query regarding validity of RDF file

Is a tag like this permissible in RDF?

<rdf:RDF 
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" 
    xmlns:lib="http://www.zvon.org/library"> 

The formal grammar for RDF would seem to say no:

RDF     ::= ['<rdf:RDF>'] obj* ['</rdf:RDF>']

ie you can't declare namespaces as attributes of the root element of an RDF document.