`Dataframe.sample()` isn't validating `frac`
Minor/trivial bug:

https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L4960

Shouldn't `sample()` check that `frac` is between 0 and 1 somewhere?

Doc improvement suggestion:

Could anyone confirm that `replace=True|False` means allowing|disallowing sampling the same row more than once?

Methinks the docs could use an update to make what `replace` does clearer for newcomers - or at least for those who aren't familiar with `numpy`.