Single on Where ten HTTP header fields are defined

Perfect! Now I have all the information I need. Let me compile the final results with the exact quotes from the RFCs I've fetched.

Based on my research, here are the HTTP header field definitions from the current (non-obsoleted) RFCs:

Summary

I found that the current HTTP specifications are:

• RFC 9110 (HTTP Semantics) - defines Last-Modified, ETag, Location, Retry-After, and Vary
• RFC 9111 (HTTP Caching) - defines Age, Cache-Control, and Expires
• RFC 6797 (HTTP Strict Transport Security) - defines Strict-Transport-Security
• RFC 8288 (Web Linking) - defines Link

The older RFC 7231/7234 series have been obsoleted by RFC 9110/9111.

Here are my findings:

{"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.","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"}
]}