Variables and parameters

- for reusing results of computations and parameterizing templates and whole stylesheets

static scope rules
can hold any XPath value (string, number, boolean, node-set) + result-tree fragment
purely declarative: variables cannot be updated
can be global or local to a template rule

Declaration:

<xsl:variable name="..." select="expression"/>: variable declaration for normal XPath value
<xsl:variable name="..."> template </..>: variable declaration for result tree fragment (template is instantiated to give value)
<xsl:param name="..." select="expression"/>: parameter declaration for normal XPath value (the value is the default value of the parameter)
<xsl:param name="..."> template </..>: parameter declaration for result tree fragment

Use:

$name: returns XPath value in expressions, e.g. attribute value templates (recall that XPath context contains variable bindings)
<xsl:with-param name=".." select="..."/> and <xsl:with-param name="..."> template </..>: passes parameters in xsl:call-template or xsl:apply-templates

Note: result tree fragments held by variables or parameters can be used as source in pattern matching and template instantiation!