private void registerLegacyV6Factories() {
        // Prepare version specifications to use when adding routable factories.
        VersionSpecification version6 = new VersionSpecification(6, 221);

        List<VersionSpecification> from6 = List.of(version6);

        // 6.x serialization (keep alphabetized please)
        putRoutableFactory(MESSAGE_CREATEVISITOR, new RoutableFactories60.CreateVisitorMessageFactory(), from6);
        putRoutableFactory(MESSAGE_DESTROYVISITOR, new RoutableFactories60.DestroyVisitorMessageFactory(), from6);
        putRoutableFactory(MESSAGE_DOCUMENTLIST, new RoutableFactories60.DocumentListMessageFactory(), from6);
        putRoutableFactory(MESSAGE_EMPTYBUCKETS, new RoutableFactories60.EmptyBucketsMessageFactory(), from6);
        putRoutableFactory(MESSAGE_GETBUCKETLIST, new RoutableFactories60.GetBucketListMessageFactory(), from6);
        putRoutableFactory(MESSAGE_GETBUCKETSTATE, new RoutableFactories60.GetBucketStateMessageFactory(), from6);
        putRoutableFactory(MESSAGE_GETDOCUMENT, new RoutableFactories60.GetDocumentMessageFactory(), from6);
        putRoutableFactory(MESSAGE_MAPVISITOR, new RoutableFactories60.MapVisitorMessageFactory(), from6);
        putRoutableFactory(MESSAGE_PUTDOCUMENT, new RoutableFactories60.PutDocumentMessageFactory(), from6);
        putRoutableFactory(MESSAGE_QUERYRESULT, new RoutableFactories60.QueryResultMessageFactory(), from6);
        putRoutableFactory(MESSAGE_REMOVEDOCUMENT, new RoutableFactories60.RemoveDocumentMessageFactory(), from6);
        putRoutableFactory(MESSAGE_REMOVELOCATION, new RoutableFactories60.RemoveLocationMessageFactory(), from6);
        putRoutableFactory(MESSAGE_STATBUCKET, new RoutableFactories60.StatBucketMessageFactory(), from6);
        putRoutableFactory(MESSAGE_UPDATEDOCUMENT, new RoutableFactories60.UpdateDocumentMessageFactory(), from6);
        putRoutableFactory(MESSAGE_VISITORINFO, new RoutableFactories60.VisitorInfoMessageFactory(), from6);
        putRoutableFactory(REPLY_CREATEVISITOR, new RoutableFactories60.CreateVisitorReplyFactory(), from6);
        putRoutableFactory(REPLY_DESTROYVISITOR, new RoutableFactories60.DestroyVisitorReplyFactory(), from6);
        putRoutableFactory(REPLY_DOCUMENTIGNORED, new RoutableFactories60.DocumentIgnoredReplyFactory(), from6);
        putRoutableFactory(REPLY_DOCUMENTLIST, new RoutableFactories60.DocumentListReplyFactory(), from6);
        putRoutableFactory(REPLY_EMPTYBUCKETS, new RoutableFactories60.EmptyBucketsReplyFactory(), from6);
        putRoutableFactory(REPLY_GETBUCKETLIST, new RoutableFactories60.GetBucketListReplyFactory(), from6);
        putRoutableFactory(REPLY_GETBUCKETSTATE, new RoutableFactories60.GetBucketStateReplyFactory(), from6);
        putRoutableFactory(REPLY_GETDOCUMENT, new RoutableFactories60.GetDocumentReplyFactory(), from6);
        putRoutableFactory(REPLY_MAPVISITOR, new RoutableFactories60.MapVisitorReplyFactory(), from6);
        putRoutableFactory(REPLY_PUTDOCUMENT, new RoutableFactories60.PutDocumentReplyFactory(), from6);
        putRoutableFactory(REPLY_QUERYRESULT, new RoutableFactories60.QueryResultReplyFactory(), from6);
        putRoutableFactory(REPLY_REMOVEDOCUMENT, new RoutableFactories60.RemoveDocumentReplyFactory(), from6);
        putRoutableFactory(REPLY_REMOVELOCATION, new RoutableFactories60.RemoveLocationReplyFactory(), from6);
        putRoutableFactory(REPLY_STATBUCKET, new RoutableFactories60.StatBucketReplyFactory(), from6);
        putRoutableFactory(REPLY_UPDATEDOCUMENT, new RoutableFactories60.UpdateDocumentReplyFactory(), from6);
        putRoutableFactory(REPLY_VISITORINFO, new RoutableFactories60.VisitorInfoReplyFactory(), from6);
        putRoutableFactory(REPLY_WRONGDISTRIBUTION, new RoutableFactories60.WrongDistributionReplyFactory(), from6);
    }
Get priority enum instance by its name.

@param name name of priority.
@return priority enum instance, given that <code>name</code> is valid
@throws IllegalArgumentException if priority name is unknown
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/DocumentProtocol.java