The entire editor is itself written in elisp, which makes it very easy to seamlessly customize it. And customizing editors is one of my most favorite past-times. Don't ask me why, but I've always been fascinated by text editors. I have the documentation for it still, somewhere, as well as the print-out of my editor. So on these pages you'll find out some things that I've discovered either on my own or through the generosity of others on email lists and newsgroups all over the world.
Most modern editors can handle that without too much trouble.
It's presented merely as a way to show that my editor is better than yours. Small Emacs package that changes the cursor from a block to a bar. In overwrite-mode, it changes back to a block. Optionally, it allows the user to specify a name that all such buffers will have, regardless of the directory they point to. There are other packages out there that do similar things, including some things in JDE, but I like this one.