页面：

<open-data class="userHeadPicture" type="userAvatarUrl"></open-data>

js：

console.log(wx.canIUse('open-data'));    //true

console.log(wx.canIUse('open-data.userAvatarUrl'));    //false

为什么'open-data'为true,'open-data.userAvatarUrl'为false呢？