struct to model markdown fields

namespace Root.Core.Models.Fields
{
    using System;

    using Microsoft.AspNetCore.Html;

    using Markdig;
    public readonly struct MarkdownField
    {
        private readonly string _markup;

        public MarkdownField(string markdown)
        {
            RawMarkdown = markdown;

            if (String.IsNullOrEmpty(RawMarkdown))
            {
                _markup = String.Empty;
            }
            else
            {
                _markup = Markdown.ToHtml(
                    RawMarkdown,
                    new MarkdownPipelineBuilder().UseAdvancedExtensions().Build());
            }
        }

        public static implicit operator MarkdownField(string input)
        {
            return new MarkdownField(input);
        }

        public static implicit operator string(MarkdownField input)
        {
            return input.ToString();
        }

        public static implicit operator HtmlString(MarkdownField input)
        {
            return new HtmlString(input.ToString());
        }

        public string RawMarkdown { get; }

        public HtmlString Markup
        {
            get
            {
                return new HtmlString(_markup);
            }
        }

        public override string ToString()
        {
            //TODO: WebUtility.HtmlEncode?
            return Markup.ToString();
        }
    }
}