RE: schemas: can I restrict an elem's content based on att value

["Arnold, Curt" <Curt.Arnold@hyprotech.com>]

I actually did find a statement where xsi:type is required to be derived from the declared type in Section 3.3:

If there is an attribute information item among the element information item's [attributes] whose [namespace URI] is identical to http://www.w3.org/2000/10/XMLSchema-instance and whose [local name] is
type, 
then 
...
2.3  The local type definition is validly derived from the {type definition} given the {disallowed substitutions}, as defined in Type Derivation OK (Complex) (§5.11) (if it is a complex type
definition), or as defined in Type Derivation OK (Simple) (§5.12) (if it is a simple type definition).  

However that doesn't jump out at you if you do a search for "xsi:type".

If it doesn't get into the prose, at least it would be nice to put xsi:null and xsi:type into some of these dense text so that you can find them with a search.

EG: something like
--------

If there is an attribute information item among the element information item's [attributes] whose [namespace URI] is identical to http://www.w3.org/2000/10/XMLSchema-instance and whose [local name] is
type (informally xsi:type), then 

2.1  The normalized value of ....