Where can I find documentation for matplotlib()?

edit

I was trying to implement the code in the answer post by ADuC812 in combine sage plot with matplotlib. The poster used called matplotlib(), however, I could not find this method anywhere.

Essentially,

g=plot(sin(x))
from matplotlib.figure import Figure
figure = Figure()
main_plot = figure.add_axes((0.2,0.2,0.7,0.7))
g.matplotlib('a.svg', figure=figure, sub=main_plot)

Is matplotlib() supposed to be part of sagemath or matplotlib? Would you provide a link to the documentation for it? Thanks in advance!

Edit: Found this: Get list of coordinates from plot object

And trying:

var('x,y')
p = implicit_plot(x^2+y^2-1,(x,-2,2),(y,-2,2),plot_points=4)
P = p.matplotlib()
type(P)

I get

<class 'matplotlib.figure.Figure'>