It was possible before new question engine to have abstract question type (there even used to be one for calculated question) that doesn't used to create question, but to inherit other question types/questions from.
Is it still possible in Moodle 2.1 with it's new question engine and how it is achieved?
What Jamie Pratt has done is to base one question type on another https://github.com/jamiepratt/moodle-qtype_ddwtos/blob/master/question.php#L38
Where he has wanted an abstract base class, he has chosen one question type, and put the files in there. For example: https://github.com/jamiepratt/moodle-qtype_gapselect
This seems to work quite well.
