ASP.NET MVC: SELECT with OPTGROUP from dictionary of select list items

gistfile1.cs

	public static class HtmlExtensions
	{
		public static IHtmlString DropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, Dictionary<string, IEnumerable<SelectListItem>> selectList)
		{
			/*
			 * <select name="tmodel">
			 *   <optgroup title="Items">
			 *   <option value="item">Item</option>
			 * </select>
			 */

			var select = new TagBuilder("select");
			select.Attributes.Add("name", ExpressionHelper.GetExpressionText(expression));

			var optgroups = new StringBuilder();

			foreach (var kvp in selectList)
			{
				var optgroup = new TagBuilder("optgroup");
				optgroup.Attributes.Add("label", kvp.Key);

				var options = new StringBuilder();

				foreach (var item in kvp.Value)
				{
					var option = new TagBuilder("option");

					option.Attributes.Add("value", item.Value);
					option.SetInnerText(item.Text);

					if (item.Selected)
					{
						option.Attributes.Add("selected", "selected");
					}

					options.Append(option.ToString(TagRenderMode.Normal));
				}

				optgroup.InnerHtml = options.ToString();

				optgroups.Append(optgroup.ToString(TagRenderMode.Normal));
			}

			select.InnerHtml = optgroups.ToString();

			return MvcHtmlString.Create(select.ToString(TagRenderMode.Normal));
		}
	}

Oh. There's some opportunity for HTML injection here. Should probably escape some strings.