# fn:idref - XPath XQuery Reference

Returns the sequence of element or attribute nodes with an IDREF value
            matching the value of one or more of the ID values supplied in
               $arg.deterministiccontext-dependentfocus-dependentdeterministiccontext-independentfocus-independent The function returns a sequence, in document order with duplicates eliminated,
            containing every element or attribute node $N that satisfies all the
            following conditions:$N is in the target document. The target document is the document
                  containing $node or the document containing the context item
                     (.) if the second argument is omitted. The behavior of the
                  function if $node is omitted is exactly the same as if the context
                  item had been passed as $node.$N has an IDREF value equal to one of the candidate
                     ID values, where:A node $N has an IDREF value equal to
                           V if both of the following conditions are true:The is-idrefs property (see ) of $N is true.The sequence 
									fn:tokenize(fn:normalize-space(fn:string($N)), ' ')contains a string that is
                              equal to V under the rules of the eq
                              operator using the Unicode code point collation
                                 (http://www.w3.org/2005/xpath-functions/collation/codepoint).Each xs:string in $arg is parsed as if it were of
                        lexically of type xs:ID. These xs:strings are then
                        included in the list of candidate xs:IDs. If any of the strings
                        in $arg is not a lexically valid xs:ID (that is,
                        if it is not lexically an xs:NCName), it is ignored. More
                        formally, the candidate ID values are the strings in the
                        sequence:$arg[. castable as xs:NCName]
      validate lax {  
        document {    
          <employees xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
                     xmlns:xs="http://www.w3.org/2001/XMLSchema">  
            <employee xml:id="ID21256">
               <empnr xsi:type="xs:ID">E21256</empnr>
               <first>Anil</first>
               <last>Singh</last>
               <deputy xsi:type="xs:IDREF">E30561</deputy>
            </employee>
            <employee xml:id="ID30561">
               <empnr xsi:type="xs:ID">E30561</empnr>
               <first>John</first>
               <last>Brown</last>
               <manager xsi:type="xs:IDREF">ID21256</manager>
            </employee>
          </employees>
        }
      }$emp/(element-with-id('ID21256')/@xml:id => fn:idref())/ancestor::employee/last => string()"Brown"Assuming that manager has the is-idref property, the call on fn:idref selects
                  the manager element. If, instead, the manager had a ref
               attribute with the is-idref property, the call on fn:idref would select the attribute node.$emp/(element-with-id('E30561')/empnr => fn:idref())/ancestor::employee/last => string()"Singh"Assuming that employee/deputy has the is-idref property, the call on fn:idref selects
                  the deputy element.A dynamic error is raised  if
               $node, or the context item if the second argument is omitted, is a node
            in a tree whose root is not a document node. The following errors may be raised when $node is omitted:If the context item is absent,
                  dynamic error If the context item is not a node, type error . An element or attribute typically acquires the is-idrefs property by being
            validated against the schema type xs:IDREF or xs:IDREFS, or
            (for attributes only) by being described as of type IDREF or
               IDREFS in a DTD.Because the function is sensitive to the way in which the data model
         is constructed, calls on this function are not always interoperable. No error is raised in respect of a candidate ID value that does not match
            the IDREF value of any element or attribute in the document. If no
            candidate ID value matches the IDREF value of any element or
            attribute, the function returns the empty sequence. It is possible for two or more nodes to have an IDREF value that matches a
            given candidate ID value. In this situation, the function will return all
            such nodes. However, each matching node will be returned at most once, regardless how
            many candidate ID values it matches. It is possible in a well-formed but invalid document to have a node whose
               is-idrefs property is true but that does not conform to the lexical
            rules for the xs:IDREF type. The effect of the above rules is that
            ill-formed candidate ID values and ill-formed IDREF values are
            ignored.If the data model is constructed from a PSVI, the typed value of a node that has the
               is-idrefs property will contain at least one atomic value of type
               xs:IDREF (or a type derived by restriction from xs:IDREF).
            It may also contain atomic values of other types. These atomic values are treated as
            candidate ID values if two conditions are met: their lexical form must be valid as an
               xs:NCName, and there must be at least one instance of xs:IDREF
            in the typed value of the node. If these conditions are not satisfied, such values are ignored.