[XQuery]&[F&O] fn:error: namespaces

Hello,

Andery and myself were discussing namespaces required to be given in function fn:error. 
http://www.w3.org/TR/xquery-operators/#func-error
 
We think that there are two possible problems out here. 
  
1. Default namespace : 
The XQuery draft does not define any standard namespace like "err" which would be present by default. 
Such kind of default namespace would be useful.  A namespace defined in the draft: http://www.w3.org/2004/07/xqt-errors/
does not give details of any error codes to be used.
If a default namespace err is provided, then user would not have to define the namespace explicitly when he/she wishes to do some error handling. 

2. User defined namespaces and error codes.
The draft does not speak much about how a user can define his own namespace and error codes for errors. 
Is it possible to do this in XQuery ? It would be great to have some information on this aspect in the draft.

Any comments from your side about the same would be very helpful. 

Regards,
Kanad.