[ros-users] stack manifest.xml dependencies

Is declaring stack dependencies in the stack manifest.xml optional?
What is the best practice--should a stack ideally declare dependencies
on all stacks that contain a package that is depended upon in one of
its own packages' manifests (wow, that was a convoluted sentence)?

If so can I easily test whether all the right dependencies have been
declared? Will 'rosstack depends mystack' do that? How about any
extraneous dependencies, is there a way to find those?

Thanks,
Pat