the XPath predicate is particularly intriguing, as the specified condition
'number(.)=number(.)' will always be true (all nodes for which it is true
that their content, when converted to a number, equals their own content
converted to a number)

This is not strictly true,
Michael Kay's Programmer's reference, second edition, page 90 says:
The equals operator +=; returns false if either or both oprands are NaN...

Regards,
Ragulf Pickaxe :)