[cddlm] CDL: extension and cdl:documentation

[Steve Loughran]

I would presume that both of the following operations are illegal

<?xml version="1.0"?>
<cdl:cdl 
xmlns:cdl="http://www.gridforum.org/namespaces/2005/02/cddlm/CDL-1.0">
   <cdl:documentation>
     Presumably, documentation cannot be extended.
   </cdl:documentation>
   <cdl:configuration>
     <cdl:documentation>
     do not expand these
     </cdl:documentation>

   </cdl:configuration>
   <cdl:system>
     <example cdl:extends="cdl:documentation"/>
   </cdl:system>
</cdl:cdl>

and

<?xml version="1.0"?>
<cdl:cdl 
xmlns:cdl="http://www.gridforum.org/namespaces/2005/02/cddlm/CDL-1.0">
   <cdl:documentation>
     In which a documentation node extends something.
     We should reject this.
   </cdl:documentation>
   <cdl:configuration>
     <example />

   </cdl:configuration>
   <cdl:system>
     <cdl:documentation cdl:extends="example">
     </cdl:documentation>
   </cdl:system>
</cdl:cdl>

These are extensions to and from documentation elements. My 
implementation does not (currently) resolve these; more by accident than 
design, and it doesnt give a very good error message as a consequence.

-steve