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

[Drew Adams]

> > Moving???  Why do you think this would be better
> > than simply blinking the echo area?
> 
> "Blinking" is also movement. I don't have a specific
> animation in mind.

"Blinking" is the "animation" provided by
`echo-bell-mode' (you asked for that): the echo
area is briefly highlighted with a different
background.

Users can easily control the duration of this
"flash", as well as its color.  And they can
control what text, if any, is shown at the right
edge of the area.  The default text is musical
note chars.

Different behavior & appearance are appreciated
differently by different users.  One user's
valued indication is another's annoyance.  This
simple mode lets you easily have no indication
(mode off) or any degree of interruption you
might want.