Vague Description / Easy Task - Intermediate Algorithm Challenge - Missing Letters

[Jamayk]

My solution checked all FCC tests and also returned 1 or more letters (if it was the case).
But then I had some more Qs: what if the letters have random order, what if my str contains other chars, and so on; then I checked FCC Wiki:

There is currently no test case for the string missing more than one letter, but if there was one, recursion would be used. Also, the letters are always provided in order so there is no need to sort them.

Clearly I was overthinking it; but maybe description of the challenge should be a bit more accurate, like specify that the str is a-z, sorted, missing only one letter, etc. (like the quote from Wiki)
I also think this exercise is a lot easier than some prev ones, if we keep it only a-z, sorted, 1 letter missing.

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While searching for results/issues on this challenge, I've found #13431; I can fix it if fixtheelvis is busy for now.