> in your XML-Documet change //$xrd*($v*2.0) to a valid URI Websearching for "URI RFC" will find the formal specification for URIs, including the grammar that defines what is and isn't legal; namespace names must meet the syntactic constraints of URI References. You may have to escape some characters (and your tool may have to be able to handle escaped characters) if you really need to pass that sort of information through your namespace names.
Also note, while I'm writing, that per the XML Namespaces Recommendation " The empty string, though it is a legal URI reference, cannot be used as a namespace name. The use of relative URI references, including same-document references, in namespace declarations is deprecated. "
