xsl:evaluate

The xsl:evaluate instruction is new in XSLT 3.0. It allows dynamic evaluation of XPath expressions constructed as a string, in the same way as the saxon:evaluate() extension function that has been available in Saxon for many years.

The following example sorts product elements according to a sort key supplied (in the form of an XPath expression) as a parameter to the stylesheet.

The functionality is available as an XSLT instruction, rather than a function, to allow more flexibility in the syntax, in particular the ability to define parameters using xsl:with-param child elements.

The instruction has been fully implemented since Saxon 9.3 with the following exceptions:

• Functions available only in XSLT, such as key(), cannot be used in the target XPath expression.

The instruction may take an xsl:fallback to define fallback behaviour when using an XSLT 2.0 processor.

Attributes:

• xpath: an expression, which is evaluated to return the target expression as a string.

• base-uri: a string (as an AVT), gives the base URI for the target expression. Defaults to the base URI of the stylesheet instruction.

• namespace-context: an expression returning a node; the in-scope namespaces of this node define the namespace context for the XPath expression. Defaults to the namespace context of the xsl:evaluate instruction in the stylesheet

• as: a SequenceType: defines the required type of the result of the XPath expression. Defaults to item()*

• schema-aware: "yes" or "no", as an AVT: if "yes", the XPath expression has access to the schema components imported into the stylesheet.

Children:

• xsl:with-param: defines variables that the target expression can use.

• xsl:fallback: defines fallback behaviour when using an XSLT 2.0 (or 1.0) processor.