navigatorObservers property
A builder function that returns a list of observes
Why isn't this a list of navigatorObservers? The reason for that is a NavigatorObserver instance can only be used by a single Navigator, so unless you're using a one single router or you don't want your nested routers to inherit observers make sure navigatorObservers builder always returns fresh observer instances.
Implementation
final NavigatorObserversBuilder navigatorObservers;