The behavior of enrollment has changed significantly between Moodle 1.9 to 2.0 but the documentation hasn't completely been brought up to date and has obvious omissions. The documents need to accurately describe the desired behavior before the code can implement that desired behavior.
2 obvious ones:
1) http://docs.moodle.org/en/Unenrolment Document explains self unenrollments but what about a teacher unenrolling the student?
2) http://docs.moodle.org/en/Enrolments_2.0 This document isnt even close to being complete. Should its contents just be deleted and replaced with a message telling the user to go to http://docs.moodle.org/en/Development:New_enrolments_in_2.0?