public function append($selector, $value)
    {
        $oldValue = $this->get($selector);
        if ($oldValue) {
            if (!is_array($oldValue)) {
                $oldValue = (array) $oldValue;
            }
            $oldValue[] = $value;
            $value = $oldValue;
        }

        $this->set($selector, $value);
        return $this;
    }