Sometimes, not always, this is the only reasonable documentation that can be written,
If throbTheWangle is a good name, perhaps a self-explanatory name, for a function, then there's little more to say about it. It may be very easy to understand in the context of the complete API, and other documentation. However you can't not document it. That would invite understandable criticism.
There are other circumstances where there's lots more to say, and in that case the documentation should be more expansive.
An API can quite easily, and reasonably, span both extremes. The documentation should say as little or as much as is needed about a particular API, and not feel compelled to conform to inappropriate conventions.
2. AES-256 is slower than AES-128, but actually slightly weaker. Why, specifically, was AES-256 chosen? 3. What cipher modes are used, and where? I skimmed the site briefly but though some other details were disclosed,
From the API documentation (at https://mega.co.nz/#developers):
"All symmetric cryptographic operations are based on AES-128. It operates in cipher block chaining mode for the file and folder attribute blocks and in counter mode for the actual file data."
Of course their own client may work differently.
"Well, it don't make the sun shine, but at least it don't deepen the shit." -- Straiter Empy, in _Riddley_Walker_ by Russell Hoban