Save before playing

It would be good if it's an autosave every X minutes, or after every action. (Obviously not overwriting the manual saves, as you may wish to play without saving). Sometimes you may make a number of edits without hitting play, so hitting play might not be the best action for the save.

That gets extremely complex, Tim.

Autosave after every action could potentially slow down the UI. Unless the autosave after every action wrote a journal entry. (This has its own problems, but does not need to be a 100% perfect solution.)

Autosave after every X minutes is a good idea. That way a person can control the timing, or disable it.

Autosave on play would, as you point out, need to be an option that can also be disabled. Keeping in mind that it should be enabled by default.

A computer program must never, ever, ever lose (more than a minute or two) of a person's work.

Applied the patch from Andy Finch, and made a few small changes. The autosave seems to work really good, at least during my testing. When the autosave happens, it dims out the save button on the toolbar, which makes this pretty easy to visually see it happen.