Thanks Jim (@_jims),
I have another use of Prompt With List where it's the actual initial character that I type, and even if the character appears elsewhere, if it's the first character, it's sufficient. In this list:
I can type r, s, e, t, m, or a and even though all of those letters appear in Keyboard Maestro, the choice will be executed as I desire.
I suspect the problem is the fact that in this test case it is not the initial character. That's what I was testing and it looks like it doesn't work as I had hoped.
It appears that there's a two-step process (which I recall, possibly, being explained somewhere but it's not in the User Manual and I couldn't find it elsewhere) where if there is a match to the initial character, that takes precedence, and when that option is eliminated, then it's a search for matches anywhere in the prompt string. It does not, as I was presuming, keep searching from the front, it only does that to disambiguate IF there is a match of initial characters. It's an either or, starting at the first character or otherwise starting anywhere in the string.
Perhaps if I could somehow "front load" the search string to start with the "[", where a keyboard character would follow that, rather than replace it, then I could make that choice in a single keystroke. I tried setting "[" to be the "default" and it appeared in the search field, but I had to type a Right Arrow to keep it there so that I could then type the letter choice, and that isn't what I want.
Or perhaps I could use the technique in The “Follow Menu Choice with Return” Macro (v0.5) and instead of having the single-key macro send a character and a Return, it could send three or four characters.
In any case, it looks like my test demonstrated how "Prompt With List" actually works, and it's not the way I was hoping for at first.
Thanks.