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

[Stefan Kangas]

Gregory Heytings <gregory@heytings.org> writes:

>> '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).

I would propose using a dedicated face for this purpose.