A service that acts as a chain-of-command over a number of {@link org.apache.tapestry5.ioc.ObjectProvider}, but allows for the case where no object may be provided.
This service is itself a key part of Tapestry's general injection mechanism; it is used when instantiating a service implementation instance, invoking module methods (service builder, decorator, or contribution methods), when {@linkplain ObjectLocator#autobuild(Class) autobuilding} objects of any type.
As of Tapestry 5.3, the MasterObjectProvider allows injection of {@link org.apache.tapestry5.ioc.OperationTracker} as aspecial case (not based on a contributed ObjectProvider).