This is an OS-like feature, and a good one, so it begs to have the same level of functionality you expect from an OS including "undo". When you're editing text you're in a flow and undo is really crucial, not just with spellchecking but just in general. Being able to use undo when typing into a rich text field like the one for this post for example, allows you to treat an HTML field the same way you would a word processor, but without it typing anything longer than a couple of words feels pretty primitive.
Perhaps you could build in some standard undo functionality into TextField or whatever part of the API this spellchecker resides in, then provide a switch to turn it on or off, or set number of undo levels. It would be a great overall addition to Flash's capabilities.
Great job with the spellcheck feature so far, thanks for adding it!
Undo is a feature that's built into the Text Layout Framework. When there's a version of Squiggly for TLF, undo and spell check will both be available.
In the mean time, Jacob Wright has written a library that adds undo/redo functionality to text fields in an application. You could use that in combination with Squiggly, since they both work with text fields based on the "classic" TextField class.
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