XSLT, 2nd Edition

Defining a Key with <xsl:key>

You define a key() function with the <xsl:key> element:

<xsl:key name="supplier-by-country" match="supplier" use="@country"/>
<xsl:key name="part-by-supplier" match="part" use="@supplier"/>

The key has three attributes:

name

This attribute is used to refer to this particular key. When you want to find parts of your XML document, use the name to indicate the key you want to use.

match

Containing an XPath expression, this attribute specifies what part of the document you want to index. In our sample here, we’ve created two keys: one for retrieving <supplier>s and one for retrieving <part>s.

use

Containing another XPath expression, this attribute is interpreted in the context of the match attribute. In other words, the first <xsl:key> element here, named supplier-by-country, creates an index of all the <supplier> elements, and uses the country attribute to retrieve them. The second <xsl:key> element, named part-by-supplier, creates an index of all the <part> elements and uses the supplier attribute to find them.

[2.0] XSLT 2.0 adds a fourth attribute, collation. This allows us to specify a set of rules for how values are compared. To cite a frequent example from the specs, the German word for street can be spelled Strasse or Straße. Using a German collation for the key function causes those to words to be the same, despite the fact that they are clearly different strings.

Note

The XSLT 1.0 specification specifically states that the match and use attributes can’t ...