How is the drop-down menu created after the CMake Docs is built from the Help directory?

[hwhsu1231 (Haowei Hsu)]

I thinks this topic is related to this comment by @brad.king:

Doc versioning mechanism

We configure sphinx with a custom template directory here. That directory contains a custom layout template, which has special version switch code activated by passing -A versionswitch=1 when running sphinx. The version switch code loads version_switch.js, which we publish on the web host here. The addition of the “This documents an old version of” and “Click here to see the latest release” is done by internal infrastructure we use to prepare the documentation for publication on cmake.org. B…