PHP: UTF-8 encoding detection

gistfile1.aw

/**
 * Checks, if passed string is utf-8 encoded or not.
 *
 * @param   string  $string     String to check
 * @return  int     Number of found UTF-8 character
 */
function mp_detectUTF8($string)
{
    return preg_match('%(?:
        [\xC2-\xDF][\x80-\xBF]               # non-overlong 2-byte
        |\xE0[\xA0-\xBF][\x80-\xBF]          # excluding overlongs
        |[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}   # straight 3-byte
        |\xED[\x80-\x9F][\x80-\xBF]          # excluding surrogates
        |\xF0[\x90-\xBF][\x80-\xBF]{2}       # planes 1-3
        |[\xF1-\xF3][\x80-\xBF]{3}           # planes 4-15
        |\xF4[\x80-\x8F][\x80-\xBF]{2}       # plane 16
        )+%xs', $string
    );
}