Although ns must not be a relative URI, it can be ""

There's a bug in Section 3. It says:

"In addition to the attributes shown explicitly, any element can have an ns
attribute and any element can have a datatypeLibrary attribute. The value of
these attributes must match the anyURI symbol as described in the previous
paragraph. In addition, the value of these attributes must not use the
relative form of URI reference,..."

This incorrectly disallows empty strings as the value of ns and
datatypeLibrary (since an empty string is formally a relative URI).

James