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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def activate(self, page=None):
 """Activates overlay with browser, optionally opened at a given page. :param str page: Overlay page alias (see OVERLAY_PAGE_*) or a custom URL. """

        page = page or ''

        if '://' in page:
            self._iface.activate_overlay_url(page)

        else:
            self._iface.activate_overlay_game(page)