public function addExtension(string $sExtension, array $aMimes): self
    {
        $this->updateMap(static::$aMapExtensionToMimes, $sExtension, $aMimes);
        foreach ($aMimes as $sMime) {
            $this->updateMap(static::$aMapMimeToExtensions, $sMime, [$sExtension]);
        }
        return $this;
    }