I dislike this idea. I think for most people, most of the time,
the lines acme's working with will fit well within the width of
a window. Yeah, I bet most of us have run into longer lines at
times, but the interface is optimized for the common case. I
wouldn't like to see that go.

Having the "undo" (paralleling the "undo" of a 1-2, 1-3 chord)
is very nice. The feature is certainly *not* "useless" for not
being 100% reliable; what's it' off by, a line? Even that's a
"good enough" job for your eye to find the line quick enough.
Anthony