>> >> > Then its possible options for such hook could include:
>> >> >
>> >> > - xdg-open-function
>> >> > - mailcap-function that adds mailcap candidates
>> >> > - dired-x-guess that adds existing dired-guess-shell-alist-default
>> >> > - Windows-specific candidates from w32-shell-execute
>> >> > - etc.
>> >>
>> >> Here is the implementation:
>> >
>> > Thanks, but please don't put this stuff in simple.el.  There's no
>> > reason to have this preloaded in Emacs.
>>
>> I can't find other place to put these 50 lines.  I added to simple.el
>> near read-shell-command because it's used by read-shell-command.
>
> IMO, read-shell-command should not by default call these helpers.

It doesn't call them by default.

> If we cannot find a suitable non-preloaded file to put this stuff (is
> subr-x.el okay, for example?), it's okay to start a new file.

Ok, then let's add this to dired-aux.el since it's used in dired.

>> Also shell-command-guess is used by dired-read-shell-command
>> ('!' and '&' on a file in dired).
>
> Likewise here: users should by default be able to invoke these Dired
> commands without automatically loading those helpers, which come with
> quite tangible ballast.  For Dired, this is perhaps less important,
> since Dired itself is an optional package, but still: I think it's
> wrong to do this by default.

Ok, I removed mailcap and xdg from defaults: