Under https://readthedocs.org/projects/pillow/versions/ I only see latest and stable. Perhaps this should contain a list of all versions?

Trying various urls randomly, I can also see 3.0.x docs with a green version number in the bottom left (same as 3.1.x). If I try 4.0.x, 4.1.x, 4.2.x, 5.1.x it also shows docs for that version, but with a red banner in the bottom left. 7.0.x and 7.1.x don't work at all (404 error).

As a maintainer I see a list of the other versions:

No obvious difference there between 3.0.x, 4.0.x or 7.0.x., etc.

In the middle of https://assets.readthedocs.org/static/javascript/readthedocs-doc-embed.js, there is

t.is_sphinx_builder()&&t.is_rtd_like_theme()?$("div.rst-other-versions").html(e.html):$("body").append(e.html)

This makes me think that for our theme, the lower left red banner is the 'banner that appears on the top of every page'.

Note that we are already injecting content into the theme, so if we wanted, we could customise it further.

For 3.0.x and 3.1.x, where we don't have the red in the lower left, there is a console error, 'Error loading Read the Docs footer'. This is presumably caused by a 404 from an API GET request, which in turn is caused by a double slash in the API URL. However, 3.2.x does have the red in the lower left.