[Bug 3772] [XSLT 2.0] function-available cannot be used to detect extension functions

http://www.w3.org/Bugs/Public/show_bug.cgi?id=3772





------- Comment #1 from mike@saxonica.com  2006-09-27 10:20 -------
I think the spec makes an unstated assumption that an extension function is
present in the static context for use-when if and only if it is present in the
static context for the relevant part of the stylesheet. We should state this
assumption.

Suggested wording: in 3.12, in the table for static context components, in the
entry for in-scope functions, change "an implementation-defined set of
extension functions" to "the set of extension functions that are present in the
static context of every XPath expression (other than a use-when expression)
within the content of the element that is the parent of the use-when
attribute".

Also add a note: this ensures that function-available returns true in respect
of extension functions that can be called within the scope of the use-when
attribute. It also has the effect that these extension functions will be
recognized within the use-when attribute itself; however, the fact that a
function is available gives no guarantee that a call on the function will
succeed.