ISTAT_INTERNAL
assert((pufbuf->istat & ISTAT_INTERNAL) == 0);
assert((pufbuf->istat & ISTAT_INTERNAL) == 0);
assert((pufbuf->istat & ISTAT_INTERNAL) == 0);
assert(from->istat & ISTAT_INTERNAL);
pufbuf->istat |= ISTAT_INTERNAL;
pufbuf->istat &= ~ISTAT_INTERNAL;