public static String registerNamespace(String namespaceURI, String suggestedPrefix)
            throws XMPException {
        return registry.registerNamespace(namespaceURI, suggestedPrefix);
    }
Register a namespace URI with a suggested prefix. It is not an error if the URI is already
registered, no matter what the prefix is. If the URI is not registered but the suggested
prefix is in use, a unique prefix is created from the suggested one. The actual registered
prefix is always returned. The function result tells if the registered prefix is the
suggested one.
Note: No checking is presently done on either the URI or the prefix.

@param namespaceURI    The URI for the namespace. Must be a valid XML URI.
@param suggestedPrefix The suggested prefix to be used if the URI is not yet registered. Must be a valid
                       XML name.
@return Returns the registered prefix for this URI, is equal to the suggestedPrefix if the
namespace hasn't been registered before, otherwise the existing prefix.
@throws XMPException If the parameters are not accordingly set
tika-xmp/src/main/java/org/apache/tika/xmp/XMPMetadata.java