Perfect, this was a shortcoming of CodeMirror. Thank you for putting this together!

I've implemented it but there seems to be an issue. Most snippets aren't highlighted. Maybe it's a problem with the way it interprets the start and end of scope.

@Hawkee I just updated this to the code I'm using now. It should be mostly the same with a few minor changes.
I'm not sure why it doesn't highlight the same as it did in testing, but maybe try the new code.
Is there a way I could test this and get the same result you do here?

It still doesn't seem to be working. You can view the source of this page to see how I'm calling Codemirror. It's a pretty basic call from a textarea. Do you have a working example online?

Here is a link to a basic example: http://lawnmower.asuscomm.com/codemirror/mode/mIRC/

I think I found the issue. It looks like a case sensitive issue @Hawkee
If I change

CodeMirror.defineMode("mIRC", function() {

to

CodeMirror.defineMode("mirc", function() {

It breaks and doesn't work at all.

So what I've found is that this:

CodeMirror.defineMIME("text/mIRC", "mIRC");

must match this:

CodeMirror.defineMode("mIRC", function() {

The case in the defineMode must be exactly the same as the defineMIME

I also found that the defineMIME should be at the top of the script.
I will update this code now to all lowercase and move the defineMIME to the top

That did it! Thank you. Looks great!

Is that the version of the script from the top here, because I still see an unmatched quote issue that I'm not getting on my tests.
You can see it here: http://www.hawkee.com/snippet/9837/

Note I also found that "text/mIRC" has to match the mode: on the html. I changed it above to "text/mirc" to make it uniform.

Edit I'm pretty sure the site is running an older version, because I see several other glitches that I already fixed.

I updated to the latest version. How is that?

It looks good, but I found another issue. I added support for mult-line comments, as mIRC does support / /
and lots of people use this type of comment. The problem was, there wasn't a check for / inside a function or if statement.
ie. if (/ iswm %bla)
You can see what it does here: http://www.hawkee.com/snippet/9858/
It basically just comments out the rest of the script and it looks pretty stupid.
Anyway @Hawkee , I updated the script and this issue should be fixed.

Good fix.

Cool . It looks good.

Updated Found a typo preventing "writeini" from being highlighted. I had "writeint"
You can see it here: http://www.hawkee.com/snippet/8545/