namespace ZKEACMS.Message.TagHelps
{
 [HtmlTargetElement("markdown", TagStructure = TagStructure.NormalOrSelfClosing)]
 [HtmlTargetElement(Attributes = "markdown")]
 public class MarkdownTagHelper : TagHelper
 {
 public ModelExpression Content { get; set; }
 public async override Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
 {
 if (output.TagName == "markdown")
 {
 output.TagName = null;
 }
 output.Attributes.RemoveAll("markdown");
 var content = await GetContent(output);
 var markdown = WebUtility.HtmlEncode(WebUtility.HtmlDecode(content));
 var html = CommonMarkConverter.Convert(markdown);
 output.Content.SetHtmlContent(html ?? "");
 }
 private async Task GetContent(TagHelperOutput output)
 {
 if (Content == null)
 return (await output.GetChildContentAsync()).GetContent();
 return Content.Model?.ToString();
 }
 }
}

@addTagHelper *, ZKEACMS.Message

<markdown>@item.CommentContent</markdown>