I do not fully understand what "short" checkbox is supposed to do.
I think you should add an help description to explain its purpose to user. Documenting it in README could be nice too.
Moreover its edition seems pretty buggy. Steps to reproduce :
Add an activity and set relative date restriction (1 day after user enrolment) with "short" checked.
Edit the activity and uncheck "short" then save.
Edit the activity again
Expected result
"Short" is unchecked
Actual result
Short is checked
The idea to implement a short field to control the way the restriction is described (related to the $full parameter of the get_description function) was abandoned.
I do not fully understand what "short" checkbox is supposed to do. I think you should add an help description to explain its purpose to user. Documenting it in README could be nice too. Moreover its edition seems pretty buggy. Steps to reproduce :
Expected result "Short" is unchecked Actual result Short is checked
Tested on 3.7.1+ (Build: 20190725)