asp.net mvc boolean html attribute helper

public static class HtmlExtension
    {
        private static string[] htmlBooleanAttributes = (new[] { "selected", "checked", "disabled", "readonly", "multiple" }).SelectMany(x => new[] {  x + "=\"\"",  x + "=\"false\"" }).ToArray();
        public static IHtmlString HackIt(this IHtmlString htmlString)
        {
            if (htmlString != null)
            {
                string str = htmlString.ToString();
                foreach (var attribute in htmlBooleanAttributes)
                {
                    int index = -1;
                    do
                    {
                        var searchIndex = index == -1 ? 0 : index;
                        index = str.IndexOf(attribute, searchIndex, StringComparison.OrdinalIgnoreCase);
                        if (index > -1)
                            str = str.Remove(index, attribute.Length);
                    } while (index > -1);
                }
                return new HtmlString(str);
            }
            return htmlString;
        }
    }