Not to state the obvious but you did find this page right?
https://docs.moodle.org/dev/Availability_conditions
Maybe this is the 'sparse' one you're referring to but I thought it was pretty good. (Disclaimer: I wrote the original version of this page. ;) )
Unfortunately, this system was built back when Moodle used YUI, and it hasn't yet been updated - so the YUI stuff is probably unfamiliar to some developers. Ideally, at some point somebody would update the API (and documentation) to work with the current jQuery/AMD development pattern, but presumably nobody has had time yet...
--sam