Can I create a package with friendly modules

[forkit]

Is it possible to create a package.d, consisting of (for 
example), two modules, where each module can access private 
declarations within each other.

In essence, declaring 'a module level friendship', or a kind of 
'extended module' if you want.

I might still want to add another module to the package, that is 
NOT part of that friendship between those other two modules, but 
is otherwise related to the solution.