* Heime <heimeborgia@protonmail.com> [2024-12-03 23:49]:
> Ok, so I look for prog-mode in the major mode file I am interested in.
> 
> I tried again, this time from fortran-mode.  And found 
> 
> (define-derived-mode fortran-mode prog-mode "Fortran"
>  
> So fortran-mode is derived from prog-mode.  Not the other way round, as I
> had thought initially.

You are doing well, keep researching, there are many modes to go:

Click or type M-RET on a completion to select it.
Type M-<down> or M-<up> to move point between completions.

See the attached file, there are many modes.

-- 
Jean Louis