#include <DataFormats/Common/interface/RefToBase.h>
Description: Interface to a reference to an item based on the base class of the item
Usage: Using an edm:RefToBase<T> allows one to hold references to items in different containers within the edm::Event where those objects are only related by a base class, T.
Cast to concrete type can be done via the castTo<REF> function template. This function throws an exception if the type passed as REF does not match the concrete reference type.