ports/pkg incompatibility, os/libc api changes

[M. MacDonald]

On Fri, 6 Nov 2015 17:32:02 +0200, Konstantin Belousov
<kostikbel at gmail.com> wrote:

>There is no formal statement about the guarantees the project provides,
>but the essence is that the compatibility is backward (and not forward,
>as you found).  In other words, we guarantee that a binary compiled and
>worked on the previous version of the system, works on the newer version,
>but not in reverse. 

"Backwardly compatible" generally means that, although designed
and built for the new one, it will still run on the old one
(i.e., it's compatible in a backward direction).   Something
built on and for the old one that still runs on the new one is
often called "investment-preserving".