XmMainWindowSep1(3) on Linux
The text 11e5d18dd186, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A MainWindow function that returns the widget ID of the first Separator "XmMainWindowSep1" "MainWindow functions" "XmMainWindowSep1"