Use standard error message formatting. Otherwise
# apt-config dump
E: Syntax error /etc/apt/apt.conf.d/10jidanni:11: some problem...
Can't be parsed by important editors. Even validate(1) has
--[no]emacs
(don't) use an output format intended for parsing by (X)Emacs,
autodetected.
With standard error formatting, one can jump to the problem line in
one keystroke.
What a relief! Finally, a good suggestion. My inbox is backed up.