Method is_valid

extlibs/sol3/include/sol/sol.hpp:22283–22288

		}

		bool is_valid(std::false_type) {
			auto pp = stack::push_pop(tbl);
			auto p = stack::probe_get_field<std::is_same_v<meta::unqualified_t<Table>, global_table>>(lua_state(), key, lua_gettop(lua_state()));
			lua_pop(lua_state(), p.levels);
			return p;
		}

	public:
		Table tbl;