bug#38013: [PATCH] Rectangular region selection with mouse

[Eli Zaretskii <eliz@gnu.org>]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Sat, 9 Nov 2019 20:32:46 +0100
> Cc: rudalics@gmx.at, 38013@debbugs.gnu.org
> 
> In the first patch, the start and end corners of the rectangle had to be a point in the buffer; ie, not a position beyond the end of a line or in the middle of a tab character. That was not only unnecessarily restrictive but also made the rectangle flutter back and forth as the dragged corner passed through lines of different length. Now the rectangle corners can be any character cell.

OK, that's good.

> If that was not the reason for your concern, would you mind describing the problem more in detail and how to reproduce it? 

I still see a 1-pixel thin "region" sometimes, which causes the text
to move horizontally.  More importantly, if I drag the mouse through a
TAB, it moves in jumps of several columns, not one column at a time.