https://logback.qos.ch/manual/ does not state what version of Logback it refers to.
There is no link to older versions of Logback.

My personal use case:
The documentation told me that <configuration scanPeriod=...> is optional, but this is a new feature in 1.3.0-alpha, and not present in 1.2.3 which we're using because, well, alpha.
Effect was that scan="true" would not have any effect because that's the way how 1.2.3 works (unfortunately without an error message so I had to validate that behaviour with a debugger).

Other people will likely be hit by other differences between 1.2.3 and 1.3.0.

I made this "Blocker" because the unavailability of version-aligned documentation for anybody who doesn't use 1.3.0-alpha is potentially blocking their development work.
Feel free to adjust priority if this is inappropriate.