A opportunity raised by /undo

[davewsmith]

If you haven't covered it elsewhere in the book, there's a "sometimes the the need for a re-design comes up during implementation, and that's entirely normal" opportunity in this chapter. Sometimes ongoing development nudges one towards the need for new internal APIs. Recognizing how a clean API can simplify ongoing development is common on 'real' programming. Acting on that can lead to more habitable programs.

Here, as Actions get more interesting, especially when considering why the Entire key would require special Action rather than just being another char to insert, one might pause and consider that a large part of the complication in new Actions is that way the text under edit is represented isn't behind a clean API -- one that hides whether the internal representation is a string, an array of line strings, or a more sophisticated gap buffer.