In a previous post that I posted here, I got responses that contentEditable and designMode are bad practices. So I switched to TinyMCE, but that uses designMode as well... is there something bad about it?
Im using it for a Rich Text editor on my website fyi.
They were trying to tell you not to re-invent the wheel.
If you're using designMode, you probably want either a rich text editor (with toolbars) or a syntax-highlighting code editor.
In either case, you should reuse existing libraries rather than re-creating them from scratch. (Rich text editors are hard, especially across browsers)