Re: Checking if an extension function exists and implementation/version sniffing

Eric,

We discussed this during our last XForms call.

We discussed two solutions:

1. Import the XSLT 2 function-available() function:

http://www.w3.org/TR/xslt20/#function-function-available

Note that XPath 3 now has function-lookup(), but this cannot be used
with XPath 2 as this requires support for function() items:

http://www.w3.org/TR/2013/CR-xpath-functions-30-20130108/#func-function-lookup

2. Improved error handling in XForms

This is a separate but related topic. XPath and action errors should
be, at least optionally, recoverable. This way, if you have a an error
in an action which uses an unknown function, you could recover from
that, and deduct that there was an issue with an XPath expression.

#1 would be easy, both at the spec level and for implementors. This
would also be the most direct solutions to your requirement.

#2 is more involved, but also more useful, and a more indirect way,
and solves in general a slightly different problem.

My proposal would be to do both for XForms 2.0. I have an action item
to make a proposal for improved error handling already.

Please let us know if you have any comments on this!

-Erik