RegExp Adaptive mode with Help

This plugin is one of the 2 question behaviours to be used exclusively with the regexp question type. Those behaviours enable you to take advantage of the *Help* feature, which allows the student to “buy” a letter.
Selecting a mode other than None will display a button to enable the student to get the next letter or word (including the very first letter or word).
In Adaptive mode the button displayed will say “Buy next letter” or “Buy next word” according to the mode selected by the teacher. For setting the “cost” of buying a letter or word, see the Penalty for incorrect tries and Buying a letter or word settings further down the Edit form.