tsvalue
if (len != NULL) *len = tsvalue(o)->len;
case LUA_TSTRING: return tsvalue(o)->len;
else if (tsvalue(top-1)->len == 0) /* second operand is empty? */
else if (ttisstring(top-2) && tsvalue(top-2)->len == 0) {
size_t tl = tsvalue(top-1)->len;
size_t l = tsvalue(top-i-1)->len;
size_t l = tsvalue(top-i)->len;
setnvalue(ra, cast_num(tsvalue(rb)->len));
if (ttisstring(obj) && luaO_str2d(svalue(obj), tsvalue(obj)->len, &num)) {