RE: Dired: Improve symmetry in mark/unmark commands bound to keys

[Drew Adams <drew.adams@oracle.com>]

> > I) Add optional argument in 6) unflag-p to behave as the others.
> > II) Add a new command `dired-mark-or-unmark-extension', as
> > `dired-mark-extension' but, in interactive calls:
> > * A prefix argument _unmark_ files.
> > I propose to rebind '* .' to this command instead of the
> > `dired-mark-extension'.
> > After I) and II) we have an uniform behaviour for all
> > commands marking files which are bound to keys.  Powerful and easy
> > to remember.
> 
> I'm okay with that proposal, but please leave the "* ." key sequence
> at its present binding.  For the new dired-mark-or-unmark-extension
> command, I can propose "* e" or "* x", which are not yet taken, both
> of them mnemonically resembling "EXtension".

FWIW, I favor Tino's proposal, including having `* .' UNmark
with a prefix arg (just like the other `*' commands).

I see no special reason why a prefix arg to `* .' would read
the character to use for marking, instead of having it unmark
as proposed.

(FWIW, In Dired+ `* .' has long been bound to a command that
does what Tino proposes.  I've never heard a complaint.)

A prefix arg for `* .' currently is not useful, IMO, and
likely never used.  It marks the files using a character that
you specify.

Instead, users can use `* c' to change the mark character for
the marked files, however they were marked - very useful.

The ability to have a different mark character has nothing
special to do with marking files by their extension.  There
are lots of uses of different mark chars.  I've never heard
of _anyone_ taking advantage of the vanilla `* .' prefix arg
behavior to use a different mark character while marking a
given extension.

In fact, my impression is that there are very few Emacs users
who even know about `* c', or know that you can have different
marks and how you can put them to use.  See this bug thread,
for example: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=21746#8