code: def register_bjam_action (self, action_name, function=None):
          
  
          # We allow duplicate calls to this rule for the same
          # action name.  This way, jamfile rules that take action names
          # can just register them without specially checking if
          # action is already registered.
          assert isinstance(action_name, basestring)
          assert function is None or callable(function)
          if action_name not in self.actions:
              self.actions[action_name] = BjamNativeAction(action_name, function)
docs: Informs self that 'action_name' is declared in bjam.
  
          From this point, 'action_name' is a valid argument to the
          set_update_action method. The action_name should be callable
          in the global module of bjam.