RE: document() function and error-handling

> I'd love to see a reference to the "rule elsewhere". 

It doesn't take long to find it, just do CTRL-F "reserved".

[Definition: A Name is a token beginning with a letter or one of a few
punctuation characters, and continuing with letters, digits, hyphens,
underscores, colons, or full stops, together known as name characters.]
Names beginning with the string "xml", or with any string which would match
(('X'|'x') ('M'|'m') ('L'|'l')), are reserved for standardization in this or
future versions of this specification.

> There's a rule, that every qname starting with a prefix xml isn't OK. 

You're making that up, the XML 1.0 Recommendation doesn't know about QNames.

Michael Kay
http://www.saxonica.com/