/// <summary>
        /// Asynchronously reads XML data into the current <see cref="AtomEntry"/>.
        /// </summary>
        /// <exception cref="InvalidDataException">
        /// Thrown when an Invalid Data error condition occurs.
        /// </exception>
        /// <param name="reader">
        /// The reader from which to read.
        /// </param>
        /// <returns>
        /// A <see cref="Task"/> representing the operation.
        /// </returns>
        public async Task ReadXmlAsync(XmlReader reader)
        {
            Contract.Requires<ArgumentNullException>(reader != null, "reader");

            this.Author = null;
            this.Content = null;
            this.Id = null;
            this.Links = null;
            this.Published = DateTime.MinValue;
            this.Title = null;
            this.Updated = DateTime.MinValue;

            reader.Requires(await reader.MoveToDocumentElementAsync("entry"));

            Dictionary<string, Uri> links = null;
            await reader.ReadAsync();

            while (reader.NodeType == XmlNodeType.Element)
            {
                string name = reader.Name;

                switch (name)
                {
                    case "title":

                        this.Title = await reader.ReadElementContentAsync(StringConverter.Instance);
                        break;

                    case "id":

                        this.Id = await reader.ReadElementContentAsync(UriConverter.Instance);
                        break;

                    case "author":
                        
                        await reader.ReadAsync();
                        reader.EnsureMarkup(XmlNodeType.Element, "name");
                        this.Author = await reader.ReadElementContentAsync(StringConverter.Instance);
                        reader.EnsureMarkup(XmlNodeType.EndElement, "author");
                        await reader.ReadAsync();
                        break;

                    case "published":

                        this.Published = await reader.ReadElementContentAsync(DateTimeConverter.Instance);
                        break;

                    case "updated":

                        this.Updated = await reader.ReadElementContentAsync(DateTimeConverter.Instance);
                        break;

                    case "link":

                        if (links == null)
                        {
                            links = new Dictionary<string, Uri>();
                        }

                        var href = reader.GetRequiredAttribute("href");
                        var rel = reader.GetRequiredAttribute("rel");
                        links[rel] = UriConverter.Instance.Convert(href);
                        await reader.ReadAsync();
                        break;

                    case "content":

                        this.Content = await ParsePropertyValueAsync(reader, 0);
                        break;

                    default: throw new InvalidDataException(); // TODO: Diagnostics : unexpected start tag
                }
            }

            reader.EnsureMarkup(XmlNodeType.EndElement, "entry");
            await reader.ReadAsync();

            if (links != null)
            {
                this.Links = new ReadOnlyDictionary<string, Uri>(links);
            }
        }
        /// <summary>
        /// Asynchronously reads XML data into the current <see cref="AtomFeed"/>.
        /// </summary>
        /// <exception cref="InvalidDataException">
        /// Thrown when an Invalid Data error condition occurs.
        /// </exception>
        /// <param name="reader">
        /// The reader from which to read.
        /// </param>
        /// <returns>
        /// A <see cref="Task"/> representing the operation.
        /// </returns>
        public async Task ReadXmlAsync(XmlReader reader)
        {
            Contract.Requires<ArgumentNullException>(reader != null, "reader");

            this.Author = null;
            this.Entries = null;
            this.GeneratorVersion = null;
            this.Id = null;
            this.Links = null;
            this.Messages = null;
            this.Pagination = Pagination.None;
            this.Title = null;
            this.Updated = DateTime.MinValue;

            reader.Requires(await reader.MoveToDocumentElementAsync("feed"));
            var documentElementName = reader.Name;

            List<AtomEntry> entries = null;
            Dictionary<string, Uri> links = null;
            List<Message> messages = null;

            await reader.ReadAsync();

            while (reader.NodeType == XmlNodeType.Element)
            {
                string name = reader.Name;

                switch (name)
                {
                    case "title":

                        this.Title = await reader.ReadElementContentAsync(StringConverter.Instance);
                        break;

                    case "id":

                        this.Id = await reader.ReadElementContentAsync(UriConverter.Instance);
                        break;

                    case "author":

                        await reader.ReadAsync();
                        reader.EnsureMarkup(XmlNodeType.Element, "name");
                        this.Author = await reader.ReadElementContentAsync(StringConverter.Instance);
                        reader.EnsureMarkup(XmlNodeType.EndElement, "author");
                        await reader.ReadAsync();
                        break;

                    case "generator":

                        // string build = reader.GetRequiredAttribute("build"); // TODO: Incorporate build number? Build number sometimes adds a fifth digit.
                        string version = reader.GetRequiredAttribute("version");
                        this.GeneratorVersion = VersionConverter.Instance.Convert(string.Join(".", version));
                        await reader.ReadAsync();
                        break;

                    case "updated":

                        this.Updated = await reader.ReadElementContentAsync(DateTimeConverter.Instance);
                        break;

                    case "entry":

                        var entry = new AtomEntry();

                        if (entries == null)
                        {
                            entries = new List<AtomEntry>();
                        }

                        entries.Add(entry);

                        await entry.ReadXmlAsync(reader);
                        break;

                    case "link":

                        var href = reader.GetRequiredAttribute("href");
                        var rel = reader.GetRequiredAttribute("rel");

                        if (links == null)
                        {
                            links = new Dictionary<string, Uri>();
                        }

                        links[rel] = UriConverter.Instance.Convert(href);
                        await reader.ReadAsync();
                        break;

                    case "s:messages":

                        bool isEmptyElement = reader.IsEmptyElement;
                        await reader.ReadAsync();

                        if (messages == null)
                        {
                            messages = new List<Message>();
                        }

                        if (isEmptyElement)
                        {
                            continue;
                        }

                        while (reader.NodeType == XmlNodeType.Element && reader.Name == "s:msg")
                        {
                            var value = reader.GetRequiredAttribute("type");
                            var type = EnumConverter<MessageType>.Instance.Convert(value);
                            var text = await reader.ReadElementContentAsStringAsync();
                            
                            messages.Add(new Message(type, text));
                        }

                        if (reader.NodeType == XmlNodeType.EndElement)
                        {
                            reader.EnsureMarkup(XmlNodeType.EndElement, "s:messages");
                            await reader.ReadAsync();
                        }

                        break;

                    case "opensearch:itemsPerPage":

                        int itemsPerPage = await reader.ReadElementContentAsync(Int32Converter.Instance);
                        this.Pagination = new Pagination(itemsPerPage, this.Pagination.StartIndex, this.Pagination.TotalResults);
                        break;

                    case "opensearch:startIndex":

                        int startIndex = await reader.ReadElementContentAsync(Int32Converter.Instance);
                        this.Pagination = new Pagination(this.Pagination.ItemsPerPage, startIndex, this.Pagination.TotalResults);
                        break;

                    case "opensearch:totalResults":

                        int totalResults = await reader.ReadElementContentAsync(Int32Converter.Instance);
                        this.Pagination = new Pagination(this.Pagination.ItemsPerPage, this.Pagination.StartIndex, totalResults);
                        break;

                    default: throw new InvalidDataException(string.Format("Unexpected start tag: {0}", reader.Name)); // TODO: Improved diagnostics
                }
            }

            reader.EnsureMarkup(XmlNodeType.EndElement, documentElementName);
            await reader.ReadAsync();

            if (entries != null)
            {
                this.Entries = new ReadOnlyCollection<AtomEntry>(entries);
            }

            if (links != null)
            {
                this.Links = new ReadOnlyDictionary<string, Uri>(links);
            }

            if (messages != null)
            {
                this.Messages = new ReadOnlyCollection<Message>(messages);
            }
        }