'Return the next widget in the focus order which follows
widget which has currently the focus.
The focus order first goes to the next child, then to
the children of the child recursively and then to the
next sibling which is higher in the stacking order.  A
widget is omitted if it has the takefocus resource set
to 0.'

def tk_focusNext(self):

    name = self.tk.call('tk_focusNext', self._w)
    if (not name):
        return None
    else:
        return self._nametowidget(name)
