XSLT Reference

xsl:map-entry

XSLT 3.0 element

Adds a single key-value pair to an xsl:map, where the key is any atomic value and the value is any XDM sequence.

Syntax

<xsl:map-entry key="expression" select="expression"/>

Description

xsl:map-entry contributes a single key-value pair to the enclosing xsl:map. The key attribute is an XPath expression that must evaluate to a single atomic value — strings, integers, dates, and QNames are all valid key types. The value is provided either via the select attribute or via a sequence constructor in the element content.

Because xsl:map-entry is an XSLT instruction, you can use it inside xsl:for-each to programmatically add entries, or inside xsl:if/xsl:choose to conditionally include entries. This makes xsl:map-entry more flexible than the XPath map{...} constructor syntax when the data is dynamic.

Keys within a single map must be distinct. Two atomic values are equal as map keys if they are equal according to the eq operator with the same implicit timezone. If the same key appears twice in the xsl:map, the processor raises error XTDE3365.

The value can be any XDM sequence including the empty sequence, nodes, arrays, and even nested maps, making xsl:map-entry the building block for arbitrarily nested data structures.

Attributes

Attribute	Type	Required	Description
`key`	expression	Yes	XPath expression evaluating to a single atomic value.
`select`	expression	No	XPath expression providing the map value. If absent, the content sequence constructor is used.

Examples

Building a map conditionally

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<config>
  <param name="timeout" value="30"/>
  <param name="debug" value="true"/>
  <param name="retries" value="3"/>
</config>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:map="http://www.w3.org/2005/xpath-functions/map">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/config">
    <xsl:variable name="settings">
      <xsl:map>
        <xsl:for-each select="param">
          <xsl:map-entry key="string(@name)" select="string(@value)"/>
        </xsl:for-each>
      </xsl:map>
    </xsl:variable>
    <resolved>
      <timeout><xsl:value-of select="map:get($settings, 'timeout')"/></timeout>
      <debug><xsl:value-of select="map:get($settings, 'debug')"/></debug>
    </resolved>
  </xsl:template>
</xsl:stylesheet>

Output:

<resolved>
  <timeout>30</timeout>
  <debug>true</debug>
</resolved>

Nested maps for structured data