public function register($class, $transforms)
    {
        if (!is_array($transforms)) {
            $transforms = array($transforms);
        }
        foreach ($transforms as $t) {
            if (!($t instanceof TransformationInterface)) {
                throw new \InvalidArgumentException("Only instances of TransformationInterface can be registered");
            }
        }

        if (!isset($this->transforms[$class])) {
            $this->classes[] = $class;
            $this->transforms[$class] = array();
        }

        foreach ($transforms as $t) {
            $this->transforms[$class][] = $t;
        }
    }