I’m extremely fond of rectangle editing (the ability to select a rectangular region and apply editing commands only to it), but I’ve always disliked the fact there was no way to visually highlight the exact rectangle region you’ve currently selected. Let’s delete some text in a rectangular region (with C-x r d), so you can see where the problem lies:

old rectangular selection

It’s not immediately clear where the rectangle bounds are (it’s clear where the rectangle region starts, but it’s not so clear where it ends), which is a source of constant confusion for many people.

Emacs 24.4 finally fixed this with the introduction of rectangle-mark-mode (bound by default to C-x SPC). Let’s see it in action:

new rectangular selection