(Yaf >=1.0.0)
Yaf_Response_Abstract::clearBody — 清除已经设置的响应body
$key = ?
) : bool清除已经设置的响应body
keythe content key, if you don't specific, then all contents will be cleared. 如果你没选择具体清除哪个key所对应的内容，那所有内容将被清除
注意:
this parameter is introduced as of 2.2.0