code: @Override
      public DatatypeLibrary createDatatypeLibrary(String namespaceURI) {
          if (NAMESPACE.equals(namespaceURI)) {
              return new Html5DatatypeLibrary();
          }
          return null;
      }
docs: 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)