Format XSLT Stylesheets — Templates, Match Patterns, and Output

Q: Format XSLT Stylesheets — Templates, Match Patterns, and Output

## Formatting XSLT Stylesheets XSLT (Extensible Stylesheet Language Transformations) stylesheets are XML documents that define rules for transforming XML into other formats (XML, HTML, text). XSLT files are notoriously difficult to read without proper formatting. ### Basic XSLT Structure xml <h1

Format XSLT stylesheet XML for readability. Understand template rules, match patterns, xsl:apply-templates, xsl:for-each, output methods, and how proper formatting aids XSLT debugging.

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Detailed Explanation

Formatting XSLT Stylesheets

XSLT (Extensible Stylesheet Language Transformations) stylesheets are XML documents that define rules for transforming XML into other formats (XML, HTML, text). XSLT files are notoriously difficult to read without proper formatting.

Basic XSLT Structure

<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

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

  <xsl:template match="/">
    <html>
      <body>
        <h1><xsl:value-of select="/catalog/title" /></h1>
        <xsl:apply-templates select="/catalog/book" />
      </body>
    </html>
  </xsl:template>

  <xsl:template match="book">
    <div class="book">
      <h2><xsl:value-of select="title" /></h2>
      <p>Price: <xsl:value-of select="price" /></p>
    </div>
  </xsl:template>

</xsl:stylesheet>

Template Rules

Each <xsl:template> defines a transformation rule for elements matching its match attribute (an XPath expression). Formatting should clearly separate template rules with blank lines and consistently indent their content.

XSLT Instructions

Common XSLT instructions that benefit from clear indentation:

<xsl:for-each select="..."> — iteration
<xsl:if test="..."> — conditional
<xsl:choose> / <xsl:when> / <xsl:otherwise> — multi-branch conditional
<xsl:variable name="..."> — variable declaration
<xsl:call-template name="..."> — named template invocation

Mixed Content Challenge

XSLT often contains mixed content — XSLT instructions interspersed with literal output markup (HTML tags, text). Formatting must handle both the XSLT logic structure and the output template structure:

<xsl:template match="item">
  <tr>
    <td><xsl:value-of select="name" /></td>
    <td>
      <xsl:choose>
        <xsl:when test="@status = 'active'">
          <span class="active">Active</span>
        </xsl:when>
        <xsl:otherwise>
          <span class="inactive">Inactive</span>
        </xsl:otherwise>
      </xsl:choose>
    </td>
  </tr>
</xsl:template>

XPath Expressions in Attributes

XSLT heavily uses XPath expressions in select, test, and match attributes. These expressions can be long and complex. While the formatter cannot break attribute values across lines, consistent element indentation provides the visual structure needed to follow the transformation logic.

Use Case

XSLT formatting is crucial for developers maintaining XML transformation pipelines in publishing systems, data integration platforms, and enterprise middleware. Readable XSLT makes it possible to trace how source XML maps to output, debug transformation errors, and refactor complex template hierarchies.

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