Set the value of the ``<c:overlap>`` child element to *int_value*,
        or remove the overlap element if *int_value* is 0.

def overlap(self, value):
        """
        Set the value of the ``<c:overlap>`` child element to *int_value*,
        or remove the overlap element if *int_value* is 0.
        """
        if value == 0:
            self._element._remove_overlap()
            return
        self._element.get_or_add_overlap().val = value