docs: def register_module(self, module, namespace=None):
          """
          Register a module.
  
          :param module: must be a string or a module object to register.
          :type module: str
          :param namespace: Namespace tag. If it is None module will be used as namespace tag
          :type namespace: str
          """
          namespace = namespace if namespace is not None else module \
              if isinstance(module, str) else module.__name__
          self.register_namespace(namespace, module)