preferred method for coexistence of debconf- and manual parts in conffiles?

[frank@kuesterei.ch (Frank Küster)]

Hi,

if a package wants to use debconf to manage a configuration file, but
still let the user have the option to manually add entries - is there a
preferred way how to do this?

The packages I have on my system (mostly woody, however) don't care at
all about this and simply say "don't edit this file", except one:
localeconf. However, there's a bug associated with that behavior,
172439 - but to be exactly the bug is about bad cooperation between
localeconf and locales, not about the concept itself.

Besides that, the localeconf method seems very good to me:

Put the information from the debconf database into the file, but between
markers ### begin DEBCONF section for $package...  ### end DEBCONF
section for $package. So an admin can add his customization before or
after that, and upon dpkg-reconfigure or an upgrade only the part
between the markers will be changed. 

Is this concept o.k.? I couldn't find anything in the policy about that.

Here's why I come to ask the question: Recently, a bug was filed against
tetex-bin, #209395, criticizing that a configuration file, language.dat,
is not in /etc, but under /var. The reason why it was put there was that
it was a generated file: Not user-editable, the only way was to run
dpkg-reconfigure. A user that wants his own, manually edited file can
still create it under /etc and divert the link that now points from
/usr/share/texmf/tex/generic/config/language.dat to
/var/lib/texmf/language.dat, so that it will point to his own file. He
should have answered "no" to the question wether debconf should manage
this file if he wants to do that. But it's not necessary for his setup
to work - until he accidently accepts a change debconf proposes upon
upgrade and wonders why it has no effect...

The problem with that is, as pointed out in the bug report, is that now
both the debconf database and language.dat are under /var, where backups
are rarely done on homeusers systems, and he wants it under
/etc.

I would prefer it to be under /etc also because it _is_ a configuration
file, and thus it belongs there. But to preserve the possibility of
local additions, I would like to find a way for co-existence of
debconf-managed and manually-edited parts.

TIA, Frank
-- 
Frank Küster, Biozentrum der Univ. Basel
Abt. Biophysikalische Chemie