public function addCover($input, $options = array(), $type = null)
    {
        $options['input'] = ($this->version9 ? '--' : '') . 'cover';
        $options['inputArg'] = $this->ensureUrlOrFile($input, $type);
        $this->_objects[] = $this->ensureUrlOrFileOptions($options);
        return $this;
    }