Re: Highlighting rectangles?

[Richard Stallman]

      Of course, Emacs' region can't do that
    right now and the function that use the region wouldn't know
    how to deal with it, but one way we could do it (I thought at the time)
    is that when we have such a non-contiguous region applied to a function
    whose interactive spec says `r' is to call the function repeatedly
    on the various contiguous subparts of the region.

I guess call-interactively could do this.
It will get the right results for many functions.
But it will be wrong for some.  Consider prepend-to-buffer:
if it operates on the subregions in order from top to bottom,
the effect will be to reverse their order in the destination buffer.

So there has to be another way for a command to specify that it wants
to be called once, with full info on the discontinuous region, so it
can handle all the parts in one go.