Plan-execute-verify on Where ten HTTP header fields are defined

All ten fields are defined in four RFCs. For each one I opened the RFC on rfc-editor.org, took the section number from the heading on the page, and copied a sentence from that section.

RFC 9111 (HTTP Caching) – https://www.rfc-editor.org/rfc/rfc9111.html

• Its header says "Obsoletes: 7234".
• Age is in section 5.1, Cache-Control in 5.2 and Expires in 5.3.
• RFC 9111's own IANA registration table gives the same sections for Age (5.1) and Cache-Control (5.2).

RFC 9110 (HTTP Semantics) – https://www.rfc-editor.org/rfc/rfc9110.html

• Its header says "Obsoletes: 2818, 7230, 7231, 7232, 7233, 7235, 7538, 7615, 7694".
• Last-Modified is in section 8.8.2 and ETag in 8.8.3.
• Location is in section 10.2.2 and Retry-After in 10.2.3.
• Vary is in section 12.5.5.

RFC 6797 (HSTS) – https://www.rfc-editor.org/rfc/rfc6797.html

• Strict-Transport-Security is in section 6.1, "Strict-Transport-Security HTTP Response Header Field".

RFC 8288 (Web Linking) – https://www.rfc-editor.org/rfc/rfc8288.html

• Its header says "Obsoletes: 5988".
• Link is in section 3, "Link Serialisation in HTTP Headers". That section begins "The Link header field provides a means for serialising one or more links into HTTP headers."

What I couldn't confirm

• None of the four RFC pages shows an "Obsoleted by" line. However, an RFC's text isn't updated when a later RFC replaces it, so that alone doesn't prove the RFC is still current.

• I tried to confirm current status in two other places, and both returned "404 Not Found":

  • the RFC Editor status pages (https://www.rfc-editor.org/info/rfc6797 and the matching pages for 8288, 9110 and 9111)
  • the IANA field name registry (https://www.iana.org/assignments/http-fields/http-fields.xhtml)

  I can't cite those pages, so I couldn't cross-check the answers against IANA.

• Searches for a newer RFC replacing 6797 or 8288 found nothing. On the sources I could open, all four RFCs appear to be current, but that isn't fully confirmed.

About the quotes

• In the RFC pages, sentences wrap over several lines. I joined each sentence's lines with single spaces, so a check that compares whitespace exactly may not match.
• The ETag quote contains "W/" in double quotes, which are escaped as \" in the JSON.

{"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":"The \"ETag\" field in a response provides the current entity tag for the selected representation, as determined at the conclusion of handling the request.","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"}
]}