Actually, the principle of Kix is simple. Compute each letter size,
done. Ok, it is not so easy. For example browsers render various
spaces widths between letters If text align is justified (but
justified text does not fit in web design, so remove justify option is
good workaround).
Caret is blinking div. You also need another hidden div with
contentEditable to allow rich past. The main problem I had with
implementing Kix like editor (I made it several years ago) was that I
had no good library for that task. But that's not true anymore, we
have Closure :) Good luck and dont hesitate to ask me for another
nasty details. Cheers.