/// <summary>
/// Returns a regex for the specified format expression.
/// </summary>
/// <param name="format">
/// The format expression.
/// Format expression syntax:
///     * = Any number of chars (.*?)
///     ? = Any single character (.)
///     # = A single digit (\d)
///     % = A single character (\w)
///     Other input characters will be escaped using Regex.Escape(...).
/// </param>
/// <param name="formatDescriptor">The format descriptor for the format expression (e.g. "dd-mm-YYYY").</param>
/// <returns></returns>
public static Regex ToRegex(string format) {
    format = format.Replace("%", "%CHARACTER%").Replace("*", "%STAR%")
        .Replace("#", "%DIGIT%").Replace("?", "%QUESTIONMARK%");
    
    format = Regex.Escape(format);
    
    format = format.Replace("%STAR%", @".*?").Replace("%DIGIT%", @"\d")
        .Replace("%CHARACTER%", @"\w").Replace("%QUESTIONMARK%", @".");
    
    return new Regex(String.Format("^{0}$", format), RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.Singleline);
}