Compatibility Between Releases Policy

[Jason C. Wells]

Where is the policy regarding compatibility between releases documented?

I recall reading once upon a time that FreeBSD won't break compatibility 
for the duration of a major point release.  If a third party wrote 
software for 6.0 it would be perfectly compatible with 6.1, 6.2 and on.

The reason I ask is that I am considering the wisdom of running 
portupgraed with each minor point release.

Thanks,
Jason C. Wells