docs: def add_child(self, child):
          """
          Adds given child to the node.
  
          Usage::
  
              >>> node_a = AbstractCompositeNode("MyNodeA")
              >>> node_b = AbstractCompositeNode("MyNodeB")
              >>> node_a.add_child(node_b)
              True
              >>> node_a.children
              [<AbstractCompositeNode object at 0x10107afe0>]
  
          :param child: Child node.
          :type child: AbstractNode or AbstractCompositeNode or Object
          :return: Method success.
          :rtype: bool
          """
  
          self.__children.append(child)
          child.parent = self
          return True