private static function _extractBytes($byteString, $start, $length) {
        if (function_exists('mb_substr')) {
            return mb_substr($byteString, $start, $length, '8bit');
        }
        return substr($byteString, $start, $length);
    }
private static function _extractBytes($byteString, $start, $length) {
        if (function_exists('mb_substr')) {
            return mb_substr($byteString, $start, $length, '8bit');
        }
        return substr($byteString, $start, $length);
    }
private static function _extractBytes ( $ byteString , $ start , $ length ) { if ( function_exists ( 'mb_substr' ) ) { return mb_substr ( $ byteString , $ start , $ length , '8bit' ) ; } return substr ( $ byteString , $ start , $ length ) ; }
Returns the bytes of the given string specified by the start and length
parameters.

@param string $byteString The string from which to extract the bytes.
@param int $start Start position.
@param int $length Number of bytes to extract.
@return string Subset of bytes from given string.
Returns the bytes of the given string specified by the start and length parameters .