The HtmlTextWriter.WriteUrlEncodedString(string, bool) method encodes characters that could be considered URL delimiters (dependent on the setting of argument) into strings of the form %xx, if the ASCII code is less than 128; otherwise, %uxxxx, where x is a hexadecimal digit.
The HtmlTextWriter.WriteEncodedUrl(string) and HtmlTextWriter.WriteEncodedUrlParameter(string) methods use the HtmlTextWriter.WriteUrlEncodedString(string, bool) method as a utility method.