This is a means of editing objects manually within the browser. While the browser is in this state, editable elements acquire a UI for modification by means of the enter key. When the designMode property is set to "on" you cannot execute scripts.
The following values can be assigned to this property:
Whether this works may depend on platform and browser versions. It does not appear to be functional on MSIE for Macintosh despite the Microsoft documentation saying that it should work.