When working with XML, I often encountered attribute values that are qualified with a namespace, for example:
<tag xmlns:foo="http://foo.bar" att1="foo:value" />
I always wondered how far (or if at all) this is covered by the XML standard. The parsers I tried (Xerces and Saxon in Java or the XMLSpy's native parser) still report the XML as well formed even if you leave out a namespace declaration that is referenced in an attribute value.
So my question is: Is this usage of namespaces in attribute values covered by the XML standard (or an extension to it) or is it entirely up to the application's business logic to deal with it? ...also, if it is a standard, can you get any java parser to correctly check if a namespace prefix in an attribute value is correctly declared?