question regarding policy for patches to out-of-support branches

I was having a discussion regarding out-of-support branches and effort
to keep them building, but could not for the life of me find any actual
documented policy (although I distinctly remember that we do something...).

I did find fleeting references, for example:

8<-----------------------
commit c705646b751e08d584f6eeb098f1ed002aa7b11c
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Date: 2022-09-21 13:52:38 -0400

<snip>

Per project policy, this is a candidate for back-patching into
out-of-support branches: it suppresses annoying compiler warnings
but changes no behavior. Hence, back-patch all the way to 9.2.
8<-----------------------

and on its related thread:

8<-----------------------
However, I think that that would *not* be fit material for
back-patching into out-of-support branches, since our policy
for them is "no behavioral changes".
8<-----------------------

Is the policy written down somewhere, or is it only project lore? In
either case, what is the actual policy?

Thanks,

--
Joe Conway
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com