@Override
    public DatatypeLibrary createDatatypeLibrary(String namespaceURI) {
        if (NAMESPACE.equals(namespaceURI)) {
            return new Html5DatatypeLibrary();
        }
        return null;
    }
Returns a <code>Html5DatatypeLibrary</code> on the library namespace and <code>null</code>
otherwise.
@param namespaceURI a namespace URI
@return a <code>DatatypeLibrary</code> or <code>null</code>
@see org.relaxng.datatype.DatatypeLibraryFactory#createDatatypeLibrary(java.lang.String)
src/nu/validator/datatype/Html5DatatypeLibraryFactory.java