How RPMs are marked to agree dependencies only from spesific repos?

How RPMs are marked to agree dependencies only from spesific repos like official Fedora repositories?

As with regular dependencies, weak dependencies MUST be satisfiable within the official Fedora repositories.

Source: Weak Dependencies Policy :: Fedora Docs

Any devs know?

The RPMs are not marked withe which repos to get dependencies from.
Its a policy to only build against Fedora RPMs that is enforced by the koji build system only knowing about Fedora built RPMs.