Berkeley DB file compatibility between versions ?

[Skybuck]

How compatibile are Berkley DB files with different versions of itself ?

For example:

Are all Berkeley DB 4.x file versions compatible with each other ?

Or is for example Berkeley DB 4.8.30 only compatible with it's own version 4.80.30 ?

So for example could Berkeley DB 4.05.20 access 4.80.30 files ??