You are looking at the files used to build OctoPrint's documentation as published on docs.octoprint.org.
It is implemented through the github workflow under .github/workflows/docs.yaml and relies
on a custom sphinx wrapper located in util/versionselector as well as a little helper
located in util/versions_from_matrix.py.
Builds are triggered via a webhook from OctoPrint/OctoPrint
on pushes and new tagged releases, and on push to master on this repository.
Webhook triggers cause only a single doc version to be rebuilt (if any). Pushes however trigger a full rebuild of all registered doc versions.
To register a new version to be built and served, edit the build matrix configured
in .github/workflows/docs.yaml. Do not use anything but include statements for that or
the version extraction during build will no longer work.