docs: def get_node_by_coord(self, coord, relative=False):
          """Get a node from a node coord. 
  
          :param coord: the coordinates of the required node.
          :type coord: tuple or list
          :param relative: `True` if coord is relative to the node instance,
              `False` for absolute coordinates.
          :type relative: bool
          :returns: the node corresponding to `coord`.
          :rtype: Node or None
          """
          if not isinstance(coord, (list, tuple)) or False in list(map(lambda i: type(i)==int, coord)):
              logger.warning("%s.get_node_by_coord: node«%s», arg «coord»=«%s», «coord» must be list or tuple of integers." % (self.__class__.__name__, self.name, coord))
              return None
          if relative:
              _node = self
          else:
              _node = self._root # _node = self.get_rootnode()
          for idx in coord:
              _node = _node.childs[idx]
              if _node is None:
                  logger.warning("%s.get_node_by_coord: node«%s», arg «coord»=«%s» not valid." % (self.__class__.__name__, self.name, coord))
                  return None
          return _node