bug#1305: All code that currently beeps should use visual bell instead

[Gregory Heytings]

> > > I think, perhaps, introducing a new visible bell (across all 
> > > significant system), that's considerably less intrusive than the ones 
> > > we have today on GNU/Linux and Macos, might be an option.  And then 
> > > defaulting to using that.
> > >
> > > Gregory suggested blinking the cursor in a different colour -- 
> > > perhaps?
> >
> > I attach a POC of what I have in mind.
>
> If this is being proposed as the default setting, then we should have a 
> different default for TTY frames, because AFAIR cursor color cannot be 
> changed there, right?

Indeed.

> >   (sit-for 0.5)
>
> I think half a second is too long, a bell should be much shorter, like 
> 0.1 sec or something.

Hmmm... 0.5 seconds is the duration of typical audible bells.  And with a 
sit-for, it's at most 0.5 seconds, when the user presses a key the bell 
signal disappears.  That being said, I agree with you that 0.5 seconds is 
perhaps a bit too long, so I changed it to 0.25 seconds.

I attach the updated POC, which works on non-graphical displays.

visible-bell.el
Description: Text document