You are reading an old version of the documentation (v3.1.3). For the latest version see https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.set_xmargin.html
Version 3.1.3
matplotlib
Fork me on GitHub

matplotlib.axes.Axes.set_xmargin

Axes.set_xmargin(self, m)

Set padding of X data limits prior to autoscaling.

m times the data interval will be added to each end of that interval before it is used in autoscaling. For example, if your data is in the range [0, 2], a factor of m = 0.1 will result in a range [-0.2, 2.2].

Negative values -0.5 < m < 0 will result in clipping of the data range. I.e. for a data range [0, 2], a factor of m = -0.1 will result in a range [0.2, 1.8].

Parameters:
m : float greater than -0.5