noah_mendelsohn@u... wrote:

>As I noted above, there are serious discussions underway right now about 
>including XPath-based co-occurrence constraints in schema 1.1.   As with 
>the current use of Schematron in appinfo, these would be additional 
>constraints:  to be valid, content would have to satisfy both the content 
>model grammar and the XPath based constraints.   There are several 
>proposals as to exactly how the constraints would be expressed.  The ones 
>I believe closest to Schematron involve XPath predicates that would have 
>to resolve as true/false for the content to be valid per the type.  There 
>are also proposals from Fabio Vitale to use such predicates in selecting a 
>type.  So, no guarantee that anything will be proposed, but there is 
>certainly a chance.  We get requests for this function almost daily.
>  
>

Well, can I recommend just officialy recommending the  simple Schematron 
assert statements as the easiest way forward for everyone, using the 
schematron namespace, and inside <appinfo>

The ISO Schematron standard explicitly encourages this, see            
http://www.schematron.com/iso/P25.html#GEN38
including that you can define any context information for interpreting 
the XPath:
notably this includes type awareness.

I don't why this isn't a no-brainer: no need to alter XSD or add 
requirements to any
implementations, nicely layered, blame the limitations on someone else 
(me, ISO) when
people start to whinge,  no political ramifications with RELAX NG, etc.

Can fruit hang lower?

Rick