WYSIWYG or RTE input box logic

Hi guys, I need for a site I'm developing a RTE also called WYSIWYG input box, like this one here at WWF, however, I would prefer to build one myself, but don't know where to start realy. I quickly looked at the code that makes this one work, and a few questions poped up immediatly, such as:

1. What's with this [frames.message.document.designMode = 'On']? Could it be that RTEs are only possible with Javascript?

2. WWF RTE uses a BODY inside an IFRAME written with an ASP ... .Write and inside it with a JS [document.write] ???? WTH ?

Any pointers please, I need to write this myself as adapting from other solutions will be more trouble than anything else, once I know the logic behing this I manage my way from there.

Thx guys.

Thx, will follow that to see if it is not a IE only type of thing, anyway, I found a great 100% free RTE that on first looks is easy to digest and adapt, anyone interested head over here >>>>>>>

Theres even an ASP demo and it only requires 3 files the main one, a JS and a CSS, great, ahh, and the little images of course.

I will still try to build my simple RTE as I enjoy the challenge, but if not possible, I'll use the free one.

Thx.