Question requiring at leat one correct (instead of all correct)

[blaiseli]

I haven't seen this request, but maybe I didn't look carefully enough: I tried to make a question where several answers are considered correct, and the behaviour I obtained was that the only correct solution was to check all correct answers. My intention was that it would be considered correct if at least one of the correct answers was checked (and none of the wrong answers).

For instance:

question("Select at least one TRUE expression",
         answer("`2 < 4`", correct = TRUE, message = "`!FALSE` is also correct"),
         answer("`!FALSE`", correct = TRUE, message = "`2 < 4` is also correct"),
         answer("`TRUE & (2 < 1)`"),
         allow_retry = TRUE
         )

Selecting only one of the correct answers is considered wrong. What would be nice is an any_correct option that would result in the desired behaviour.

A related feature would be to allow multiple choice square check boxes even when only one answer is correct, in order to avoid giving the hint that only one answer is correct.