public static function extension($file, $separator = self::SEPARATOR_BOTH){
        return self::validate($file, $separator) ? substr($file, strrpos($file, '.') + 1) : false;
    }
public static function extension($file, $separator = self::SEPARATOR_BOTH){
        return self::validate($file, $separator) ? substr($file, strrpos($file, '.') + 1) : false;
    }
public static function extension ( $ file , $ separator = self :: SEPARATOR_BOTH ) { return self :: validate ( $ file , $ separator ) ? substr ( $ file , strrpos ( $ file , '.' ) + 1 ) : false ; }
Return the extension of a file or false on invalid filenames
@static
@param string $file
@param string $separator
@return bool|string
Return the extension of a file or false on invalid filenames