/// <summary>
		/// Fetches the message summaries for the messages between the two indexes (inclusive)
		/// that have a higher mod-sequence value than the one specified.
		/// </summary>
		/// <remarks>
		/// <para>Fetches the message summaries for the messages between the two
		/// indexes (inclusive) that have a higher mod-sequence value than the one
		/// specified.</para>
		/// <para>It should be noted that if another client has modified any message
		/// in the folder, the IMAP server may choose to return information that was
		/// not explicitly requested. It is therefore important to be prepared to
		/// handle both additional fields on a <see cref="IMessageSummary"/> for
		/// messages that were requested as well as summaries for messages that were
		/// not requested at all.</para>
		/// </remarks>
		/// <returns>An enumeration of summaries for the requested messages.</returns>
		/// <param name="min">The minimum index.</param>
		/// <param name="max">The maximum index, or <c>-1</c> to specify no upper bound.</param>
		/// <param name="modseq">The mod-sequence value.</param>
		/// <param name="items">The message summary items to fetch.</param>
		/// <param name="fields">The desired header fields.</param>
		/// <param name="cancellationToken">The cancellation token.</param>
		/// <exception cref="System.ArgumentOutOfRangeException">
		/// <para><paramref name="min"/> is out of range.</para>
		/// <para>-or-</para>
		/// <para><paramref name="max"/> is out of range.</para>
		/// </exception>
		/// <exception cref="System.ArgumentNullException">
		/// <paramref name="fields"/> is <c>null</c>.
		/// </exception>
		/// <exception cref="System.ArgumentException">
		/// <paramref name="fields"/> is empty.
		/// </exception>
		/// <exception cref="System.ObjectDisposedException">
		/// The <see cref="ImapClient"/> has been disposed.
		/// </exception>
		/// <exception cref="ServiceNotConnectedException">
		/// The <see cref="ImapClient"/> is not connected.
		/// </exception>
		/// <exception cref="ServiceNotAuthenticatedException">
		/// The <see cref="ImapClient"/> is not authenticated.
		/// </exception>
		/// <exception cref="FolderNotOpenException">
		/// The <see cref="ImapFolder"/> is not currently open.
		/// </exception>
		/// <exception cref="System.NotSupportedException">
		/// The <see cref="ImapFolder"/> does not support mod-sequences.
		/// </exception>
		/// <exception cref="System.OperationCanceledException">
		/// The operation was canceled via the cancellation token.
		/// </exception>
		/// <exception cref="System.IO.IOException">
		/// An I/O error occurred.
		/// </exception>
		/// <exception cref="ImapProtocolException">
		/// The server's response contained unexpected tokens.
		/// </exception>
		/// <exception cref="ImapCommandException">
		/// The server replied with a NO or BAD response.
		/// </exception>
		public override IList<IMessageSummary> Fetch (int min, int max, ulong modseq, MessageSummaryItems items, HashSet<string> fields, CancellationToken cancellationToken = default (CancellationToken))
		{
			if (min < 0 || min >= Count)
				throw new ArgumentOutOfRangeException ("min");

			if (max != -1 && max < min)
				throw new ArgumentOutOfRangeException ("max");

			if (fields == null)
				throw new ArgumentNullException ("fields");

			if (fields.Count == 0)
				throw new ArgumentException ("The set of header fields cannot be empty.", "fields");

			if (!SupportsModSeq)
				throw new NotSupportedException ("The ImapFolder does not support mod-sequences.");

			CheckState (true, false);

			var query = FormatSummaryItems (ref items, fields);
			var command = string.Format ("FETCH {0} {1} (CHANGEDSINCE {2})\r\n", GetFetchRange (min, max), query, modseq);
			var ic = new ImapCommand (Engine, cancellationToken, this, command);
			var ctx = new FetchSummaryContext (items);

			ic.RegisterUntaggedHandler ("FETCH", FetchSummaryItems);
			ic.UserData = ctx;

			Engine.QueueCommand (ic);
			Engine.Wait (ic);

			ProcessResponseCodes (ic, null);

			if (ic.Response != ImapCommandResponse.Ok)
				throw ImapCommandException.Create ("FETCH", ic);

			return AsReadOnly (ctx.Results.Values);
		}