Hi, I'm a new contributor trying to get started with documentation and testing.

I have been following and testing PEP525 and PEP530 and feel familiar enough to try to work on adding this to the Python Language Reference if it would not be redundant with work already being completed. I think this makes sense to tackle along with issue 28090 as it appears that documentation of asynchronous generator expressions would necessarily refer to terminology from asynchronous generator objects. 

Specifically, for PEP525:

async generator functions would be added first in section 3.2 after coroutines.

Most of the work would be in expanding 6.2.9 (yield expressions) to discuss the asynchronous case, probably adding 6.2.9.3(4) to document the methods for asynchronous generator objects.

In section 8.8.1 I would need to remove the statement “it is a syntax error to use yield expressions in async def coroutines”, add statement that “yield from” is a syntax error in this context.

Finally, the new concepts should be added to the Glossary.

Then for PEP530:

Section 6.2.4 (Displays for Lists,...) needs to be updated for the grammar change that adds the optional ASYNC, i.e.:

comp_for: [ASYNC] 'for' exprlist 'in' or_test [comp_iter]

Then both sections 6.2.4 and 6.2.8  (Generator expressions) need to be expanded to include the async case.

If writing this up is not already underway, and if I’m generally on the right track for what needs to be done, I think I can have a reasonable patch for this by the end of the week. Also, please feel free to contact me if there is any other documentation/testing/test coverage work that I could help with. The new native coroutines are an area of particular interest for me.