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

[Gregory Heytings]

> 'match' for purposes other than matching?

Why not?  That would be only a default value, to call the user's attention 
that the reason of the error is displayed there.  IMO using yellow for 
that purpose is much better than green (highlight face).

> And speaking of 'error', seeing red is most likely more obtrusive than 
> the current GNU/Linux behavior.

Do you really mean that seeing the cursor becoming red during 0.25 seconds 
is obtrusive?

The current GNU/Linux default behavior is (for those who use Gnome or KDE 
and have not disabled the system bell) to ring the system bell (typically 
during 0.5 seconds).  That's IMO far more obtrusive (in particular for 
your colleagues!) than seeing the cursor becoming red and the echo area 
flashing during a fourth of a second.

> The huge exclamation icon, is that the one? Looks too much indeed.

Yes, that's the one.  And yes, that's too much.