Is the FreeBSD ABI compatibility policy documented anywhere

[Stef Walter]

It seems that FreeBSD has an ABI compatibility policy where major
versions remain ABI and API compatible throughout minor point versions.
That is to say that the kernel interfaces and libraries for (eg)
7-STABLE, 7.1-RELEASE, 7.2-RELEASE are not supposed to change.

Is this a policy of the project? If so, is it documented anywhere? Or is
it just a convention?

Cheers,

Stef