Plan-execute on Where ten HTTP header fields are defined

All 10 fields come from four RFCs: RFC 9111, RFC 9110, RFC 6797 and RFC 8288. I took each section number from the heading in the body of the RFC, not the table of contents, and each quote from the text under that heading.

One check didn't work. The plan was to confirm on the RFC Editor "info" pages that none of these RFCs has been obsoleted. Those pages returned 404, and the Datatracker links loaded the plain RFC text, which doesn't show status. Instead I ran three searches: one for RFC 9111 and one each for RFC 6797 and RFC 8288. None of them turned up a replacement RFC. That supports the answers below but doesn't prove them.

HTTP caching: RFC 9111 (https://www.rfc-editor.org/rfc/rfc9111.html). Its header says "Obsoletes: 7234", and it replaces RFC 7234, the older caching RFC.

• Age: section 5.1
• Cache-Control: section 5.2
• Expires: section 5.3

HTTP semantics: RFC 9110 (https://www.rfc-editor.org/rfc/rfc9110.html). It obsoletes RFCs 7231, 7232, 7233, 7235 and others, so those older RFCs weren't used.

• Last-Modified: section 8.8.2
• ETag: section 8.8.3
• Location: section 10.2.2
• Retry-After: section 10.2.3
• Vary: section 12.5.5

Strict-Transport-Security: RFC 6797, section 6.1 (https://www.rfc-editor.org/rfc/rfc6797.html). The RFC's header doesn't list it as obsoleting anything.

Link: RFC 8288, section 3 (https://www.rfc-editor.org/rfc/rfc8288.html). It obsoletes RFC 5988, the earlier Link RFC. Section 3 is titled "Link Serialisation in HTTP Headers". The RFC uses British spelling, so the quote has "serialising" where the plan expected "serializing".

Quotes: some sentences run across several lines on the page. In those quotes I joined the lines with single spaces, which is how the pages' search results showed the text.

{"answers":[
{"field":"Age","rfc":"9111","section":"5.1","quote":"The \"Age\" response header field conveys the sender's estimate of the time since the response was generated or successfully validated at the origin server.","url":"https://www.rfc-editor.org/rfc/rfc9111.html"},
{"field":"Cache-Control","rfc":"9111","section":"5.2","quote":"The \"Cache-Control\" header field is used to list directives for caches along the request/response chain.","url":"https://www.rfc-editor.org/rfc/rfc9111.html"},
{"field":"Expires","rfc":"9111","section":"5.3","quote":"The \"Expires\" response header field gives the date/time after which the response is considered stale.","url":"https://www.rfc-editor.org/rfc/rfc9111.html"},
{"field":"Last-Modified","rfc":"9110","section":"8.8.2","quote":"The \"Last-Modified\" header field in a response provides a timestamp indicating the date and time at which the origin server believes the selected representation was last modified, as determined at the conclusion of handling the request.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},
{"field":"ETag","rfc":"9110","section":"8.8.3","quote":"An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},
{"field":"Location","rfc":"9110","section":"10.2.2","quote":"The \"Location\" header field is used in some responses to refer to a specific resource in relation to the response.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},
{"field":"Retry-After","rfc":"9110","section":"10.2.3","quote":"Servers send the \"Retry-After\" header field to indicate how long the user agent ought to wait before making a follow-up request.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},
{"field":"Vary","rfc":"9110","section":"12.5.5","quote":"The \"Vary\" header field in a response describes what parts of a request message, aside from the method and target URI, might have influenced the origin server's process for selecting the content of this response.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},
{"field":"Strict-Transport-Security","rfc":"6797","section":"6.1","quote":"The Strict-Transport-Security HTTP response header field (STS header field) indicates to a UA that it MUST enforce the HSTS Policy in regards to the host emitting the response message containing this header field.","url":"https://www.rfc-editor.org/rfc/rfc6797.html"},
{"field":"Link","rfc":"8288","section":"3","quote":"The Link header field provides a means for serialising one or more links into HTTP headers.","url":"https://www.rfc-editor.org/rfc/rfc8288.html"}
]}