I'm afraid that safari definitely doesn't act in the same way as IE in designMode. I wish it did! In fact, as far as I can work out, safari really doesn't implement a lot of the functions that either IE or Mozilla do to support designMode features. For example: getSelection in safari returns selected text, rather than an HTML object, which is what is often needed when developing, for example, a WYSIWYG editor ;)

If anybody believes this to be different, and has the documentation to back it up, I would really really appreciate someone letting me know ;)

Until then, if you want your WYSIWYG editor to work on OS X, just install FireFox on your Mac. It works fine.