THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

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, value given by XPath expression
<xsl:variable name="..."> template </..>
variable declaration, template is instantiated as result tree fragment to give value

- similarly for xsl:param parameter declarations (where the specified values act as defaults).

Use:

$name
returns XPath value in expressions, e.g. attribute value templates
xsl:with-param
passes parameters in xsl:call-template and xsl:apply-templates

Example 1:

<xsl:template match="foo"> <xsl:variable name="X" select="42"/> <xsl:variable name="Y"> <sometag><xsl:value-of select="@bar"/></sometag> </xsl:variable> <first> <xsl:value-of select="$X"/> <xsl:copy-of select="$Y"/> </first> <second> <xsl:value-of select="$X"/> <xsl:copy-of select="$Y"/> </second> </xsl:template>

Example 2:

... <xsl:apply-templates select="item"> <xsl:with-param name="COLOR" select="'blue'"/> </xsl:apply-templates> ... <xsl:template match="item"> <xsl:param name="COLOR" select="'black'"/> <font color="{$COLOR}"> <xsl:apply-templates/> </font> </xsl:template>

the mechanism for assigning values to top-level (global) parameters is implementation dependent
unfortunately, result tree fragments in variables cannot be used as source for pattern matching and template instantiation - so general composition of transformations is not possible within a single stylesheet :-(