DOC: pivot function
In docs [DataFrame.pivot](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.pivot.html) is a bit unclear, what means **object**:

>index : string or **object**, optional

>Column name to use to make new frame’s index. If None, uses existing index.

>columns : string or **object**

>Column name to use to make new frame’s columns

>values : string or **object**, optional

Is it `Multiindex` ? Or `None` ? Or `Series`?

[SO question](https://stackoverflow.com/q/44314003/2901002)