mtext_get_prop_keys(3m17n) on Linux
The text 8e390b69b8f6, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.
Get a list of text property keys at a position of an M-text.