> Given that (as surely every XSLT programmer learned in XSLT 
> school) "." is 
> short for "self::node()", I should think this match would 
> give you an error 
> in a conformant processor.
> 

Correct. Quite apart from the fact that the self axis can't be used in
patterns, "." is not a legal pattern according to the grammar.

Michael Kay