Compare:
https://docs.python.org/3.6/library/asyncio-sync.html#asyncio.Lock
https://docs.python.org/3.8/library/asyncio-sync.html#asyncio.Lock

First version is much more detailed.
It allows to avoid confusions like one with unlocking order:
https://stackoverflow.com/q/55951233/1113207

Also, the docstring of asyncio.Lock still states:

    When more than one coroutine is blocked in acquire() waiting for
    the state to turn to unlocked, only one coroutine proceeds when a
    release() call resets the state to unlocked; first coroutine which
    is blocked in acquire() is being processed.

Hi hniksic,

Could you add your Github Account to your BPO account, without that, we can't work on your PR, and you need to sign the CLA.

Thank you

How do I connect the accounts?

Please note that I've previously submitted PRs which have been accepted, e.g. https://bugs.python.org/issue34476 and https://bugs.python.org/issue35465

Ok, found it, and I've now updated the github name on my bpo account. I'll gladly sign the CLA if needed, I thought it wasn't necessary for small changes based on previous experience. Please advise whether it's necessary here.

If I read the Licensing section into the devguide, a contributor (me, your, etc..) has to sign the CLA. 

https://devguide.python.org/pullrequest/#cla

"To accept your change we must have your formal approval for distributing your work under the PSF license."

the verb is must -> required!

Thank you

I would say that unblock order is an implementation detail (which is unlikely be changed though).

I'm biased how should we document it.
Yuri, your opinion is very welcome.

@matrixise I've signed the CLA in the meantime, and it's now confirmed by https://check-python-cla.herokuapp.com/

Thanks for the pointer.

Hi Hrvoje Nikšić,

Thank you for the CLA, now, we need the opinion from Yury and their approval, I am not an expert of the asyncio.

Thank you,

New changeset 34f4f5efea730504216ee19f237734e0bb0104ee by Miss Islington (bot) (Hrvoje Nikšić) in branch 'master':
bpo-36794: Document that Lock.acquire is fair. (GH-13082)
https://github.com/python/cpython/commit/34f4f5efea730504216ee19f237734e0bb0104ee

New changeset 4e1e887203ef069bf293ecabd945f7567d6a4879 by Miss Islington (bot) in branch '3.7':
bpo-36794: Document that Lock.acquire is fair. (GH-13082)
https://github.com/python/cpython/commit/4e1e887203ef069bf293ecabd945f7567d6a4879