Convert rich-text fields to a contentEditable / designMode -based system

[GoogleCodeExporter]

The current regex syntax and match highlighting system of using <pre>
elements underneath <textarea> elements to contain the highlighting (paired
with a container whose scrollbars are used for seemless scrolling) is very
fast but unfortunately too brittle / quirky / buggy to work well across all
A-grade browsers. A more traditional contentEditable / designMode -based
highlighting system might be a pain to set up and will almost certainly be
slower, but it would be more flexible and help to get rid of several
lingering bugs.

Original issue reported on code.google.com by [email protected] on 25 Dec 2007 at 5:22