XSLT Reference

xsl:expose

XSLT 3.0 element

Controls the visibility of components in an xsl:package, determining which are accessible to consuming packages.

Syntax

<xsl:expose component="function|template|variable|attribute-set|type|mode" match="*" visibility="public|private|final|abstract"/>

Description

xsl:expose is a top-level child of xsl:package that sets the visibility of one or more components. Without an xsl:expose declaration, all components in a package default to private visibility, meaning they are invisible to consuming stylesheets or packages.

The component attribute selects the type of component being configured, and the match attribute is a name pattern (supporting wildcards) that selects which components of that type are affected. The visibility attribute determines how the selected components may be used by packages that include this one via xsl:use-package.

The four visibility levels are:

public — accessible to consuming packages and may be overridden with xsl:override.
final — accessible but may not be overridden; the implementation is fixed.
private — hidden from consuming packages entirely.
abstract — declares the component’s signature but provides no implementation; consuming packages must supply one via xsl:override.

Parameters

Attribute	Type	Required	Description
`component`	token	Yes	Type of component: `function`, `template`, `variable`, `attribute-set`, `type`, or `mode`.
`match`	pattern	Yes	A name pattern selecting which components are affected. `*` matches all.
`visibility`	token	Yes	One of `public`, `private`, `final`, or `abstract`.

Return value

xsl:expose is a declaration; it produces no XDM value.

Examples

Exposing public functions and keeping helpers private

Package file:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:package
  name="com.example.strings"
  package-version="2.0"
  version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:str="com.example.strings">

  <!-- All functions public by default for this package -->
  <xsl:expose component="function" match="str:*" visibility="public"/>
  <!-- But the internal helper is final (visible but not overridable) -->
  <xsl:expose component="function" match="str:internal-*" visibility="final"/>

  <xsl:function name="str:title-case" as="xs:string">
    <xsl:param name="s" as="xs:string"/>
    <xsl:sequence select="str:internal-capitalize(lower-case($s))"/>
  </xsl:function>

  <xsl:function name="str:internal-capitalize" as="xs:string">
    <xsl:param name="s" as="xs:string"/>
    <xsl:sequence select="concat(upper-case(substring($s,1,1)), substring($s,2))"/>
  </xsl:function>

</xsl:package>

Using abstract visibility to define a required contract

<?xml version="1.0" encoding="UTF-8"?>
<xsl:package
  name="com.example.layout"
  package-version="1.0"
  version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <!-- render-header must be provided by each consuming package -->
  <xsl:expose component="template" match="xsl:template[@name='render-header']"
              visibility="abstract"/>

  <!-- render-page is public and calls the abstract render-header -->
  <xsl:expose component="template" match="xsl:template[@name='render-page']"
              visibility="public"/>

  <xsl:template name="render-header">
    <!-- Abstract: intentionally no default body -->
  </xsl:template>

  <xsl:template name="render-page">
    <html>
      <xsl:call-template name="render-header"/>
      <body><xsl:apply-templates/></body>
    </html>
  </xsl:template>

</xsl:package>

Consuming stylesheet providing the required implementation:

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

  <xsl:use-package name="com.example.layout" package-version="1.0">
    <xsl:override>
      <xsl:template name="render-header">
        <head><title>My Page</title></head>
      </xsl:template>
    </xsl:override>
  </xsl:use-package>

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

  <xsl:template match="/">
    <xsl:call-template name="render-page"/>
  </xsl:template>
</xsl:stylesheet>

Notes

Multiple xsl:expose declarations may appear in the same package. If a component matches more than one declaration, the most specific match (by name) takes precedence; the order of declaration is not significant.
The match attribute uses the same name-pattern syntax as xsl:apply-templates/@mode patterns. The wildcard * matches any expanded QName.
Abstract components must be overridden by every stylesheet that uses the package; failure to do so is a static error.
A final component may be accepted by a consuming package with xsl:accept using a less permissive visibility, but it cannot be overridden.