FWIW, the float option for axisbelow seems to already have been evaluated in a not too old past here #6287

Actually I decided to not support float values in axisbelow -- just set zorder if that's what you want to do (in fact, one should just set zorder in all cases).

It appears that commenting out the lines

            if not np.isfinite(posx) or not np.isfinite(posy):
                raise ValueError("posx and posy should be finite values")

in text.py makes the currently failing docs example (custom_scale_example) just build fine... strange.

Edit: should be fixed now, was a silly error on my side.

Apart from minor documentation problems, this looks good on the mpl side of things. I'm trying to stay away from the 3d stuff, so I can't comment on that.
Can I push directly to your branch to fix the couple of doc problems?

🍾