Returns the sequence of element nodes that have an ID value matching the
value of one or more of the IDREF values supplied in $arg.
fn:id( $arg as xs:string*element()*fn:id( $arg as xs:string*,$node as node()element()*The function returns a sequence, in document order with duplicates eliminated,
containing every element node E that satisfies all the following
conditions:
E 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.
E has an ID value equal to one of the candidate
IDREF values, where:
An element has an ID value equal to V if either
or both of the following conditions are true:
The is-id property (See .) of the element node is true, and the typed value
of the element node is equal to V under the rules of the
eq operator using the Unicode codepoint collation
(http://www.w3.org/2005/xpath-functions/collation/codepoint).
The element has an attribute node whose is-id property
(See .) is true and whose typed
value 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
type IDREFS, that is, each xs:string in
$arg is treated as a whitespace-separated sequence of
tokens, each acting as an IDREF. These tokens are then included
in the list of candidate IDREFs. If any of the tokens is not a
lexically valid IDREF (that is, if it is not lexically an
xs:NCName), it is ignored. Formally, the candidate
IDREF values are the strings in the sequence given by the
expression:
If several elements have the same ID value, then E is
the one that is first in document order.
let $emp :=
The expression $emp/id('ID21256')/name() returns "employee".
The expression $emp/id('E21256')/name() returns "empnr".
A dynamic error is raised if
$node, or the context item if the second argument is absent, 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 .
The effect of this function is anomalous in respect of element nodes with the
is-id property. For legacy reasons, this function returns the element
that has the is-id property, whereas it would be more appropriate to return
its parent, that being the element that is uniquely identified by the ID. A new function
fn:element-with-id has been introduced with the desired
behavior.
If the data model is constructed from an Infoset, an attribute will have the
is-id property if the corresponding attribute in the Infoset had an
attribute type of ID: typically this means the attribute was declared as an
ID in a DTD.
If the data model is constructed from a PSVI, an element or attribute will have the
is-id property if its typed value is a single atomic value of type
xs:ID or a type derived by restriction from xs:ID.
No error is raised in respect of a candidate IDREF value that does not
match the ID of any element in the document. If no candidate
IDREF value matches the ID value of any element, the
function returns the empty sequence.
It is not necessary that the supplied argument should have type xs:IDREF
or xs:IDREFS, or that it should be derived from a node with the
is-idrefs property.
An element may have more than one ID value. This can occur with synthetic
data models or with data models constructed from a PSVI where the element and one of its
attributes are both typed as xs:ID.
If the source document is well-formed but not valid, it is possible for two or more
elements to have the same ID value. In this situation, the function will
select the first such element.
It is also possible in a well-formed but invalid document to have an element or
attribute that has the is-id property but whose value does not conform to
the lexical rules for the xs:ID type. Such a node will never be selected by
this function.