The Dart pubspec.yaml file allows you to add a dependency_overrides section to during development.
The dependency_overrides section allows you to specify an alternate location for any package dependency.
This often useful during development if you have an associated package that you are also developing.
The dependency_override allows your package to use the associated packages code from your local disk rather than from pub.dev.
In the above example the pub_release project is dependant on dcli.
As I'm also the developer of dcli I often make changes to dcli to support pub_release features.
I find it easier to make dcli changes and test them in pub_release before I publish dcli to pub.dev.
The dependency_override allows me to work on both code bases simultaneous.
When it comes time to publish my package I need to remove the dependency_overrides as pub.dev only allows you to have dependencies on other published packages.
pub_release supports dependency_overrides by automatically removing them during the release process.
Once the package has been published it restores the original overrides.
The support of dependency_overrides is particularly important when doing multi-package releases as it is normally to have overrides for each of the related packages.