Behaviour when unknown xsi:type or subst group member found

Hi,

Can you remind me what a schema enabled XML processor should do if it 
encounters an unknown xsi:type when parsing an instance?  Should it just 
skip over it, or flag an error etc.

Similarly, what is the desired behaviour when an unknown substitution group 
member is found (or an unknown element is encountered where a substitution 
group member element might be expected [I guess the element could be 
optional]).

Oh, and while I'm here, does the whitespace facet have any affect on 
attribute values, or are attribute values always collapsed?

Many thanks,

Pete Cordell
Codalogic Ltd
Interface XML to C++ the easy way using XML C++
data binding to convert XSD schemas to C++ classes.
Visit http://codalogic.com/lmx/ for more info