Numerical questions currently have the following behaviour: If someone enters an answer that is not a number, the answer is graded as incorrect.
Thus, for example, if the correct answer is "0.25" and the student enters "1/4", or if the correct answer is "2" and the student enters "two", this is counted as incorrect, and a penalty applied.
On the other hand, if a teacher tries to enter "two" as an (incorrect) answer in the question editing screen, in order to provide feedback, this input is rejected by the form validation code: "The answer must be a number."
I was discussing with Gustav Delius and we weren't sure whether this is a bug or a feature. (An alternative behaviour would be to reject non-numeric answers without penalty.)
Can anyone shed light on this issue?