Registers all the standard checkers in the given checker.

        If not present already, the standard checkers schema (STD_NAMESPACE) is
        added to the checker's namespace with an empty prefix.

def register_std(self):
        ''' Registers all the standard checkers in the given checker.

        If not present already, the standard checkers schema (STD_NAMESPACE) is
        added to the checker's namespace with an empty prefix.
        '''
        self._namespace.register(STD_NAMESPACE, '')
        for cond in _ALL_CHECKERS:
            self.register(cond, STD_NAMESPACE, _ALL_CHECKERS[cond])