Saxon

XPath 4.0 allows function calls to provide argument values by keyword as well as positionally.

Some function libraries simply ignore any supplied keywords and interpret all arguments as positional. These include:

• constructor functions
• Java extension functions (both reflexive and integrated)
• The xsl:original pseudo-function
• Some libraries implemented as Java extension functions,

Some function libraries such as EXPath File and Binary are implemented as BuiltInFunctionSets, so keywords should work in principle, but no keyword data has been created, so using keywords will likely fail in unpredictable ways. It's not actually clear what we should do here: should we implement the parameter keywords defined in the spec, even though they were never intended to be used in this way?