XSLT - match attribute

match attribute is one of the most important parts of XSLT, because it controls which XML nodes a template applies to.

1. What `match` Does

The match attribute of <xsl:template> contains an XPath pattern.
It tells the XSLT processor:
“This template applies whenever a node in the source XML matches this pattern.”
Patterns can be broad (match="*") or very specific (match="/library/book/title").

2. Basic Usage

<xsl:template match="book">
   <!-- What to output when a <book> element is encountered -->
</xsl:template>

This template applies whenever the processor encounters a <book> element in the XML.

3. Common Match Patterns

Pattern	Meaning
`/`	Matches the root node (the entire XML document).
`*`	Matches any element (wildcard).
`book`	Matches all `<book>` elements at any level.
`/library/book`	Matches `<book>` elements that are direct children of `<library>`.
`//book`	Matches all `<book>` elements anywhere in the document.
`book/title`	Matches `<title>` elements inside a `<book>`.
`@id`	Matches attributes named `id`.
`@*`	Matches any attribute.
`text()`	Matches text nodes (the actual text content inside elements).

4. Example

XML:

<library>
  <book id="b1">
    <title>1984</title>
    <author>George Orwell</author>
  </book>
  <book id="b2">
    <title>Brave New World</title>
    <author>Aldous Huxley</author>
  </book>
</library>

XSLT:

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

  <!-- Root template -->
  <xsl:template match="/">
    <html>
      <body>
        <h2>Library</h2>
        <xsl:apply-templates/>
      </body>
    </html>
  </xsl:template>

  <!-- Match the <library> element -->
  <xsl:template match="library">
    <ul>
      <xsl:apply-templates/>
    </ul>
  </xsl:template>

  <!-- Match <book> elements -->
  <xsl:template match="book">
    <li>
      <xsl:value-of select="title"/> 
      (<xsl:value-of select="author"/>)
    </li>
  </xsl:template>

</xsl:stylesheet>

Output:

<html>
  <body>
    <h2>Library</h2>
    <ul>
      <li>1984 (George Orwell)</li>
      <li>Brave New World (Aldous Huxley)</li>
    </ul>
  </body>
</html>

5. Match Precedence

If two templates could match the same node, the most specific one wins.
Example:
```
<xsl:template match="book"> ... </xsl:template>
<xsl:template match="library/book"> ... </xsl:template>
```
- For <book> inside <library>, the second template (library/book) will apply because it’s more specific.

6. Key Takeaways

match="/" → starting point (root).
match="elementName" → handles specific elements.
match="@attrName" → handles attributes.
match="*" or @* → wildcard patterns.
More specific patterns override general ones.