public static function substring($string, $start = 0, $length = null)
    {
        if (!self::isValid($string)) {
            return false;
        }

        return mb_substr($string, $start, $length);
    }
public static function substring($string, $start = 0, $length = null)
    {
        if (!self::isValid($string)) {
            return false;
        }

        return mb_substr($string, $start, $length);
    }
public static function substring ( $ string , $ start = 0 , $ length = null ) { if ( ! self :: isValid ( $ string ) ) { return false ; } return mb_substr ( $ string , $ start , $ length ) ; }
Get a part of a string

@param string $string The string
@param int $start Starting point
@param int $length Length

@return string
Get a part of a string