expression in the test option is applied to each document in the input sequence. If the effective boolean value of the expression is true, the document is copied to the matched port; otherwise it is copied to the not-matched port. If the initial-only option is true, then when the first document that does not satisfy the test expression is encountered, it and all the documents that follow it are written to the not-matched port. In other words, it only writes the initial series of matched documents (which may be empty) to the matched port. All other documents are written to the not-matched port, irrespective of whether or not they match. The XPath context for the test option changes over time. For each document that appears on the source port, the expression is evaluated with that document as the context document. The context position (position()) is the position of that document within the sequence and the context size (last()) is the total number of documents in the sequence. In principle, this component cannot stream because it must buffer all of the input sequence in order to find the context size. In practice, if the test expression does not use the last() function, the implementation can stream and ignore the context size. If the implementation supports passing PSVI annotations between steps, the p:split-sequence step must preserve any annotations that appear in the input.

The p:store step stores a serialized version of its input to a URI. This step outputs a reference to the location of the stored document. &serialization-options; The value of the href option must be an anyURI. If it is relative, it is made absolute against the base URI of the element on which it is specified (p:with-option or p:store in the case of a syntactic shortcut value). The step attempts to store the XML document to the specified URI. It is a dynamic error if the URI scheme is not supported or the step cannot store to the specified location. The output of this step is a document containing a single c:result element whose content is the absolute URI of the document stored by the step. The standard serialization options are provided to control the serialization of the XML content when it is stored. These options are as specified in .

The p:string-replace step matches nodes in the document provided on the source port and replaces them with the string result of evaluating an XPath expression. The value of the match option must be an XSLTMatchPattern. The value of the replace option must be an XPathExpression. The matched nodes are specified with the match pattern in the match option. For each matching node, the XPath expression provided by the replace option is evaluated and the string value of the result is used in the output. Nodes that do not match are copied without change. If the expression given in the match option matches an attribute, the string value of the replace expression is used as the new value of the attribute in the output. If the expression matches any other kind of node, the entire node (and not just its contents) is replaced by the string value of the replace expression.

The p:unescape-markup step takes the string value of the document element and parses the content as if it was a Unicode character stream containing serialized XML. The output consists of the same document element with children that result from the parse. This is the reverse of the p:escape-markup step. The value of the namespace option must be an anyURI. It should be absolute, but will not be resolved. When the string value is parsed, the original document element is preserved so that the result will be well-formed XML even if the content consists of multiple, sibling elements. The namespace option specifies the default namespace. If it is provided, it will be declared as the default namespace on the document element. The content-type option may be used to specify an alternate content type for the string value. An implementation may use a different parser to produce XML content depending on the specified content-type. For example, an implementation might provide an HTML to XHTML parser (e.g. or ) for the content type 'text/html'. All implementations must support the content type application/xml, and must use a standard XML parser for it. It is a dynamic error if the content-type specified is not supported by the implementation. Behavior of p:unescape-markup for content-types other than application/xml is implementation-defined. The encoding option specifies how the data is encoded. All implementations must support the base64 encoding (and the absence of an encoding option, which implies that the content is plain Unicode text). It is a dynamic error if the encoding specified is not supported by the implementation. If an encoding is specified, a charset may also be specified. The octet-stream that results from decoding the text must be interpreted using the encoding named by the value of the charset option to produce a sequence of Unicode characters to parse. The character set may be specified as a parameter on the content-type or via the separate charset option. If it is specified in both places, the value of the charset option must be used. If no encoding is specified, the character set is ignored, irrespective of where it was specified. It is a dynamic error if an encoding of “base64” is specified and a character set is not, or if the specified character set is not supported by the implementation. For example, with the 'namespace' option set to the XHTML namespace, the following input: <description> &lt;p>This is a chunk.&lt;/p> &lt;p>This is a another chunk.&lt;/p> </description> would produce: <description> <p xmlns="http://www.w3.org/1999/xhtml">This is a chunk.</p> <p xmlns="http://www.w3.org/1999/xhtml">This is a another chunk.</p> </description>

The p:unwrap step replaces matched elements with their children. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if that pattern matches anything other than element nodes. Every element in the source document that matches the specified match pattern is replaced by its children, effectively “unwrapping” the children from their parent. Non-element nodes and unmatched elements are passed through unchanged. The matching applies to the entire document, not just the “top-most” matches. A pattern of the form h:div will replace all h:div elements, not just the top-most ones. This step produces a single document; if the document element is unwrapped, the result might not be well-formed XML.

The p:wrap step wraps matching nodes in the source document with a new parent element. The value of the wrapper option must be a QName. The value of the match option must be an XSLTMatchPattern. It is a dynamic error if the pattern matches anything other than document, element, text, processing instruction, and comment nodes. The value of the group-adjacent option must be an XPathExpression. If the node matched is the document node (match="/"), the result is a new document where the document element is a new element node whose QName is the value specified in the wrapper option. That new element contains copies of all of the children of the original document node. When the match pattern does not match the document node, every node that matches the specified match pattern is replaced with a new element node whose QName is the value specified in the wrapper option. The content of that new element is a copy of the original, matching node. The group-adjacent option can be used to group adjacent matching nodes in a single wrapper element. The specified XPath expression is evaluated for each matching node with that node as the XPath context node. Whenever two or more adjacent matching nodes have the same “group adjacent” value, they are wrapped together in a single wrapper element. Two matching nodes are considered adjacent if and only if they are siblings and either there are no nodes between them or all intervening, non-matching nodes are whitespace text, comment, or processing instruction nodes.

The p:wrap-sequence step accepts a sequence of documents and produces either a single document or a new sequence of documents. The value of the wrapper option must be a QName. The value of the group-adjacent option must be an XPathExpression. In its simplest form, p:wrap-sequence takes a sequence of documents and produces a single, new document by placing each document in the source sequence inside a new document element as sequential siblings. The name of the document element is the value specified in the wrapper option. The group-adjacent option can be used to group adjacent documents. The XPath context for the group-adjacent option changes over time. For each document that appears on the source port, the expression is evaluated with that document as the context document. The context position (position()) is the position of that document within the sequence and the context size (last()) is the total number of documents in the sequence. Whenever two or more sequentially adjacent documents have the same “group adjacent” value, they are wrapped together in a single wrapper element.

The p:xinclude step applies processing to the source document. The value of the fixup-xml-base option must be a boolean. If it is true, base URI fixup will be performed as per . The value of the fixup-xml-lang option must be a boolean. If it is true, language fixup will be performed as per . The included documents are located with the base URI of the input document and are not provided as input to the step. It is a dynamic error if an XInclude error occurs during processing.

The p:xslt step applies an or stylesheet to a document. If present, the value of the initial-mode option must be a QName. If present, the value of the template-name option must be a QName. If present, the value of the output-base-uri option must be an anyURI. If it is relative, it is made absolute against the base URI of the element on which it is specified (p:with-option or p:xslt in the case of a syntactic shortcut value). If the step specifies a version, then that version of XSLT must be used to process the transformation. It is a dynamic error if the specified version of XSLT is not available. If the step does not specify a version, the implementation may use any version it has available and may use any means to determine what version to use, including, but not limited to, examining the version of the stylesheet. The XSLT stylesheet provided on the stylesheet port is applied to the document on the source port. Any parameters passed on the parameters port are used to define top-level stylesheet parameters. The primary result document of the transformation appears on the result port. All other result documents appear on the secondary port. If XSLT 1.0 is used, an empty sequence of documents must appear on the secondary port. If a sequence of documents is provided on the source port, the first document is assumed to be the primary input document. This sequence is also the default collection. It is a dynamic error if a sequence of documents is provided to an XSLT 1.0 step. A dynamic error occurs if the XSLT processor signals a fatal error. This includes the case where the transformation terminates due to a xsl:message instruction with a terminate attribute value of “yes”. How XSLT message termination errors are reported to the XProc processor is implementation-dependent. The invocation of the transformation is controlled by the initial-mode and template-name options that set the initial mode and/or named template in the XSLT transformation where processing begins. It is a dynamic error if the specified initial mode or named template cannot be applied to the specified stylesheet. The output-base-uri option sets the context's output base URI per the XSLT 2.0 specification, otherwise the base URI of the result document is the base URI of the first document in the source port's sequence. If the value of the output-base-uri option is not absolute, it will be resolved using the base URI of its p:option element. An XSLT 1.0 step should use the value of the output-base-uri as the base URI of its output, if the option is specified. If XSLT 2.0 is used, the outputs of this step may include PSVI annotations. The static and initial dynamic contexts of the XSLT processor are the contexts defined in for an XSLT 1.0 processor and for an XSLT 2.0 processor with the following adjustments. The dynamic context is augmented as follows: Context item The first document that appears on the source port. Variable values Any parameters passed on the parameters port are available as variable bindings to the XSLT processor. Function implementations The function implementations provided by the XSLT processor. Default collection The sequence of documents provided on the source port.

The following steps are optional. If they are supported by a processor, they must conform to the semantics outlined here, but a conformant processor is not required to support all (or any) of these steps.

The p:exec step runs an external command passing the input that arrives on its source port as standard input, reading result from standard output, and errors from standard error. &serialization-options; The values of the command, args and cwd options must be a string. The values of the source-is-xml, result-is-xml, errors-is-xml, and fix-slashes options must be boolean. The p:exec step executes the command passed on command with the arguments passed on args. The processor does not interpolate the values of the command or args (for example, expanding references to environment variables). It is a dynamic error if the command cannot be run. If cwd is specified, then the current working directory is changed to the value of that option before execution begins. It is a dynamic error if the current working directory cannot be changed to the value of the cwd option. If cwd is not specified, the current working directory is implementation-defined. If the command or cwd options contain any “/” or “\” characters, they will be replaced with the platform-specific path separator character. If the fix-slashes option is true, this fixup will be applied to args as well. The document that arrives on the source port will be passed to the command as its standard input. If source-is-xml is true, the serialization options are used to convert the input into serialized XML which is passed to the command, otherwise the XPath string-value of the document is passed. The standard output of the command is read and returned on result; the standard error output is read and returned on errors. In order to assure that the result will be an XML document, each of the results will be wrapped in a c:result element. If result-is-xml is true, the standard output of the program is assumed to be XML and will be parsed as a single document. If it is false, the output is assumed not to be XML and will be returned as escaped text. If wrap-result-lines is true, a c:line element will be wrapped around each line of output. It is a dynamic error to specify both result-is-xml and wrap-result-lines. The same rules apply to the standard error output of the program, with the errors-is-xml and wrap-error-lines options, respectively. If either of the results are XML, they must be parsed with namespaces enabled and validation turned off, just like p:document. The single args option is treated as a series of whitespace-separated values. Values which contain spaces may be quoted with either single (') or double (") quotes. A literal quote character may be inserted by doubling it.

The p:hash step generates a hash, or digital “fingerprint”, for some value and injects it into the source document. The value of the algorithm option must be a QName. If it does not have a prefix, then it must be one of the following values: “crc”, “md”, or “sha”. If a version is not specified, the default version is algorithm-defined. For “crc” it is 32, for “md” it is 5, for “sha” it is 1. A hash is constructed from the string specified in the value option using the specified algorithm and version. Implementations must support , , and hashes. It is implementation-defined what other algorithms are supported. The resulting hash should be returned as a string of hexidecimal characters. The value of the match option must be an XSLTMatchPattern. The hash of the specified value is computed using the algorithm and parameters specified. It is a dynamic error if the requested hash algorithm is not one that the processor understands or if the value or parameters are not appropriate for that algorithm. The matched nodes are specified with the match pattern in the match option. For each matching node, the string value of the computed hash is used in the output. Nodes that do not match are copied without change. If the expression given in the match option matches an attribute, the hash is used as the new value of the attribute in the output. If the expression matches any other kind of node, the entire node (and not just its contents) is replaced by the hash.

The p:uuid step generates a and injects it into the source document. The value of the match option must be an XSLTMatchPattern. The value of the version option must be an integer. If the version is specified, that version of UUID must be computed. It is a dynamic error if the processor does not support the specified version of the UUID algorithm. If the version is not specified, the version of UUID computed is implementation-defined. The matched nodes are specified with the match pattern in the match option. For each matching node, the generated UUID is used in the output. Nodes that do not match are copied without change. If the expression given in the match option matches an attribute, the UUID is used as the new value of the attribute in the output. If the expression matches any other kind of node, the entire node (and not just its contents) is replaced by the UUID.

The p:validate-with-relax-ng step applies validation to the source document. The values of the dtd-attribute-values and dtd-id-idref-warnings options must be booleans. If the root element of the schema is c:data or has a c:content-type attribute that specifies a text content type or a media type that the implementation recognizes, then the step should treat the text node descendants of the element as a document for validation. If the dtd-attribute-values option is true, then the attribute value defaulting conventions of are also applied. If the dtd-id-idref-errors option is true, then the validator should treat a schema that is incompatible with the ID/IDREF/IDREFs feature of as if the document was invalid. It is a dynamic error if the assert-valid option is true and the input document is not valid. The output from this step is a copy of the input, possibly augmented by application of the . The output of this step may include PSVI annotations. Support for is implementation defined.

The p:validate-with-schematron step applies processing to the source document. It is a dynamic error if the assert-valid option is true and any Schematron assertions fail. The value of the phase option identifies the Schematron validation phase with which validation begins. The parameters port provides name/value pairs which correspond to Schematron external variables. The result output from this step is a copy of the input. Schematron assertions and reports, if any, must appear on the report port. The output should be in Schematron Validation Report Language (SVRL). The output of this step may include PSVI annotations.

The p:validate-with-xml-schema step applies validity assessment to the source input. The values of the use-location-hints, try-namespaces, and assert-valid options must be boolean. The value of the mode option must be an NMTOKEN whose value is either “strict” or “lax”. Validation is performed against the set of schemas represented by the documents on the schema port. The use-location-hints and try-namespaces options allow the pipeline author to control how the schema processor should attempt to locate schema documents necessary but not provided on the schema port. Any schema documents provided on the schema port must be used in preference to schema documents located by other means. If the use-location-hints option is “true”, the processor should make use of schema location hints to locate schema documents. If the option is “false”, the processor should ignore any such hints. If the try-namespaces option is “true”, the processor should attempt to dereference the namespace URI to locate schema documents. If the option is “false”, the processor should not dereference namespace URIs. The mode option allow the pipeline author to control how schema validation begins. The “strict” mode means that the document element must be declared and schema-valid, otherwise it will be treated as invalid. The “lax” mode means that the absence of a declaration for the document element does not itself count as an unsuccessful outcome of validation. It is a dynamic error if the assert-valid option is true and the input document is not valid. When XML Schema validation assessment is performed, the processor is invoked in the mode specified by the mode option. It is a dynamic error if the implementation does not support the specified mode. The result of the assessment is a document with the Post-Schema-Validation-Infoset (PSVI) () annotations, if the pipeline implementation supports such annotations. If not, the input document is reproduced with any defaulting of attributes and elements performed as specified by the XML Schema recommendation.

The p:www-form-urldecode step decodes a x-www-form-urlencoded string into a set of parameters. The value option is interpreted as a string of parameter values encoded using the x-www-form-urlencoded algorithm. It turns each such encoded name/value pair into a parameter. The entire set of parameters is written (as a c:param-set) on the result output port. It is a dynamic error if the value provided is not a properly x-www-form-urlencoded value. If any parameter name occurs more than once in the encoded string, the resulting parameter set will contain a c:param for each instance. However, only one of these will actually be used if the parameter set is passed to another step on its parameter input port.

The p:www-form-urlencode step encodes a set of parameter values as a x-www-form-urlencoded string and injects it into the source document. The value of the match option must be an XSLTMatchPattern. The set of parameters is encoded as a single x-www-form-urlencoded string. The matched nodes are specified with the match pattern in the match option. For each matching node, the encoded string is used in the output. Nodes that do not match are copied without change. If the expression given in the match option matches an attribute, the encoded string is used as the new value of the attribute in the output. If the expression matches any other kind of node, the entire node (and not just its contents) is replaced by the encoded string.

The p:xquery step applies an query to the sequence of documents provided on the source port. If a sequence of documents is provided on the source port, the first document is assumed to be the initial context item. This sequence is also the default collection. The query port must receive a single document: If the document root element is c:query, the text descendants of this element are considered the query. Because XQuery is not necessarily well-formed XML, any markup that occurs in the query must be escaped. If the document root element is in the XQueryX namespace, the document is treated as an XQueryX-encoded query. Support for XQueryX is implementation-defined. If the document root element is c:data or has a c:content-type attribute that specifies a text content type or a media type that the implementation recognizes, then the text descendants of this element are considered the query. Otherwise, the interpretation of the query is implementation-defined. The result of the p:xquery step must be a sequence of documents. It is a dynamic error if the sequence that results from evaluating the XQuery contains items other than documents and elements. Any elements that appear in the result sequence will be treated as documents with the element as their document element. For example: declare namespace atom="http://www.w3.org/2005/Atom"; /atom:feed/atom:entry ]]> The output of this step may include PSVI annotations. The static context of the XQuery processor is augmented in the following way: Statically known default collection type document()* Statically known namespaces: The namespace declarations in-scope for the containing element or made available through p:namespaces. The dynamic context of the XQuery processor is augmented in the following way: Context item The first document that appears on the source port. Context position 1 Context size 1 Variable values Any parameters passed on the parameters port augment any implementation-defined variable bindings known to the XQuery processor. The parameter values are passed to the XQuery processor as values of type xs:untypedAtomic. Function implementations The function implementations provided by the XQuery processor. Current dateTime The point in time returned as the current dateTime is implementation-defined. Implicit timezone The implicit timezone is implementation-defined. Available documents The set of available documents (those that may be retrieved with a URI) is implementation-dependent. Available collections The set of available collections is implementation-dependent. Default collection The sequence of documents provided on the source port.

The following pipeline applies XInclude processing and schema validation before using XQuery: <p:pipeline xmlns:p="http://www.w3.org/ns/xproc"> <p:xinclude/> <p:validate-with-xml-schema name="validate"> <p:input port="schema"> <p:document href="http://example.com/path/to/schema.xsd"/> </p:input> </p:validate-with-xml-schema> <p:xquery> <p:input port="query"> <p:data href="countp.xq" /> </p:input> </p:xquery> </p:pipeline> Where countp.xq might contain: <count>{count(.//p)}</count>

The p:xsl-formatter step receives an document and renders the content. The result of rendering is stored to the URI provided via the href option. A reference to that result is produced on the output port. The value of the href option must be an anyURI. If it is relative, it is made absolute against the base URI of the element on which it is specified (p:with-option or p:xsl-formatter in the case of a syntactic shortcut value). The content-type of the output is controlled by the content-type option. This option specifies a media type as defined by . The option may include media type parameters as well (e.g. "application/someformat; charset=UTF-8"). The use of media type parameters on the content-type option is implementation-defined. If the content-type option is not specified, the output type is implementation-defined. The default should be PDF. A formatter may take any number of optional rendering parameters via the step's parameters; such parameters are defined by the XSL implementation used and are implementation-defined. The output of this step is a document containing a single c:result element whose content is the absolute URI of the document stored by the step.

Several steps in this step library require serialization options to control the serialization of XML. These options are used to control serialization as in the specification. The following options may be present on steps that perform serialization: byte-order-mark The value of this option must be a boolean. If it's not specified, the default varies by encoding: for UTF-16 it's true, for all others, it's false. cdata-section-elements The value of this option must be a list of QNames. They are interpreted as elements name. doctype-public The value of this option must be a string. The public identifier of the doctype. doctype-system The value of this option must be an anyURI. The system identifier of the doctype. It need not be absolute, and is not resolved. encoding A character set name. If no encoding is specified, the encoding used is implementation defined. If the method is “xml” or “xhtml”, the implementation defined encoding must be either UTF-8 or UTF-16. escape-uri-attributes The value of this option must be a boolean. include-content-type The value of this option must be a boolean. It is ignored unless the specified method is “xhtml” or “html”. indent The value of this option must be a boolean. media-type The value of this option must be a string. It specifies the media type (MIME content type). If not specified, the default varies according to the method: xml application/xml html text/html xhtml application/xhtml+xml text text/plain For methods other than xml, html, xhtml, and text; the media-type is implementation defined. method The value of this option must be a QName. It specifies the serialization method. normalization-form The value of this option must be an NMTOKEN, one of the enumerated values NFC, NFD, NFKC, NFKD, fully-normalized, none or an implementation-defined value. omit-xml-declaration The value of this option must be a boolean. standalone The value of this option must be an NMTOKEN, one of the enumerated values true, false, or omit. undeclare-prefixes The value of this option must be a boolean. version The value of this option must be a string. In order to be consistent with the rest of this specification, boolean values for the serialization parameters use “true” and “false” where the serialization specification uses “yes” and “no”. No change in semantics is implied by this different spelling. The method option controls the serialization method used by this component with standard values of 'html', 'xml', 'xhtml', and 'text' but only the 'xml' value is required to be supported. The interpretation of the remaining options is as specified in . Implementations may support other method values but their results are implementation-defined. It is a dynamic error if the requested method is not supported. A minimally conforming implementation must support the xml output method with the following option values: The version must support the value 1.0. The encoding must support the values UTF-8. The omit-xml-declaration must be supported. If the value is not specified or has the value no, an XML declaration must be produced. All other option values may be ignored for the xml output method. If a processor chooses to implement an option for serialization, it must conform to the semantics defined in the specification. The use-character-maps parameter in specification has not been provided in the standard serialization options provided by this specification.

Conformant processors must implement all of the features described in this specification except those that are explicitly identified as optional. Some aspects of processor behavior are not completely specified; those features are either implementation-dependent or implementation-defined. An implementation-dependent feature is one where the implementation has discretion in how it is performed. Implementations are not required to document or explain how implementation-dependent features are performed. An implementation-defined feature is one where the implementation has discretion in how it is performed. Conformant implementations must document how implementation-defined features are performed.

The following features are implementation-defined:

The following features are implementation-dependent:

This specification conforms to the XML Information Set . The information corresponding to the following information items and properties must be available to the processor for the documents that flow through the pipeline. The Document Information Item with base URI and children properties. Element Information Items with base URI, children, attributes, in-scope namespaces, prefix, local name, namespace name, parent properties. Attribute Information Items with namespace name, prefix, local name, normalized value, attribute type, and owner element properties. Character Information Items with character code, parent, and, optionally, element content whitespace properties. Processing Instruction Information Items with base URI, target, content and parent properties. Comment Information Items with content and parent properties. Namespace Information Items with prefix and namespace name properties. It is implementation-defined whether additional information items and properties, particularly those made available in the PSVI, are preserved between steps.

Use Cases XML Processing Model Requirements and Use Cases. Alex Milowski, editor. W3C Working Draft 11 April 2006. Infoset XML Information Set (Second Edition). John Cowan, Richard Tobin, editors. W3C Working Group Note 04 February 2004. XML 1.0 Extensible Markup Language (XML) 1.0 (Fourth Edition). Tim Bray, Jean Paoli, C. M. Sperberg-McQueen, et. al. editors. W3C Recommendation 16 August 2006. Namespaces 1.0 Namespaces in XML 1.0 (Second Edition). Tim Bray, Dave Hollander, Andrew Layman, et. al., editors. W3C Recommendation 16 August 2006. XML 1.1 Extensible Markup Language (XML) 1.1 (Second Edition). Tim Bray, Jean Paoli, C. M. Sperberg-McQueen, et. al. editors. W3C Recommendation 16 August 2006. Namespaces 1.1 Namespaces in XML 1.1 (Second Edition). Tim Bray, Dave Hollander, Andrew Layman, et. al., editors. W3C Recommendation 16 August 2006. XPath 1.0 XML Path Language (XPath) Version 1.0. James Clark and Steve DeRose, editors. W3C Recommendation. 16 November 1999. XSLT 1.0 XSL Transformations (XSLT) Version 1.0. James Clark, editor. W3C Recommendation. 16 November 1999. XPath 2.0 XML Path Language (XPath) 2.0. Anders Berglund, Scott Boag, Don Chamberlin, et. al., editors. W3C Recommendation. 23 January 2007. XQuery 1.0 and XPath 2.0 Data Model (XDM) XQuery 1.0 and XPath 2.0 Data Model (XDM). Mary Fernández, Ashok Malhotra, Jonathan Marsh, et. al., editors. W3C Recommendation. 23 January 2007. XPath 2.0 Functions and Operators XQuery 1.0 and XPath 2.0 Functions and Operators. Ashok Malhotra, Jim Melton, and Norman Walsh, editors. W3C Recommendation. 23 January 2007. XSLT 2.0 XSL Transformations (XSLT) Version 2.0. Michael Kay, editor. W3C Recommendation. 23 January 2007. XSL 1.1 Extensible Stylesheet Language (XSL) Version 1.1. Anders Berglund, editor. W3C Recommendation. 5 December 2006. XQuery 1.0 XQuery 1.0: An XML Query Language. Scott Boag, Don Chamberlin, Mary Fernández, et. al., editors. W3C Recommendation. 23 January 2007. RELAX NGISO/IEC JTC 1/SC 34. ISO/IEC 19757-2:2003(E) Document Schema Definition Languages (DSDL) — Part 2: Grammar-based validation — RELAX NG 2003. RELAX NG Compact SyntaxISO/IEC JTC 1/SC 34. ISO/IEC 19757-2:2003/Amd 1:2006 Document Schema Definition Languages (DSDL) — Part 2: Grammar-based validation — RELAX NG AMENDMENT 1 Compact Syntax 2006. RELAX NG DTD Compatibility RELAX NG DTD Compatibility. OASIS Committee Specification. 3 December 2001. SchematronISO/IEC JTC 1/SC 34. ISO/IEC 19757-3:2006(E) Document Schema Definition Languages (DSDL) — Part 3: Rule-based validation — Schematron 2006. W3C XML Schema: Part 1 XML Schema Part 1: Structures Second Edition. Henry S. Thompson, David Beech, Murray Maloney, et. al., editors. World Wide Web Consortium, 28 October 2004. W3C XML Schema: Part 2 XML Schema Part 2: Datatypes Second Edition. Paul V. Biron and Ashok Malhotra, editors. World Wide Web Consortium, 28 October 2004. xml:id xml:id Version 1.0. Jonathan Marsh, Daniel Veillard, and Norman Walsh, editors. W3C Recommendation. 9 September 2005. XInclude XML Inclusions (XInclude) Version 1.0 (Second Edition). Jonathan Marsh, David Orchard, and Daniel Veillard, editors. W3C Recommendation. 15 November 2005. XML Base XML Base. Jonathan Marsh, editor. W3C Recommendation. 27 June 2001. XPointer Framework XPointer Framework. Paul Grosso, Eve Maler, Jonathan Marsh, et. al., editors. W3C Recommendation. 25 March 2003. XPointer element() Scheme XPointer element() Scheme. Paul Grosso, Eve Maler, Jonathan Marsh, et. al., editors. W3C Recommendation. 25 March 2003. Serialization XSLT 2.0 and XQuery 1.0 Serialization. Scott Boag, Michael Kay, Joanne Tong, Norman Walsh, and Henry Zongaro, editors. W3C Recommendation. 23 January 2007. MD5 RFC 1321: The MD5 Message-Digest Algorithm. R. Rivest. Network Working Group, IETF, April 1992. RFC 1521 RFC 1521: MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies. N. Borenstein, N. Freed, editors. Internet Engineering Task Force. September, 1993. RFC 2119 Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. Network Working Group, IETF, Mar 1997. RFC 2616 RFC 2616: Hypertext Transfer Protocol — HTTP/1.1. R. Fielding, J. Gettys, J. Mogul, et. al., editors. Internet Engineering Task Force. June, 1999. RFC 2617 RFC 2617: HTTP Authentication: Basic and Digest Access Authentication. J. Franks, P. Hallam-Baker, J. Hostetler, S. Lawrence, P. Leach, A. Luotonen, L. Stewart. June, 1999 . RFC 3023 RFC 3023: XML Media Types. M. Murata, S. St. Laurent, and D. Kohn, editors. Internet Engineering Task Force. January, 2001. RFC 3548 RFC 3548: The Base16, Base32, and Base64 Data Encodings. S. Josefsson, Editor. Internet Engineering Task Force. July, 2003. RFC 3986 RFC 3986: Uniform Resource Identifier (URI): General Syntax. T. Berners-Lee, R. Fielding, and L. Masinter, editors. Internet Engineering Task Force. January, 2005. RFC 3987 RFC 3987: Internationalized Resource Identifiers (IRIs). M. Duerst and M. Suignard, editors. Internet Engineering Task Force. January, 2005. Unicode TR#17 Unicode Technical Report #17: Character Encoding Model. Ken Whistler, Mark Davis, and Asmus Freytag, authors. The Unicode Consortium. September, 2004. IANA Media Types IANA MIME Media Types. Internet Engineering Task Force. HTML Tidy HTML Tidy Library Project. SourceForge project. TagSoup TagSoup - Just Keep On Truckin'. John Cowan. UUID ITU X.667: Information technology - Open Systems Interconnection - Procedures for the operation of OSI Registration Authorities: Generation and registration of Universally Unique Identifiers (UUIDs) and their use as ASN.1 Object Identifier components. 2004. SHA1 Federal Information Processing Standards Publication 180-1: Secure Hash Standard. 1995.

RFC 4122 RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace. P. Leach and M. Mealling, editors. Internet Engineering Task Force. July, 2005. CRC32 “32-Bit Cyclic Redundancy Codes for Internet Applications”, The International Conference on Dependable Systems and Networks: 459. 10.1109/DSN.2002.1028931. P. Koopman. June 2002.

Namespaces in XMLUnless otherwise noted, the term Namespaces in XML refers equally to and .XMLXProc is intended to work equally well with and . Unless otherwise noted, the term “XML” refers equally to both versions.ancestorsThe ancestors of a step, if it has any, are its container and the ancestors of its container.atomic stepAn atomic step is a step that performs a unit of XML processing, such as XInclude or transformation, and has no internal subpipeline. bindingA binding associates an input or output port with some data source.by URIA document is specified by URI if it is referenced with a URI.by sourceA document is specified by source if it references a specific port on another step.compound stepA compound step is a step that contains a subpipeline.contained stepsThe steps that occur directly within, or within non-step wrappers directly within, a step are called that step's contained steps. In other words, “container” and “contained steps” are inverse relationships.containerA compound step or multi-container step is a container for the steps directly within it or within non-step wrappers directly within it.declared inputsThe input ports declared on a step are its declared inputs.declared optionsThe options declared on a step are its declared options.declared outputsThe output ports declared on a step are its declared outputs.default readable portThe default readable port, which may be undefined, is a specific step name/port name pair from the set of readable ports.dynamic errorA dynamic error is one which occurs while a pipeline is being evaluated.empty environmentThe empty environment contains no readable ports, an undefined default readable port and no in-scope bindings.empty sequenceAn empty sequence of documents is specified with the p:empty element.environmentThe environment is a context-dependent collection of information available within sub-pipelines.extension attributeAn element from the XProc namespace may have any attribute not from the XProc namespace, provided that the expanded-QName of the attribute has a non-null namespace URI. Such an attribute is called an extension attribute.in-scope bindingsThe in-scope bindings are a set of name-value pairs, based on option and variable bindings.inherited environmentThe inherited environment of a contained step is an environment that is the same as the environment of its container with the standard modifications. inline documentAn inline document is specified directly in the body of the element that binds it.last stepThe last step in a subpipeline is its last step in document order.matchesA step matches its signature if and only if it specifies an input for each declared input, it specifies no inputs that are not declared, it specifies an option for each option that is declared to be required, and it specifies no options that are not declared.multi-container stepA multi-container step is a step that contains several alternate subpipelines. namespace fixupTo produce a serializable XML document, the XProc processor must sometimes add additional namespace nodes, perhaps even renaming prefixes, to satisfy the constraints of Namespaces in XML. This process is referred to as namespace fixup.optionAn option is a name/value pair where the name is an expanded name and the value must be a string or xs:untypedAtomic.parameterA parameter is a name/value pair where the name is an expanded name and the value must be a string or xs:untypedAtomic.parameter input portA parameter input port is a distinguished kind of input port which accepts (only) dynamically constructed parameter name/value pairs.pipelineA pipeline is a set of connected steps, with outputs of one step flowing into inputs of another.primary input portIf a step has a document input port which is explicitly marked “primary='true'”, or if it has exactly one document input port and that port is not explicitly marked “primary='false'”, then that input port is the primary input port of the step.primary output portIf a step has a document output port which is explicitly marked “primary='true'”, or if it has exactly one document output port and that port is not explicitly marked “primary='false'”, then that output port is the primary output port of the step.primary parameter input portIf a step has a parameter input port which is explicitly marked “primary='true'”, or if it has exactly one parameter input port and that port is not explicitly marked “primary='false'”, then that parameter input port is the primary parameter input port of the step.readable portsThe readable ports are a set of step name/port name pairs.signatureThe signature of a step is the set of inputs, outputs, and options that it is declared to accept.specified optionsThe options on a step which have specified values, either because a p:with-option element specifies a value or because the declaration included a default value, are its specified options.static errorA static error is one which can be detected before pipeline evaluation is even attempted.stepA step is the basic computational unit of a pipeline.subpipelineSibling steps (and the connections between them) form a subpipeline.variableA variable is a name/value pair where the name is an expanded name and the value must be a string or xs:untypedAtomic.visibleIf two names are in the same scope, we say that they are visible to each other. This appendix summarizes the XProc pipeline language. Machine readable descriptions of this language are available in RELAX NG (and the RELAX NG compact syntax), W3C XML Schema, and DTD syntaxes. The core steps are also summarized here. As are the optional steps. And the step vocabulary elements. The following error codes are defined by this specification.

The following static errors are defined:

The following dynamic errors are defined:

The following dynamic errors can be raised by steps in this specification:

An XProc processor may find it necessary to add missing namespace declarations to ensure that a document can be serialized. While this process is implementation defined, the purpose of this appendix is to provide guidance as to what an implementation might do to either prevent such situations or fix them as before serialization. When a namespace binding is generated, the prefix associated with the QName of the element or attribute in question should be used. From an Infoset perspective, this is accomplished by setting the [prefix] on the element or attribute. Then when an implementation needs to add a namespace binding, it can reuse that prefix if possible. If reusing the prefix is not possible, the implementation must generate a new prefix that is unique to the in-scope namespace of the element or owner element of the attribute. An implementation can avoid namespace fixup by making sure that the standard step library does not output documents that require fixup. The following list contains suggestions as to how to accomplish this within the steps: Any step that outputs an element in the step vocabulary namespace http://www.w3.org/ns/xproc-step must ensure that namespace is declared. An implementation should generate a namespace binding using the prefix “c”. When attributes are added by p:add-attribute or p:set-attributes, the step must ensure the namespace of the attributes added are declared. If the prefix used by the QName is not in the in-scope namespaces of the element on which the attribute was added, the step must add a namespace declaration of the prefix to the in-scope namespaces. If the prefix is amongst the in-scope namespace and is not bound to the same namespace name, a new prefix and namespace binding must be added. When a new prefix is generated, the prefix associated with the attribute should be changed to reflect that generated prefix value. When an element is renamed by p:rename, the step must ensure the namespace of the element is declared. If the prefix used by the QName is not in the in-scope namespaces of the element being renamed, the step must add a namespace declaration of the prefix to the in-scope namespaces. If the prefix is amongst the in-scope namespace and is not bound to the same namespace name, a new prefix and namespace binding must be added. When a new prefix is generated, the prefix associated with the element should be changed to reflect that generated prefix value. If the element does not have a namespace name and there is a default namespace, the default namespace must be undeclared. For each of the child elements, the original default namespace declaration must be preserved by adding a default namespace declaration unless the child element has a different default namespace. When an attribute is renamed by p:rename, the step must ensure the namespace of the renamed attribute is declared. If the prefix used by the QName is not in the in-scope namespaces of the element on which the attribute was added, the step must add a namespace declaration of the prefix to the in-scope namespaces. If the prefix is amongst the in-scope namespace and is not bound to the same namespace name, a new prefix and namespace binding must be added. When a new prefix is generated, the prefix associated with the attribute should be changed to reflect that generated prefix value. When an element wraps content via p:wrap, there may be in-scope namespaces coming from ancestor elements of the new wrapper element. The step must ensure the namespace of the element is declared properly. By default, the wrapper element will inherit the in-scope namespaces of the parent element if one exists. As such, there may be a existing namespace declaration or default namespace. If the prefix used by the QName is not in the in-scope namespaces of the wrapper element, the step must add a namespace declaration of the prefix to the in-scope namespaces. If the prefix is amongst the in-scope namespace and is not bound to the same namespace name, a new prefix and namespace binding must be added. When a new prefix is generated, the prefix associated with the wrapper element should be changed to reflect that generated prefix value. If the element does not have a namespace name and there is a default namespace, the default namespace must be undeclared. For each of the child elements, the original default namespace declaration must be preserved by adding a default namespace declaration unless the child element has a different default namespace. When the wrapper element is added for p:wrap-sequence or p:pack, the prefix used by the QName must be added to the in-scope namespaces. When a element is removed via p:unwrap, an in-scope namespaces that are declared on the element must be copied to any child element except when the child element declares the same prefix or declares a new default namespace. In the output from p:xslt, if an element was generated from the xsl:element or an attribute from xsl:attribute, the step must guarantee that an namespace declaration exists for the namespace name used. Depending on the XSLT implementation, the namespace declaration for the namespace name of the element or attribute may not be declared. It may also be the case that the original prefix is available. If the original prefix is available, the step should attempt to re-use that prefix. Otherwise, it must generate a prefix for a namespace binding and change the prefix associated the element or attribute. When handling imports, an implementation should be able to detect the following situations: Circular imports: A imports B, B imports A. Re-entrant imports: A imports B and C, B imports D, C imports D. To accomplish this, an implementation can use the following strategy: For a pipeline or library, process all the p:import elements and record the URI of each resource returned. If the same resource URI is encountered more than once, do not load and process that resource after the first time. For each resource, determine the exported step types defined by the resource that are defined within the resource and not by an import by the following rules: The pipeline name if the resource is a pipeline. Any p:declare-step element within a library. Associated with every resource URI a list of step types declared within and a list of the "top level" imported resource URI values (i.e. the base URI of the resolved resource for each p:import element in the library or pipeline). This is effectively two maps: D: {uri} -> {set of step declarations} I: {uri} -> {set of uris} For any resource, the set of new types is: N: ({uri}, {set of uris}} -> ({set of step declarations},{set of uris}) N(U,P) := let R := D(U) for each k in I(U) if k not in P P:= union of { P, k } let r:= N(k,P) R:= union of (R,r[0]) P:= r[1] return (R,P) If N(U,P) contains duplicates, then the same step name is declared in different resources (which is an error). For any resource, the set of types is: S: {uri} -> {set of step declarations} S(U) := N(U,{})[0] If S(U) contains any duplicates, then the same step name is declared in different resources (which is an error). An implementation can use the maps N and S as necessary to resolve imports. XProc imposes as few constraints on the order in which steps must be evaluated as possible and almost no constraints on parallel execution. In the simple, and we believe overwhelmingly common case, inputs flow into the pipeline, through the pipeline from one step to the next, and results are produced at the end. The order of the steps is constrained by the input/output connections between them. Implementations are free to execute them in a purely sequential fashion or in parallel, as they see fit. The results are the same in either case. This is not true for pipelines which rely on side effects, such as the state of the filesystem or the state of the web. Consider the following pipeline: <p:pipeline xmlns:p="http://www.w3.org/ns/xproc" name="main"> <p:xslt name="generate-stylesheet"> <p:input port="source"> <p:document href="someURI"/> </p:input> <p:input port="stylesheet"> <p:document href="someOtherURI"/> </p:input> </p:xslt> <p:store name="save-xslt" href="gen-style.xsl"/> <p:xslt name="style"> <p:input port="source"> <p:pipe step="main" port="source"/> </p:input> <p:input port="stylesheet"> <p:document href="gen-style.xsl"/> </p:input> </p:xslt> </p:pipeline> There's no guarantee that “style” step will execute after the “save-xslt” step. In this case, the solution is straightforward. Even if you need the saved stylesheet, you don't need to rely on it in your pipeline: <p:pipeline xmlns:p="http://www.w3.org/ns/xproc" name="main"> <p:xslt name="generate-stylesheet"> <p:input port="source"> <p:document href="someURI"/> </p:input> <p:input port="stylesheet"> <p:document href="someOtherURI"/> </p:input> </p:xslt> <p:store name="save-xslt" href="gen-style.xsl"/> <p:xslt name="style"> <p:input port="source"> <p:pipe step="main" port="source"/> </p:input> <p:input port="stylesheet"> <p:pipe step="generate-stylesheet" port="result"/> </p:input> </p:xslt> </p:pipeline> Now the result is independent of the implementation strategy. Implementations are free to invent additional control structures using p:pipeinfo and extension attributes to provide greater control over parallelism in their implementations.