code: def addchild(self, child):
          
          if not self.accept_children:
              return False
          self.children += [child]
          return True
docs: Add a new child to the command
  
          A child corresponds to a command located into a block (this
          command's block). It can be either an action or a control.
  
          :param child: the new child
          :return: True on succes, False otherwise