One backend on the 4.4BSD libc termios covers macOS, FreeBSD, NetBSD, OpenBSD and DragonFly. A speed_t there is the rate itself, so any rate is asked for by number; on macOS a rate the driver refuses through tcsetattr is retried through IOSSIOSPEED. Mark and space parity have no CMSPAR to express them and are refused. The module links libc on these targets, and `zig build check` now compiles the tests for each of them. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_012fcrFCsAeNziaz3Y5QR8E2