container of set of alternative content. container of one -- alternative--. container of one -- alternative--. container of -- optional content --. definition of a variable. include the value into the content. container of processing options. Name of the attribute that will be assigned the value of selid. Processing options. Specify required XPath functions. XPath expression which resolves to a boolean to control inclusion of optional content. Will become the ID after processing. Name of the attribute that will be assigned the value of selid.