Plan-execute on Where ten HTTP header fields are defined

All ten header fields are defined in four RFCs. None of the four pages I opened shows an "Obsoleted by" notice. I searched each page for that phrase. RFC 9110 matched only in its own "Specifications Obsoleted by This Document" section, and the other three pages had no match. I did not check an external index such as the RFC Editor's info page.

• RFC 9111 (HTTP Caching) defines Age (5.1), Cache-Control (5.2) and Expires (5.3). It is at https://www.rfc-editor.org/rfc/rfc9111.html.
• RFC 9110 (HTTP Semantics) defines Last-Modified (8.8.2), ETag (8.8.3), Location (10.2.2), Retry-After (10.2.3) and Vary (12.5.5). It is at https://www.rfc-editor.org/rfc/rfc9110.html.
• RFC 6797 defines Strict-Transport-Security in section 6.1. It is at https://www.rfc-editor.org/rfc/rfc6797.html.
• RFC 8288 defines Link in section 3. It is at https://www.rfc-editor.org/rfc/rfc8288.html.

I did not open RFC 7231, 7232, 7234 or 5988. I did not confirm from the pages that 9110, 9111 and 8288 replace them. That comes from my own recollection. I left those RFCs out of the answer.

Where the plan relied on memory for section numbers, I took them from the section headings on the pages I opened. They matched. The sources did not disagree on anything.

{"answers":[{"field":"Age","rfc":"9111","section":"5.1","quote":"The Age field value is a non-negative integer, representing time in seconds (see Section 1.2.2).","url":"https://www.rfc-editor.org/rfc/rfc9111.html"},{"field":"Cache-Control","rfc":"9111","section":"5.2","quote":"It is not possible to target a directive to a specific cache.","url":"https://www.rfc-editor.org/rfc/rfc9111.html"},{"field":"Expires","rfc":"9111","section":"5.3","quote":"The presence of an Expires header field does not imply that the original resource will change or cease to exist at, before, or after that time.","url":"https://www.rfc-editor.org/rfc/rfc9111.html"},{"field":"Last-Modified","rfc":"9110","section":"8.8.2","quote":"An example of its use is","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 field value consists of a single URI-reference.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"field":"Retry-After","rfc":"9110","section":"10.2.3","quote":"The Retry-After field value can be either an HTTP-date or a number of seconds to delay after receiving the response.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"field":"Vary","rfc":"9110","section":"12.5.5","quote":"A proxy MUST NOT generate \"*\" in a Vary field value.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"field":"Strict-Transport-Security","rfc":"6797","section":"6.1","quote":"The order of appearance of directives is not significant.","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"}]}

The Last-Modified quote, "An example of its use is", is only five words, below the six-word minimum. I should have used the longer sentence from the same section. It reads: "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." Use that in place of the short one, escaping the inner double quotes as \".