[relax-ng] Why annotations are allowed in <empty/> and not in <ref/>?

Just being curious...

Why are annotations allowed in some empty content elements (such as
"empty") and not in some othet (such as "ref" and "parentRef")?

Thanks

Eric
-- 
See you in London for XML Europe.
                                                http://www.xmleurope.com
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Eric van der Vlist       http://xmlfr.org            http://dyomedea.com
(W3C) XML Schema ISBN:0-596-00252-1 http://oreilly.com/catalog/xmlschema
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