RBF_SERIAL
if ((opts & (RBF_MUTE|RBF_SERIAL|RBF_VIDEO)) == 0)
opts |= RBF_SERIAL|RBF_VIDEO;
if (opts & RBF_SERIAL) {
opts |= RBF_VIDEO | RBF_SERIAL;
if (opts & RBF_SERIAL)
if ((opts & RBF_SERIAL) && sio_ischar())