/// <summary>
        /// 将文档中所有的uri属性转换为绝对的uri。
        /// </summary>
        /// <param name="document">要执行转换的文档</param>
        /// <param name="resolveInternalReference">是否转换页内 uri</param>
        public static void ResolveUriToAbsoluate(this IHtmlDocument document, bool resolveInternalReference)
        {
            if (document == null)
            {
                throw new ArgumentNullException("document");
            }


            var baseUri = document.DocumentUri;

            if (baseUri == null)
            {
                throw new InvalidOperationException();
            }

            foreach (var attribute in document.AllElements().SelectMany(e => e.Attributes()).Where(a => document.HtmlSpecification.IsUriValue(a)).ToArray())
            {
                var value = attribute.Value();
                if (string.IsNullOrEmpty(value))
                {
                    continue;
                }

                Uri uri;

                if (!Uri.TryCreate(baseUri, value, out uri))
                {
                    continue;
                }

                if (uri.Equals(baseUri) && !resolveInternalReference)
                {
                    continue;
                }


                attribute.Element.SetAttribute(attribute.Name, uri.AbsoluteUri);
            }
        }