XSLT Reference

xsl:message

XSLT 1.0 element

Emits a diagnostic message to the processor's error output; optionally terminates transformation with terminate='yes'.

Syntax

<xsl:message terminate="no|yes">message content</xsl:message>

Description

xsl:message sends a diagnostic message to the XSLT processor’s message destination, which is typically standard error or a log. The content of the element is a sequence constructor: any combination of literal text, value-of, elements, or other instructions that would be legal inside a template. The resulting nodes form the message.

When terminate="yes", the processor stops the transformation immediately after emitting the message and reports an error. This is useful for asserting preconditions at the start of a transformation or validating input data before processing begins.

The exact format and destination of messages is implementation-defined. Saxon writes them to standard error; other processors may write to a log file or fire a callback.

Parameters

Parameter	Type	Required	Description
`terminate`	`yes` or `no`	No	When `yes`, the processor stops the transformation after emitting the message (default `no`).
`select`	expression	No	XPath 2.0+ alternative to element content for specifying the message.
`error-code`	QName	No	XSLT 3.0. An error code attached to the message when `terminate="yes"`.

Return value

xsl:message produces no nodes in the result tree.

Examples

Validation guard with terminate

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<order>
  <item quantity="-3">Widget</item>
</order>

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="/order">
    <xsl:if test="item/@quantity &lt; 0">
      <xsl:message terminate="yes">
        ERROR: Negative quantity found for item: <xsl:value-of select="item"/>
      </xsl:message>
    </xsl:if>
    <processed><xsl:copy-of select="."/></processed>
  </xsl:template>
</xsl:stylesheet>

Output (message sent to error output, transformation aborted):

ERROR: Negative quantity found for item: Widget

Logging progress without termination

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<records>
  <record id="1">Alpha</record>
  <record id="2">Beta</record>
  <record id="3">Gamma</record>
</records>

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="/records">
    <output>
      <xsl:for-each select="record">
        <xsl:message>Processing record id=<xsl:value-of select="@id"/></xsl:message>
        <item><xsl:value-of select="."/></item>
      </xsl:for-each>
    </output>
  </xsl:template>
</xsl:stylesheet>

Result tree:

<output>
  <item>Alpha</item>
  <item>Beta</item>
  <item>Gamma</item>
</output>

Messages Processing record id=1, Processing record id=2, and Processing record id=3 are sent to error output.

Notes

The message destination is processor-dependent and cannot be configured from within the stylesheet in XSLT 1.0. Use processor-specific APIs or command-line flags to redirect messages.
In XSLT 2.0 and later, xsl:message can use the select attribute as an alternative to element content.
In XSLT 3.0, terminate="yes" combined with error-code allows catching the error with try/catch in the calling stylesheet.
Avoid leaving terminate="no" messages in production stylesheets without purpose; they slow down transformation and pollute logs.