Customizing the mode line

[Eli Zaretskii <eliz@gnu.org>]

Do we have some convenient UI for customizing the mode line?  The user
manual doesn't mention any.

I frequently find myself in a situation where the information that's
important to me is pushed beyond the right edge of the mode line, and
is thus invisible.  Annoyingly, a large part of the real estate of the
mode line is taken by information that is much less important, like
the percentage of the file before the window start and the list of
minor modes in effect.  The latter, for example, is quite static in
any given buffer, so once you saw it for the first time, there's no
need to continue showing it in such a central place.  However, even in
a C buffer, the mode shown is "C/l Abbrev", which is quite long.  And
when I read mail, I see something like "RMAIL XXXX/YYYY answered,
deleted"; when replying to mail it's "Mail Fly Abbrev Fill", etc.
These are very long strings that I don't need to see all the time,
because they almost never change.  But they steal too much precious
space.

By contrast, dynamic information such as the current time, the system
load, the battery condition, the mail indicator, the current function
(when in which-func-mode), etc. -- these are banished off the edge of
the mode line, and cannot be consulted.  This effectively makes these
features unavailable, unless one is willing to make her frames
unreasonably wide or even full-screen.

I consider this a bad misfeature.  What's more, modifying what's in
the mode line is not an easy task (unless I'm missing something): it
boils down to reading bindings.el and manually setting various parts
of standard-mode-line-* variables to remove or rearrange what is
shown.

Can we make the mode line display more ergonomic, or at least more
customizable?  Should I file a "wish-list" bug for this?