🔁 XSLT <xsl:apply-templates> – Trigger Template Matching for XML Nodes
🧲 Introduction – Why Learn <xsl:apply-templates>?
If <xsl:template> defines what to do with a node, then <xsl:apply-templates> tells XSLT when and where to do it. It’s used to recursively process XML elements, triggering the right templates based on node structure. This makes your XSLT code modular, reusable, and scalable—especially for large or nested XML documents.
🎯 In this guide, you’ll learn:
- What
<xsl:apply-templates>does - How it works with
<xsl:template match="..."> - How to apply templates to specific child nodes
- Best practices and use cases for recursive processing
🧾 Syntax of <xsl:apply-templates>
<xsl:apply-templates select="XPathExpression"/>
select: (optional) An XPath expression targeting nodes to process- If omitted: Applies to all child nodes of the current context node
📄 Sample XML
<catalog>
<book id="101">
<title>Learn XSLT</title>
<author>Jane Doe</author>
</book>
</catalog>
✅ Example – Basic Template Application
<xsl:template match="/catalog">
<html>
<body>
<h2>Book Catalog</h2>
<xsl:apply-templates select="book"/>
</body>
</html>
</xsl:template>
<xsl:template match="book">
<div>
<h3><xsl:value-of select="title"/></h3>
<p><xsl:value-of select="author"/></p>
</div>
</xsl:template>
✅ Result:
<h2>Book Catalog</h2>
<div>
<h3>Learn XSLT</h3>
<p>Jane Doe</p>
</div>
🔁 Apply Templates Recursively
If you want to process all children:
<xsl:apply-templates/>
✅ This is commonly used in the root template to start the transformation.
🔍 Applying to Specific Children
<xsl:apply-templates select="book/title"/>
✅ Only applies templates to <title> inside <book>, ignoring other children.
🧠 Example – Combining with Sorting
<xsl:apply-templates select="catalog/book">
<xsl:sort select="title" data-type="text"/>
</xsl:apply-templates>
✅ Applies templates to books, sorted alphabetically by title.
⚖️ <xsl:apply-templates> vs <xsl:for-each>
| Feature | <xsl:apply-templates> | <xsl:for-each> |
|---|---|---|
| Output control | Delegated to matched templates | Controlled inline |
| Recursion | ✅ Supports nested templates | ❌ No recursion |
| Template reuse | ✅ Yes | ❌ No |
| Best for | Structured, nested XML | Flat, repeatable structures |
✅ Best Practices for <xsl:apply-templates>
- ✔️ Use for recursive XML structures (e.g., nested menus, chapters)
- ✔️ Combine with multiple
<xsl:template match="...">blocks - ✔️ Use
select="..."to limit scope when needed - ❌ Don’t hardcode output within templates that should be reusable
📌 Summary – Recap & Next Steps
<xsl:apply-templates> enables elegant, recursive, and reusable XML transformations. It works hand-in-hand with <xsl:template> to process nodes based on structure rather than hardcoded logic—just like a stylesheet in HTML/CSS.
🔍 Key Takeaways:
- Triggers template matching for specific or all child nodes
- Supports recursion and modular transformations
- Ideal for processing nested XML with reusable rules
⚙️ Real-world relevance: Used in XML-to-HTML renderers, documentation generators, XML viewers, and dynamic content systems.
❓ FAQs – XSLT <apply-templates>
❓ What does <xsl:apply-templates> do?
✅ It applies matching templates to the current node’s children or to nodes specified in select.
❓ Can I apply templates to multiple nodes?
✅ Yes. Use XPath in select to match a node set.
❓ Is <xsl:apply-templates> recursive?
✅ Yes. It’s the primary way to implement recursion in XSLT.
❓ How is this different from <xsl:for-each>?
✅ <xsl:for-each> outputs inline; <xsl:apply-templates> delegates to matched templates.
❓ Do I need a template for every node?
✅ Only if you want to control how it’s rendered—otherwise, unmatched nodes are ignored.
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