> $source Source array for possible extensions * * @return string * * @since 1.0.0 */ public static function generateExtension(array $source = null) : string { if ($source === null) { $source = self::$extensions; } $key = \mt_rand(0, \count($source) - 1); return $source[$key][\mt_rand(0, \count($source[$key]) - 1)]; } }