bug#20070: 24.3; have commands such as downcase-region act on a rectangle region

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Date: Sun, 15 Mar 2015 22:34:02 +0200
> Cc: Pål Grønås Drange
>       <paal.drange@gmail.com>, 20070@debbugs.gnu.org
> 
> > Indeed, same problem as kill-region, to which I had to add a `region'
> > argument (which basically says "we're called interactively so use
> > whatever is the region rather than BEG and END").
> 
> Then maybe support for the rectangular region should be introduced
> to every command by adding a new argument `region' with a list of pairs
> ((BEG1 . END1) (BEG2 . END2) ...) and keeping the existing arguments
> BEG and END unchanged?

What are BEG1, END1, BEG2, END2, etc. values here?  In what units are
they measured?  Are they pixels, are they columns, something else?