XSLT Reference

current-merge-group()

XSLT 3.0 node function

Returns the sequence of items in the current merge group inside an xsl:merge-action block.

Syntax

current-merge-group(source?)

Description

current-merge-group() is used inside the xsl:merge-action child of an xsl:merge instruction. It returns the sequence of items from the current merge group — that is, all items from one or more merge sources that share the same current merge key.

When xsl:merge processes multiple input streams simultaneously, it groups corresponding items by their computed merge key. Inside xsl:merge-action, current-merge-group() without an argument returns all items from all sources in the current group. When a source argument is supplied (the value of a for-each-source attribute or a source name), the function returns items only from that specific merge source.

Parameters

Parameter	Type	Required	Description
`source`	xs:string	No	The name of the merge source to restrict the group to. Omit to get items from all sources.

Return value

item()* — the items in the current merge group, optionally restricted to a named source.

Examples

Merging two sorted lists

Input XML (file1.xml):

<?xml version="1.0" encoding="UTF-8"?>
<items>
  <item key="a">Alpha from source1</item>
  <item key="b">Beta from source1</item>
</items>

Input XML (file2.xml):

<?xml version="1.0" encoding="UTF-8"?>
<items>
  <item key="a">Alpha from source2</item>
  <item key="c">Gamma from source2</item>
</items>

Stylesheet:

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

  <xsl:template match="/">
    <merged>
      <xsl:merge>
        <xsl:merge-source name="s1" select="doc('file1.xml')/items/item">
          <xsl:merge-key select="@key"/>
        </xsl:merge-source>
        <xsl:merge-source name="s2" select="doc('file2.xml')/items/item">
          <xsl:merge-key select="@key"/>
        </xsl:merge-source>
        <xsl:merge-action>
          <group key="{current-merge-key()}">
            <xsl:for-each select="current-merge-group()">
              <item><xsl:value-of select="."/></item>
            </xsl:for-each>
          </group>
        </xsl:merge-action>
      </xsl:merge>
    </merged>
  </xsl:template>
</xsl:stylesheet>

Output:

<merged>
  <group key="a">
    <item>Alpha from source1</item>
    <item>Alpha from source2</item>
  </group>
  <group key="b">
    <item>Beta from source1</item>
  </group>
  <group key="c">
    <item>Gamma from source2</item>
  </group>
</merged>

Reading from a specific source

Stylesheet snippet:

<xsl:merge-action>
  <!-- Only items from source s1 -->
  <xsl:for-each select="current-merge-group('s1')">
    <s1-item><xsl:value-of select="."/></s1-item>
  </xsl:for-each>
</xsl:merge-action>

Notes

current-merge-group() is only valid inside the xsl:merge-action element; using it elsewhere raises a static error.
Without an argument, it returns items from all named merge sources combined.
The merge sources must provide pre-sorted input or declare sort keys via xsl:merge-key for xsl:merge to operate correctly.
current-merge-group() and current-merge-key() are the two functions designed specifically for use inside xsl:merge-action.