Re: buffer-substring-filter

[Richard Stallman]

This is a clean implementation of the feature I had in mind.
Using mapcar is a little wasteful, since it makes a list of the results
only to throw them all away.  Better to use dolist.

It would be good to move point to BEG, temporarily,
so that the functions can tell where the text came from
in case they care.

However, the real question is whether this is the right feature
for doing the job.  Have you changed longlines.el to use it?
Does it do what longlines needs?

I think that some other functions would need to use this feature.
One is append-to-buffer.  Also the rectangle functions should use it.
Maybe other places too.