public static void RegisterHtmlToFlowTagConverter(string htmlTag, TagConverter converter)
 {
     _htmlTagConverterInstances.Add(htmlTag, converter);
 }
        /// <summary>
        /// Register a TagConverter to support related tag
        /// </summary>
        /// <param name="converter"></param>
        public static void RegisterFlowToHtmlTagConverter(string flowTag, TagConverter converter)
        {
            Type type = converter.GetType().BaseType;

            Dictionary<string, TagConverter> mapping;

            if (_flowTagConverterInstances.TryGetValue(type, out mapping))
                mapping.Add(flowTag, converter);

            else
                _flowTagConverterInstances.Add(type, new Dictionary<string, TagConverter>() { { flowTag, converter } });
        }