Based on the discussion here, I've updated the ticket with the following changes (text copied from the ticket):

Now called 'MULTIRESPONSE'.

Horizontal and shuffled options added (MULTIRESPONSE_H, MULTIRESPONSE_S, MULTIRESPONSE_HS).

Positive fractions (whereby '=' is treated as 100%) are scaled so that the combined total of all positive fractions is 100% (nothing happens if they already add up to 100%).

If no fractions are specified at all, then all incorrect answers are given a fixed score of -50% (to avoid having to use fractions at all in the most simple version of the question), if any fractions are specified (either positive or negative), then incorrect answers will need to be manually given a negative score.

For clarity, a couple of examples:

Please select the fruits {1:MULTIRESPONSE:=Apple~Burger~Hot dog~Pizza~=Orange~=Banana} and vegetables {1:MULTIRESPONSE_HS:%10%Raddish#Good~%-20%Chocolate~%-30%Biscuit~%-10%Cheese~=Carrot}

This translates into:

- Multichoice, multiple answer, unshuffled, vertical checkboxes
- Apple +33.3% (scaled so all +ve answers add up to 100%)
- Burger -50% (automatic negative score for answers not marked as correct)
- Hot dog -50%
- Pizza -50%
- Orange +33.3%
- Banana +33.3%

- Multichoice, multiple answer, shuffled, horizontal checkboxes
- Raddish +9.1% (correct answers of +10% and +100% scaled to 9% + 91%, to add up to 100%)
- Chocolate -20%
- Biscuit -30%
- Cheese -10%
- Carrot +90.9%

So, the simple version, where no percentages are specified, works as expected - i.e. select all (and only) right answers = full marks, any wrong answers result in less than full marks. At the same time, the teacher still has the option of manually specifying percentages, at which point they have the flexibility of specifying the exact negative marks for incorrect answers (including the option of specifying a mark of 0 for any answer).

Further feedback (especially from trying out the question type) would be appreciated.