Zend framework Zend_Tag_云-设置选项

如何在Zend_Tag_Cloud上设置minFontSize属性？ 目前看起来是这样，但我得到一个错误：

Decorator不是Zend_Tag_Cloud_Decorator_Tag的实例

---

试着这样做：

 $cloud = new Zend_Tag_Cloud(
    array(
        'tags' => array(
            array('title' => 'Code', 'weight' => 50),
            array('title' => 'Zend Framework', 'weight' => 100),
            array('title' => 'PHP', 'weight' => 25)
        ),
        'tagDecorator' => array(
            'decorator' => 'HtmlTag',
            'options' => array(
                'htmlTags' => array(),
                'fontSizeUnit' => 'px',
                'minFontSize' => 20
            )
        )
    )
);

 $cloud = new Zend_Tag_Cloud(
    array(
        'tags' => array(
            array('title' => 'Code', 'weight' => 50),
            array('title' => 'Zend Framework', 'weight' => 100),
            array('title' => 'PHP', 'weight' => 25)
        ),
        'tagDecorator' => array(
            'decorator' => 'HtmlTag',
            'options' => array(
                'htmlTags' => array(),
                'fontSizeUnit' => 'px',
                'minFontSize' => 20
            )
        )
    )
);