id Function

Selects elements by their unique ID.

node-set id(object)

Remarks

When the argument is of type node-set, the result is the union of the result of applying id() to the string value of each of the nodes in the node-set argument.

When the argument is of any other type, it is converted to a string and then split into a white space–separated list of tokens (white space is any sequence of characters matching the production); the result is a node-set containing the elements in the same document as the context node that have a unique ID equal to any of the tokens in the list.

Example

XML FILE (test.xml)

<?xml version="1.0"?>
<!DOCTYPE test [
  <!ELEMENT test (x+)>
  <!ELEMENT x (x+, y+)>
  <!ATTLIST x
     a ID #REQUIRED>
  <!ELEMENT y ANY>
]>
<test>
    <x a="a11">
      <x a="a21">
        <x a="a31">
          <y>y31</y>
          <y>y32</y>
        </x>
      </x>
    </x>
    <x a="a12">
      <x a="a22">
        <y>y21</y>
        <y>y22</y>
      </x>
    </x>
    <x a="13">
      <y>y11</y>
      <y>y12</y>
    </x>
    <x a="a14">
      <y>y03</y>
      <y>y04</y>
    </x>
</test>

XSLT File (test.xsl)

<?xml version='1.0'?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:output method="xml" omit-xml-declaration="yes"/>

  <!-- suppress text nodes not covered in subsequent        template rule -->
  <xsl:template match="text()"/>

  <xsl:template match="*">
    <xsl:element name="{name()}">
      <xsl:apply-templates select="*|@*"/>
      <xsl:if test="text()">
         <xsl:value-of select="."/>
      </xsl:if>
    </xsl:element>
  </xsl:template>

  <xsl:template match="@*">
    <xsl:attribute name="{name()}">
      <xsl:value-of select="."/>
    </xsl:attribute>
  </xsl:template>

  <xsl:template match="/test">
    <xsl:apply-templates select="id('a21') "/>
and 
    <xsl:apply-templates select="id('a11')//y[1]"/>
  </xsl:template>

</xsl:stylesheet>

Output

The XSLT stylesheet, when applied to the XML file above results in the following node-set:

   <x a="a21">
      <x a="a31">
         <y>y31</y>
         <y>y32</y>
      </x>
   </x>
and
   <y>y31</y>

See Also

Data Types in Schemas | XDR Schema Data Types Reference | XML Data Types Reference