Documentation Link

https://matplotlib.org/devdocs/api/_as_gen/matplotlib.axes.Axes.contourf.html
https://matplotlib.org/devdocs/api/_as_gen/matplotlib.axes.Axes.tricontourf.html

Problem

This applies to tricontour/f and contour/f.

The documentation of the contour functions' levels parameter states:

            If an int *n*, use `~matplotlib.ticker.MaxNLocator`, which tries
            to automatically choose no more than *n+1* "nice" contour levels
            between *vmin* and *vmax*.

This is not true, the levels are always chosen betwen Z.min() and Z.max(). There is no way for the user to influence this when using the integer parameter variant. See implementation in contour.py: ContourSet._autolev().
Especially deceptive because the text as written is very much what one would expect, but that functionality does not exist (and never has).

Suggested improvement

Change "between vmin and vmax" to something like "in the data range" or more explicit "between minimum and maximum values of Z"