How do I validate against a schema?

I am using the following script to check that a document entered on a form
is well formed, however I would also like to validate it against the
schema.  Is there some way to do this?  Everything I have seen so far only
appears to validate against DTDs.

Thanks
Adrian

   <script>
    function f() {
      var val = theform.doc.value;
      var test = new ActiveXObject("Microsoft.XMLDOM");
      test.async = false;
      test.loadXML(val);
      err = test.parseError;
      if (err != 0) {
       ErrorMsg =  "Your XML Document is not Well Formed.\n" +
                    err.srcText + "\n" + "Line " + err.line + ", Pos " + 
                    err.linepos + "\n" + err.reason;
       alert(ErrorMsg);
       test = null;
       event.returnValue  = false;
      }
    }
   </script>



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