'Add a ``get_or_change_to_x()`` method to the element class for this
child element.'

def _add_get_or_change_to_method(self):

    def get_or_change_to_child(obj):
        child = getattr(obj, self._prop_name)
        if (child is not None):
            return child
        remove_group_method = getattr(obj, self._remove_group_method_name)
        remove_group_method()
        add_method = getattr(obj, self._add_method_name)
        child = add_method()
        return child
    get_or_change_to_child.__doc__ = ('Return    the    ``<%s>``    child,    replacing    any    other    group    element    if    found.' % self._nsptagname)
    self._add_to_class(self._get_or_change_to_method_name, get_or_change_to_child)
