XSLT Reference

xsl:use-accumulators

XSLT 3.0 element

Declares which accumulators are active for a streaming template or mode, enabling the processor to compute only necessary values.

Syntax

<xsl:use-accumulators value="accumulator-name-list"/>

Description

xsl:use-accumulators is an attribute (expressed as a pseudo-element in older descriptions, but in current XSLT 3.0 it is an attribute on xsl:template or xsl:mode) that lists the accumulators that should be active while processing a streaming template. When streaming is in use, the XSLT processor cannot maintain all accumulators simultaneously because it processes nodes in document order without storing the full tree. Declaring which accumulators are needed allows the processor to activate only those, reducing memory and processing overhead.

In practice, xsl:use-accumulators appears as the use-accumulators attribute on an xsl:template or xsl:mode element. The value is a whitespace-separated list of accumulator names (QNames). Only accumulators listed here are guaranteed to return meaningful values via accumulator-before() and accumulator-after() within the template’s scope.

If use-accumulators is absent on a streaming template, no accumulators are active by default. In non-streaming stylesheets, all accumulators defined in the stylesheet are available without declaring them.

Parameters

Attribute	Context	Type	Description
`use-accumulators`	`xsl:template` or `xsl:mode`	`xs:QName*` whitespace-separated	Names of accumulators to activate for this template or mode.

Return value

xsl:use-accumulators is a declaration attribute; it produces no XDM value.

Examples

Streaming a large document and reading a running total accumulator

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">

  <xsl:output method="xml" indent="yes"/>

  <!-- Define an accumulator that sums sale amounts -->
  <xsl:accumulator name="running-total" as="xs:decimal" initial-value="0">
    <xsl:accumulator-rule match="sale" select="$value + xs:decimal(@amount)"/>
  </xsl:accumulator>

  <!-- Streaming template: declare which accumulators are needed -->
  <xsl:template match="/" use-accumulators="running-total">
    <xsl:source-document streamable="yes" href="sales.xml">
      <report>
        <xsl:apply-templates select="sales/sale"/>
        <total><xsl:value-of select="accumulator-after('running-total')"/></total>
      </report>
    </xsl:source-document>
  </xsl:template>

  <xsl:template match="sale" use-accumulators="running-total">
    <sale amount="{@amount}"
          running="{accumulator-after('running-total')}"/>
  </xsl:template>
</xsl:stylesheet>

Input XML (sales.xml):

<?xml version="1.0" encoding="UTF-8"?>
<sales>
  <sale amount="100.00"/>
  <sale amount="250.50"/>
  <sale amount="75.25"/>
</sales>

Output:

<report>
  <sale amount="100.00" running="100.00"/>
  <sale amount="250.50" running="350.50"/>
  <sale amount="75.25" running="425.75"/>
  <total>425.75</total>
</report>

Using multiple accumulators in a streaming mode

<?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">

  <xsl:output method="xml" indent="yes"/>

  <xsl:accumulator name="item-count" as="xs:integer" initial-value="0">
    <xsl:accumulator-rule match="item" select="$value + 1"/>
  </xsl:accumulator>

  <xsl:accumulator name="total-price" as="xs:decimal" initial-value="0">
    <xsl:accumulator-rule match="item" select="$value + xs:decimal(@price)"/>
  </xsl:accumulator>

  <!-- Activate both accumulators for this streaming mode -->
  <xsl:mode name="stream-mode" streamable="yes"
            use-accumulators="item-count total-price"/>

  <xsl:template match="/" use-accumulators="item-count total-price">
    <xsl:source-document streamable="yes" href="order.xml">
      <xsl:apply-templates select="order" mode="stream-mode"/>
    </xsl:source-document>
  </xsl:template>

  <xsl:template match="order" mode="stream-mode">
    <summary>
      <count><xsl:value-of select="accumulator-after('item-count')"/></count>
      <total><xsl:value-of select="accumulator-after('total-price')"/></total>
    </summary>
  </xsl:template>
</xsl:stylesheet>