DOC: document optional arguments on plot submethods
- [x] closes #11042 
- [ ] passes `black pandas`
- [ ] Signatures and doc strings for plot sub-methods opt-args added.

Is there an issue for this? > Is there an issue for this

#11042 @hancar can you fix up merge conflicts and address comment above? > @hancar can you fix up merge conflicts and address comment above?

Oh, thank you for reminding, today I will find some time. Hello @hancar! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:

* In the file [`pandas/plotting/_core.py`](https://github.com/pandas-dev/pandas/blob/002fc51536147df6d2b2361b6fec95eba9af4ca2/pandas/plotting/_core.py):

> [Line 1336:89](https://github.com/pandas-dev/pandas/blob/002fc51536147df6d2b2361b6fec95eba9af4ca2/pandas/plotting/_core.py#L1336): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (89 > 88 characters)
> [Line 1558:89](https://github.com/pandas-dev/pandas/blob/002fc51536147df6d2b2361b6fec95eba9af4ca2/pandas/plotting/_core.py#L1558): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (89 > 88 characters)



##### Comment last updated at 2019-11-19 08:22:52 UTC Seems like some test and code checks are failing. Let us know if you need help looking into them. > Seems like some test and code checks are failing. Let us know if you need help looking into them.

Yes please, now I would really appreciate some help. It seems like the tests fail on some linting or docstring validation, but I didn't manage to rerun the tests locally to find the problem. This is from `Checks/12_Testing docstring validation script.txt` in the logs:

```
2019-10-10T22:31:39.8687326Z scripts/tests/test_validate_docstrings.py ..............................................x..x..............................................docstring1: err desc
2019-10-10T22:31:39.8688602Z docstring1: err desc
2019-10-10T22:31:39.8689131Z docstring1: err desc
2019-10-10T22:31:39.8689537Z docstring2: err desc
2019-10-10T22:31:39.8689947Z docstring2: err desc
2019-10-10T22:31:39.8717964Z ..EXECUTED
2019-10-10T22:31:39.8732189Z {"docstring1": {"errors": [["ER01", "err desc"], ["ER02", "err desc"], ["ER03", "err desc"]]}, "docstring2": {"errors": [["ER04", "err desc"], ["ER05", "err desc"]]}}.Series.foo: err desc
2019-10-10T22:31:39.8732941Z DataFrame.bar: err desc
2019-10-10T22:31:39.8733428Z Series.foobar: err desc
2019-10-10T22:31:39.8733849Z Series.foo: err desc
2019-10-10T22:31:39.8746350Z .
```
Can you give me some hint, please? Thanks for the PR @hancar - mind merging master and addressing @WillAyd comments whenever you have time- thanks! @hancar looks like some CI issues can you take a look? Closing as stale, @hancar if you want to finish this, please let us know to reopen.