pkgng multi-repository support description

[Andriy Gapon]

Is there a document that describes how pkgng multi-repository support works?
I am trying to understand what pkgng does when different versions of the same
package are present in different repositories.

Practically, I want to achieve the following.
One repository is designated as primary.  If a package is present in the primary
repository, then its presence in other repositories is completely ignored.

Alternatively, the following could also work for me.
A package remembers from what repository it was originally installed and all
future upgrades are taken from the same repository.

What I want to avoid is a package flip-flopping between being installed from
different repositories depending on their update pace.  This is useful e.g. when
I have my local repository for some packages that I want to build with special
options but I also want to install all other packages from some other repository
which is not under my control.  So I fear that the other repository gets a newer
version of a package than what my repository has, then pkg upgrade would upgrade
the package and thus it won't have any customizations until my repository
catches up.

Thank you very much.

P.S. https://github.com/freebsd/pkg#multirepos seems to be outdated?
-- 
Andriy Gapon