XML Schema namespace association at the API level

Hi,

Most processors I'm familiar with allow some sort of association of schemas
with namespaces via the API so that one can have a list of schemas maintained
by the API seperate from the actual Schemas, allowing the Processor to take
care of scenarios such as 
Schema # 1 uses xsd:any with processContents= strict when content of the
document at the point where xsd:any is allowed is in namespace x without
Schema #1 referencing Schema #2 which validates x directly. 

This basically gives the same capability that one can have with
xsi:schemaLocation at the instance to the application. 

The thing I'm wondering about is, is this capacity defined anywhere in the
XML Schema specs? I'm looking in "4 Schemas and Namespaces: Access and
Composition" http://www.w3.org/TR/xmlschema-1/#composition and I can't find
anything. Anywhere else? Different Processors seem to implement this
differently, and it doesn't seem to me to be the kind of thing that one would
require of a spec, thus my question. Hope this question was clear.

Cheers,
Bryan Rasmussen