Attribute indicating the tree coordinates for this node.

        The tree coordinates of a node are expressed as a tuple of the
        indices of the node and its ancestors, for example:
        A grandchild node with node path 
        `/root.name/root.childs[2].name/root.childs[2].childs[0].name` 
        would have coordinates `(2,0)`.
        The root node _coord is an empty tuple: `()`

        :returns: the tree coordinates for this node.
        :rtype: tuple

def _coord(self):
        """Attribute indicating the tree coordinates for this node.

        The tree coordinates of a node are expressed as a tuple of the
        indices of the node and its ancestors, for example:
        A grandchild node with node path 
        `/root.name/root.childs[2].name/root.childs[2].childs[0].name` 
        would have coordinates `(2,0)`.
        The root node _coord is an empty tuple: `()`

        :returns: the tree coordinates for this node.
        :rtype: tuple 
        """
        _coord = []
        _node = self
        while _node.parent:
            _idx = _node.parent.childs.index(_node)
            _coord.insert(0, _idx)
            _node = _node.parent
        return tuple(_coord)