xsl:copy-of

Description

xsl:copy-of evaluates the select expression and copies the entire result into the output tree. Unlike xsl:copy, which copies only the current node shallowly, xsl:copy-of performs a deep copy: element nodes are copied with all their attributes, namespace nodes, and all descendant nodes recursively.

If the select expression yields a node-set, each node in the set is deep-copied in document order. If the expression yields a string, number, or boolean, it is converted to its string representation and output as a text node — which is the same behaviour as xsl:value-of.

A particularly important use in XSLT 1.0 is copying result tree fragments stored in variables. A content-based xsl:variable produces an RTF, and xsl:copy-of is one of the few operations that can emit an RTF into the result tree directly without first converting it to a string.

Attributes

Examples

Deep copy of a subtree

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<catalog>
  <product id="p1">
    <name>Widget</name>
    <specs>
      <weight unit="kg">0.5</weight>
      <color>blue</color>
    </specs>
  </product>
  <product id="p2">
    <name>Gadget</name>
    <specs>
      <weight unit="kg">1.2</weight>
      <color>red</color>
    </specs>
  </product>
</catalog>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/catalog">
    <selected>
      <xsl:copy-of select="product[@id='p1']"/>
    </selected>
  </xsl:template>
</xsl:stylesheet>

Output:

<selected>
  <product id="p1">
    <name>Widget</name>
    <specs>
      <weight unit="kg">0.5</weight>
      <color>blue</color>
    </specs>
  </product>
</selected>

Copying a result tree fragment from a variable

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<data><value>42</value></data>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/data">
    <xsl:variable name="box">
      <wrapper>
        <content><xsl:value-of select="value"/></content>
      </wrapper>
    </xsl:variable>
    <root>
      <xsl:copy-of select="$box"/>
      <xsl:copy-of select="$box"/>
    </root>
  </xsl:template>
</xsl:stylesheet>

Output:

<root>
  <wrapper><content>42</content></wrapper>
  <wrapper><content>42</content></wrapper>
</root>

Notes

• xsl:copy-of preserves namespace nodes of copied elements. If namespaces from the source document are not desired in the output, you will need to rebuild the elements manually or use exclude-result-prefixes on the stylesheet element.
• Unlike xsl:value-of, xsl:copy-of does not serialize the node to text — it inserts actual node copies, preserving XML structure.
• When the select expression is a string or number, xsl:copy-of and xsl:value-of produce identical results. The meaningful difference arises with node-sets and RTFs.
• In XSLT 2.0+, xsl:copy-of accepts a copy-namespaces attribute (yes / no) to control whether namespace nodes are included in element copies.

See also

• xsl:copy
• xsl:variable