bug#22873: Can we support multiple cursors?

[Eli Zaretskii]

> Date:  Sun, 13 Aug 2017 20:20:10 -0700
> From:  Keith David Bershatsky <esq@lawlist.com>
> Cc:  22873@debbugs.gnu.org,John Wiegley <jwiegley@gmail.com>,Marcin Borkowski 
> <mbork@mbork.pl>,Richard Stallman <rms@gnu.org>
> 
> I read through the comments in xdisp.c that immediately precede move_it_to 
> and I also looked at all of it uses within xdisp.c, but I am still unclear 
> how to limit move_it_to the it.last_visible_y.

Like this:

 move_it_to (&it, POS, -1, it.last_visible_y - 1, -1, MOVE_TO_POS | MOVE_TO_Y);

where POS is the buffer position.  You can find many examples of this
in xdisp.c.

> I got the impression that if I put it.last_visible_y as an argument of 
> move_it_to, that `it` would move to that location instead of POS if POS 
> cannot be found.

It stops when the first condition is satisfied.  If it reaches POS
before the window end, it stops there; otherwise it stops at the
window end.  It is then a simple matter of testing IT_CHARPOS(&it)
against POS to see which of these conditions caused it to stop.