如果请求没有包含完成身份验证事务所需的足够信息，身份验证提供者会使用前面提到的回调功能。
If a request doesn't contain enough information to complete the authentication transaction right now the authentication provider will use the call-back functionality mentioned earlier.
属性回调是为组件属性注册相同属性类型信息的一项功能。
The property callback is a function that registers the same property type information for the component properties.
回调可为发布程序提供增强的功能性，这与我们的另一篇文章中所描述的客户机订阅类似。
Similar to the subscribing clients described in our other article, callbacks provide enhanced functionality for publishers.
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