The subscription resource is used to define a push-based subscription from a server to another system. Once a subscription is registered with the server, the server checks every resource that is created or updated, and if the resource matches the given criteria, it sends a message on the defined "channel" so that another system can take an appropriate action. 订阅型resource用于定义用于记录推送到另一个服务端相关的信息. 订阅型resource一旦生成，在对应的resource有生成或修改满足订阅型资源所描述的，将会通过一种方式推送消息到被推送端，被推送端将会这些推送的信息作相应的业务操作。

The status of the subscription, which marks the server state for managing the subscription. 订阅型resource的状态，这个状态标记当前推送端管理订阅型resource的状态。

A client can only submit subscription resources in the requested or off state. Only the server can move a subscription from requested to active, and then to error. Either the server or the client can turn a subscription off. 客户端提交的订阅型resource的status的值只能为requested或off，只有fhir服务端可以将订阅型resource的状态从requested改为active或者error，无效是客户端还是fhir服务端都可 把status的值改为off.

This element is labeled as a modifier because the status contains codes that mark the resource as not currently valid. status不可或缺是因为其值标记着当前资源是否有效。

Contact details for a human to contact about the subscription. The primary use of this for system administrator troubleshooting. contact元素用于订阅型资源对人类可用的联系方式的描述，主要用途在于系统管理员解决问题时(需要找相关负责人)用到。

The time for the server to turn the subscription off. fhir服务端将订阅型资源的status修改为off时的时间。

The server is permitted to deviate from this time but should observe it. fhir服务端可以不用填写但最好填上。

A description of why this subscription is defined.这个订阅型resource存在的原因。

The rules that the server should use to determine when to generate notifications for this subscription. fhir服务端推送消息到被推送端的规则。

The rules are search criteria (without the [base] part). Like Bundle.entry.request.url, it has no leading "/". 这些规则为搜索条件（不需要带上基地址）就像Bundle.entry.request.url，不需要以“/”开头。

A record of the last error that occurred when the server processed a notification. 记录上次推送通知时的错误。

Details where to send notifications when resources are received that meet the criteria. 当满足条件时，要使用的推送方式。

The type of channel to send notifications on. 要使用的推送方式的类型。

The url that describes the actual end-point to send messages to. 推送通知使用的接入点。

For rest-hook, and websocket, the end-point must be an http: or https: URL; for email, a mailto: url, for sms, a tel: url, and for message the endpoint can be in any form of url the server understands (usually, http: or mllp:). The URI is allowed to be relative; in which case, it is relative to the server end-point (since there may be more than one, clients should avoid using relative URIs). 对于rest-hook和websocket方式，接入点的格式必须为http:url或https:url,对于email来说格式为mailto:url，对于短信来说为 tel:url，对于用message方式， 格式任意只要fhir服务端明白即可。（一般来说，为http:或mllp:开头）。URI可以是相对地址，这种情况下，它是相对fhir服务而言（为了不必要的麻烦，客户端最好避免使用相对URI）

The mime type to send the payload in - either application/fhir+xml, or application/fhir+json. If the payload is not present, then there is no payload in the notification, just a notification. The mime type "text/plain" may also be used for Email and SMS subscriptions. 内容的多媒体类型，可以是application/fhir+xml或application/fhir+json。如果payload元素没有那么意味着在通知里无内容，只是一个通知而已。 "text/plain"也可以用于email或sms的内容格式。

Sending the payload has obvious security implications. The server is responsible for ensuring that the content is appropriately secured. 直接发内容有安全隐患，推送端应该通过适当的方式加密数据。

Additional headers / information to send as part of the notification. 作为通知的额外header信息。

Exactly what these mean depend on the channel type. They can convey additional information to the recipient and/or meet security requirements; for example, support of multiple headers in the outgoing notifications for rest-hook type subscriptions. 根据实际的推送方式不同header的内容不同。header可用于给被推送端的额外信息或者用于满足一些安全需要。比如说，对于rest-hook方式的推送（根据实际情况）可以加入多种不同的header.