In this concluding article, expand your XSLT vocabulary by exploring conditional constructs, loops, variables, and numbering, together with examples and illustrations of how these programming capabilities can substantially simplify your XSLT experience.
Just as XML has entities, pre-defined constants which can be used at different places within your document, so too does XSLT have variables. However, XSLT variables are not the same as the ones you may be used to working with in standard programming languages. XSLT variables, once defined, cannot be altered; they remain static and can merely be used at different places within the XSLT stylesheet.
XSLT variables are defined with the <xsl:variable> instruction, and a value is attached to them either via a "select" attribute or enclosed within the opening and closing tags of the instruction; this value may be a literal, or obtained from an expression. In case a variable lacks both a "select" attribute and a content value, it is automatically assigned an empty string value.
Variables may be defined either within or outside template rules. A variable defined outside a template rule (at the top-level of the document) is globally available, while a variable defined within a template rule is available only to descendants of that rule.
Once defined, variables can be accessed by referencing the variable name with a preceding dollar($) symbol.
Consider the following stylesheet, again with reference to the preceding XML data.
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:variable
name="flavour">strawberry</xsl:variable>
<xsl:template match="/">
<html>
<head>
<body>
--
root level -- My favourite flavour is <xsl:value-of select="$flavour"
/><br
/>
<xsl:apply-templates select="recipe/ingredients" />
<xsl:apply-templates
select="recipe/process" />
-- root level -- My favourite flavour is <xsl:value-of
select="$flavour"
/><br />
</body>
</head>
</html>
</xsl:template>
<xsl:template
match="ingredients/item">
<xsl:variable name="flavour">raspberry</xsl:variable>
--
item level -- My favourite flavour is <xsl:value-of select="$flavour"
/><br
/>
</xsl:template>
<xsl:template match="process/step">
-- step level --
My favourite flavour is <xsl:value-of select="$flavour"
/><br />
</xsl:template>
</xsl:stylesheet>
Here, I've first set up a global variable, $flavour, with the value "strawberry".
I've displayed it in my very first template rule, which matches the document root. Since this template rule does not contain any overriding variable definition, it will use and print the value of the global variable, "strawberry".
Then I've transferred control to the second template rule, which matches "item" elements. Over here, I've defined a new value for the variable, "raspberry". This time, the value of the global variable will be superseded by the value within the template rule, and an attempt to print $flavour will return "raspberry".
Once that node collection is exhausted, control goes to the third template rule, which matches "step" elements. This rule does not contain any variable definition; further, it does not have access to the value defined within the second template rule, since it is not a direct descendant of that rule. Consequently, it will also use the value "strawberry".
Here's the output:
-- root level -- My favourite flavour is strawberry
-- item level -- My favourite
flavour is raspberry
-- item level -- My favourite flavour is raspberry
-- item
level -- My favourite flavour is raspberry
-- step level -- My favourite flavour
is strawberry
-- step level -- My favourite flavour is strawberry
-- step level
-- My favourite flavour is strawberry
-- step level -- My favourite flavour is
strawberry
-- step level -- My favourite flavour is strawberry
-- step level --
My favourite flavour is strawberry
-- root level -- My favourite flavour is strawberry
/ 6 
