cbs_peek_u
if (!cbs_peek_u(cbs, &v, 2))
return cbs_peek_u(cbs, out, 3);
return cbs_peek_u(cbs, out, 4);
if (!cbs_peek_u(cbs, &v, 2))
return cbs_peek_u(cbs, out, 3);
return cbs_peek_u(cbs, out, 4);