XmTextGetSubstring(3) on Linux
The text 158d36a47a0c, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A Text function that retrieves a copy of a portion of the internal text buffer "XmTextGetSubstring" "Text functions" "XmTextGetSubstring"