validate against multiple schemas

Hi,

This question follows up from a question a posted some months ago.
I want to validate against multiple schemas.  Is this possible?
For example, I have the following XML file:

<?xml version="1.0"?>
<patientRecord xmlns:hosp="http://www.swen.uwaterloo.ca/~mrbannon/HOSPITAL"
    xmlns:proto=http://www.swen.uwaterloo.ca/~mrbannon/PROTOTYPE
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <hosp:name proto:dataItem="true">
   <hosp:surname>Bannon</hosp:surname>
   <hosp:givenNames>Michael Ryan</hosp:givenNames>
   <hosp:title>Mr.</hosp:title>
  </hosp:name>
</hosp:patientRecord>

What I want to happen is for a parser to validate all the "hospial" elements agains the "hospital" schema and the "proto" attribute against the "proto" schema.  Right now, the www.w3c.org schema online validator says that proto:dataItem is undeclared.  Is there a way around this?  Can I tell a validator to validate ONLY THOSE ELEMENTS AND ATTRIBUTES THAT ARE MARKED WITH "hosp" AGAINST THE "hospital" schema and likewise for the "prototype" schema?

Thanks,

Ryan