A question popped up today as to whether it is possible to accept a decimal answer without a leading digit. As far as I can see, Numbas does not accept the likes of .1 either as a number entry or mathematical expression although it doesn't mark it wrong, just does not accept it. The discussion here has two schools of thought (I'm in the first!)
Writing a decimal without a leading digit before the decimal point is not normal and the students should know better (especially once the system tells them it isn't accepted).
The students may do this anyway and it isn't wrong as such in terms of numerical value.