- New allowclipboard config flag (default on) so OSC 52 works without
enabling all window ops. tmux set-clipboard was silently dropped before.
- DA2 (CSI >c) and DA3 (CSI =c) answered; tmux fingerprints with these.
- DSR 996 reports the colour scheme (dark/light) from the background.
- DECRQM 2031 reported as permanently reset.
- Unknown DCS sequences (DCS tmux; passthrough, XTGETTCAP) are discarded
until ST instead of having their body interpreted as text/CSI.
- Private mode 7727 (extended keys) silently ignored.
- st.info: add RGB, Smulx, Setulc, kxIN, kxOUT and Hls so tmux and
ncurses apps use truecolor, styled underlines, focus events and links.
