TF_HOOK
#define TF_ACTIVITY (TF_GONE|TF_OPENED|TF_HOOK|TF_OPENCLOSE)
MPASS((tp->t_hook == NULL) == ((tp->t_flags & TF_HOOK) == 0));
if (tp->t_flags & TF_HOOK)
tp->t_flags |= TF_HOOK;
MPASS(tp->t_flags & TF_HOOK);
tp->t_flags &= ~TF_HOOK;
{ TF_HOOK, 's' },
{ TF_HOOK, 's' },