[2435] Add documentation for RRsetCollectionPtr

src/lib/dns/rrset_collection_base.h

@@ -171,6 +171,10 @@ public:
     }
 };
 
+/// \brief A pointer-like type pointing to an \c RRsetCollection object.
+///
+/// This type is used to handle RRsetCollections in a polymorphic manner
+/// in the BIND 10 codebase.
 typedef boost::shared_ptr<RRsetCollectionBase> RRsetCollectionPtr;
 
 } // end of namespace dns