RFC 7234 - 5. Header Field Definitions (头字段定义)
This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.
This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.
User agents often have history mechanisms, such as "Back" buttons and history lists, that can be used to redisplay a representation retrieved earlier in a session.