Thank you for the advice Neilo - much appreciated.
Ray/Jason - could you confirm whether I would need to re-apply the behaviours again, it's a pretty complicated CMS I've created so I really don't want to mess things up. Also, is it possible to have and use both HTML Editor 2 and HTML Editor 3 installed at the same time so I could continue to use v2 for sites I'd already written and use the new version in the future?