Actually, the docstrings for axes, etc don't need updated. They already accepted the alpha kwarg. I should update the default matplotlibrc file, though.

$ find . -iname '*rc'
./doc/matplotlibrc
./doc/pyplots/matplotlibrc
./lib/matplotlib/mpl-data/matplotlibrc
./lib/matplotlib/tests/test_rcparams.rc

Which one of these do I need to update?

Without any authority on the matter, I would say:

matplotlibrc.template
./lib/matplotlib/mpl-data/matplotlibrc
./doc/pyplots/matplotlibrc

While digging, I found lib/matplotlib/mpl-data/matplotlib.conf, can anyone tell me if this is still used?

Clearly this is highlighting an issue.

I've made an issue for discussion on the various rc files and the conf file to keep the conversations separate from this PR.

That's a great idea. Thanks.

I also found lib/matplotlib/mpl-data/matplotlib.conf.template too.

Wait a sec, I found this in the .gitignore file:

# Things specific to this project #
###################################
lib/matplotlib/mpl-data/matplotlib.conf
lib/matplotlib/mpl-data/matplotlibrc

matplotlibrc.template is the one to update.

Right, I will remove the update to the one under the docs directory. Thank you.

Looks fine to me. +1