xsl:processing-instruction

Description

xsl:processing-instruction inserts a processing instruction (PI) node into the result tree. A processing instruction has the form <?target data?>, where target is the PI name and data is the optional text body.

Processing instructions are used to embed application-specific directives inside XML documents. Common examples include <?xml-stylesheet?> for attaching stylesheets, <?php ... ?> for PHP code, and <?xml-model?> for schema association. In XSLT transformations, they are typically used to produce these directives programmatically based on source data.

The name attribute is an attribute value template, so the PI target name can be computed. The content of xsl:processing-instruction produces the data portion of the PI as a string; it may include xsl:value-of, xsl:text, and variables.

Attributes

Examples

Adding an xml-stylesheet PI

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<docs>
  <doc theme="dark">Manual</doc>
  <doc theme="light">Guide</doc>
</docs>

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="/docs">
    <xsl:apply-templates select="doc"/>
  </xsl:template>

  <xsl:template match="doc">
    <xsl:processing-instruction name="xml-stylesheet">
      <xsl:text>href="</xsl:text>
      <xsl:value-of select="@theme"/>
      <xsl:text>.css" type="text/css"</xsl:text>
    </xsl:processing-instruction>
    <document><xsl:value-of select="."/></document>
  </xsl:template>
</xsl:stylesheet>

Output:

<?xml-stylesheet href="dark.css" type="text/css"?>
<document>Manual</document>
<?xml-stylesheet href="light.css" type="text/css"?>
<document>Guide</document>

Computed PI name from source data

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<config>
  <directive app="php">echo "hello";</directive>
</config>

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="/config">
    <output>
      <xsl:for-each select="directive">
        <xsl:processing-instruction name="{@app}">
          <xsl:value-of select="."/>
        </xsl:processing-instruction>
      </xsl:for-each>
    </output>
  </xsl:template>
</xsl:stylesheet>

Output:

<output>
  <?php echo "hello";?>
</output>

Notes

• The PI name must not be xml or XML in any capitalisation — this is reserved by the XML specification. Processors must reject it with an error.
• The data portion of the PI must not contain ?>, as that would prematurely end the PI. If generated content might include this sequence, guard against it or transform the input.
• When the output method is text, processing instructions are silently omitted.
• PIs are not visible in rendered HTML, but they appear in the raw source and are accessible via the DOM in browsers.

See also

• xsl:comment
• xsl:output
• xsl:text