Remove unwanted HTML tags from string

gistfile1.cs

/// <summary>
/// Reference: http://stackoverflow.com/questions/307013/how-do-i-filter-all-html-tags-except-a-certain-whitelist
/// </summary>
/// <param name="source"></param>
/// <returns></returns>
public string RemoveUnwantedTags(string source)
{
    const string acceptable = "b|i|p";
    const string stringPattern = @"</?(?(?=" + acceptable + @")notag|[a-zA-Z0-9]+)(?:\s[a-zA-Z0-9\-]+=?(?:(["",']?).*?\1?)?)*\s*/?>";
    return Regex.Replace(source, stringPattern, "");
}