W_CAN_SCROLL
w->_flags &= ~W_CAN_SCROLL;
w->_flags |= W_CAN_SCROLL;
if (w->_flags & W_CAN_SCROLL) {
w->_flags &= ~W_CAN_SCROLL;
w->_flags |= W_CAN_SCROLL;
if (w->_flags & W_CAN_SCROLL) {
if (!(w->_flags & W_CAN_SCROLL))