This allows the teacher to define what students are supposed to submit
(online text and/or attachment) and if the given submission part is
required or optional.
dirname() is a slow function compared with __DIR__ and using
'/../'. Moodle has a large number of legacy files that are included
each time a page loads and is not able to use an autoloader as it is
functional code. This allows those required includes to perform as
best as possible in this situation.