RE: Design of commands operating on rectangular regions

[Drew Adams]

> > In order to follow all of this, especially since you now
> > seem to be talking about user-level changes, could someone
> > please specify (describe) the non-contiguous region feature,
> > including how users can create and modify such a region
> > interactively?

Thanks for describing it.  I don't want to belabor this,
but if you have the time, here are some questions.  If not,
I'll see it when I use it. ;-)

> First you can select the non-contiguous region with
> 'C-x SPC', then extend it with the usual point motion keys,

A non-contiguous region with N pieces has 2*N ends.  Which
end(s) get extended with the motion keys?  And does `C-x SPC'
do what it does now, i.e., set a mark at point, so that point
is one end of at least one of the pieces?

Can the pieces (zones) overlap?

> then run one of the commands supporting such regions, e.g.
> 'C-x C-l' to downcase, 'M-%' to replace occurrences, 'C-u M-|'
> to replace the region with the command output.
> 
> > And could you specify clearly the relation between this
> > non-contiguous region feature and rectangles?  Presumably
> > the former is more general but also allows some handling
> > of rectangles (?).
> 
> Rectangles are a subset of non-contiguous regions that can be
> expanded with other shapes, e.g. circular regions.

OK, so I guess from another post by you that the non-contig
region info includes two properties/components: (1) a shape,
specifying, e.g., whether the zones form one or more
rectangles (or circles or whatever) and (2) the zone limits.

Is that right?