DOC: pandas.Series.str.isspace has wrong documentation
#### Location of the documentation

[pandas.Series.str.isspace](https://pandas.pydata.org/docs/dev/reference/api/pandas.Series.str.isspace.html)

#### Documentation problem

> Check whether all characters in each string are alphanumeric.
>
> This is equivalent to running the Python string method str.isalnum() for each element of the Series/Index. If a string has zero characters, False is returned for that check. Seems like it was somehow copied from `pandas.Series.str.isalnum`.


That does not seem to match the function.

#### Suggested fix for documentation

Not copy the doc of `pandas.Series.str.isalnum` but rather provide a specific one.
