It means it is a WYSIWYG editor that attaches to a "single content editable element" such as a div. There is then a set of editor states (user typed hello, user

It means it is a WYSIWYG editor that attaches to a "single content editable element" such as a div. There is then a set of editor states (user typed hello, user backspaced 2 so now it says hel, user typed p it now says help. I mean it's pretty easy to understand wording if you are a developer.