Actually, there are two: NASM-IDE, which is yet another Turbo Pascal 4.0 clone like RHIDE, and NasmEdit, which is a rather simple(-minded) but workable editor written in Java. I was using NasmEdit for a while, but lately I've mostly just using Emacs, with Notepad (under Windows) or Pico (during the few times I'm running Linux, lately) for small jobs.
However, I firmly believe that th more different approaches there are, the better everyone's choices can be. Writing a new IDE, if it is not just a clone of any existing system, would be an admirable thing.
As for the highlighting issue, can you be a bit more specific about the system you've designed? Is it text mode (as I am assuming) or graphical? What text or graphics mode(s) is it ideisgned to work in? If it is text mode, are you writing directly to the screen buffer, or using some sort of curses-esque text-manipulation library? In what manner do you wish the text to be highlighted?
On the general issue of editor design, you may wish to consult an excellent volume on the subject,
The Craft of Text Editing by Craig Finseth. The original book may be found at most university libraries, and the entire text is available on the web site and may be downloaded. While he uses many examples derived from Emacs - the book is subtitled is "Emacs for the Modern World" - this is primarily because it was among the first general full-screen editors, and it's internals are widely studied and well-known. The book applies to editing in general, and is very easy to follow. It's major flaw is it's age - it concentrates a lot on efficiency issues that are less important than they were on a 68030-based workstation with 2M of free memory (don't get me wrong - efficiency is at least as important today as it was then - but the particular optimization issues are not necessarily the same). While the version on the web site is more recent, it does not appear to be seriously updated. Finseth's code is also a bit clumsy in places, but this is not a serious hinderance.
This is yet another book I would recommend to nearly any programmer, especially anyone doing OS development, as most OS writers at some stage in their work will need to write an editor of some kind, even a very simple one. The sections on buffer handling and on screen refreshing are particularly illuminating.
