DOC: default axis is unspecified for DataFrame (and even some Series) operations

[toobaz]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.max.html

Documentation problem

The docs for pd.DataFrame.max() state, about the axis argument:

axis{index (0), columns (1)}

    Axis for the function to be applied on.

The docs for pd.DataFrame.std() don't even include the explanatory sentence.

Instead, the docs for pd.DataFrame.cummin() have

axis{0 or ‘index’, 1 or ‘columns’}, default 0

    The index or the name of the axis. 0 is equivalent to None or ‘index’.

... which I think is good (also notice the more understandable explanation of the equivalence between numbers and descriptions), except that the default in the signature is None, not 0, and that I would replace the last sentence with None is equivalent to 0 or index.

Suggested fix for documentation

Simplest solution: specify, in all these signatures, that default: None and that None corresponds to 0 (see above for cummin()).

My preferred solution, set the default to 0 (rather than None), specify that default 0, start deprecating None (which is likely not used anywhere anyway). But given that the current max() signature states axis=NoDefault.no_default, which I don't know the meaning of, maybe there is something I am missing? Still, the signature for std() looks similar except that axis=None (the axis docs still provide no default), and conceptually the kind of requested data manipulation is similar...

[toobaz]

I'm happy to provide a PR once we pick the preferred solution.