Currently, because of the way the namespaces are defined for our KEW XSD files, it makes it impossible for an XML editor to validate them. For example, all of our XSD files include a reference to common.xsd but the only way to resolve it is by using our custom EntityResolver. It would be nice if the namespaces were defined in such a way that a tool could recognize these. In DTD you typically do this by having your DTD available at some URL. I'm not sure what the best practice is for XSD schemas.
When working on this, if we make changes to the schema namespace definitions we can preserve backward compatibility with existing XML by allowing our custom EntityResolver to still resolve the old entities.