addftinfo(1) on Linux
The text e317c22592df, as Debian 10 (Buster) shipped it.
add information to troff font files for use with groff
Flags it lists
-
-asc-height -
-body-depth -
-body-height -
-cap-height -
-comma-depth -
-desc-depth -
-fig-height -
-x-height