[xsl] Can an element have 2 namespaces?

[cert21 <cert21@xxxxxxx>]

I am having trouble parsing this rss 1.0 feed
The reason is that it appears that there are 2 different namespaces 
declared in the root document

This is how the document starts:

<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"; xmlns:dc="http://purl.org/dc/elements/1.1/"; xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"; xmlns:admin="http://webns.net/mvcb/"; xmlns="http://purl.org/rss/1.0/";>

The parser (in php, a DOMDocument class) reports the namespace to be

http://www.w3.org/1999/02/22-rdf-syntax-ns#

but why then they declared another namespace with 
xmlns="http://purl.org/rss/1.0/";

Is it even a valid way to declare 2 namespaces together like this?

Anyway, which one is considered to be the correct one?