 <p>the usage of ccc:fid is an extension of the namespace which needs to be declared in xml in order to be able to use it in libraries like simplexml. </p> <p>Here are some examples of descriptions of usin a namespace:</p> <ul> <li><a href="http://www.w3.org/TR/1999/REC-xml-names-19990114/" rel="nofollow noreferrer">http://www.w3.org/TR/1999/REC-xml-names-19990114/</a></li> <li><a href="http://www.w3.org/TR/xml-names/" rel="nofollow noreferrer">http://www.w3.org/TR/xml-names/</a></li> </ul> <p>Hope that helps, albeit it is a little complicated. </p>