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<!DOCTYPE html>
<html lang="en">
<head>
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<title>HTTP Caching</title><script>
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<link rel="Contents" href="#rfc.toc">
<link rel="Author" href="#rfc.authors">
<link rel="License" href="#rfc.copyrightnotice">
<link rel="Index" href="#rfc.index">
<link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
<link rel="Chapter" title="2 Overview of Cache Operation" href="#rfc.section.2">
<link rel="Chapter" title="3 Storing Responses in Caches" href="#rfc.section.3">
<link rel="Chapter" title="4 Constructing Responses from Caches" href="#rfc.section.4">
<link rel="Chapter" title="5 Field Definitions" href="#rfc.section.5">
<link rel="Chapter" title="6 Relationship to Applications and Other Caches" href="#rfc.section.6">
<link rel="Chapter" title="7 Security Considerations" href="#rfc.section.7">
<link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8">
<link rel="Chapter" title="9 References" href="#rfc.section.9">
<link rel="Appendix" title="A Collected ABNF" href="#rfc.section.A">
<link rel="Appendix" title="B Changes from RFC 7234" href="#rfc.section.B">
<link rel="Appendix" title="C Change Log" href="#rfc.section.C">
<link rel="Appendix" title="Acknowledgements" href="#rfc.section.unnumbered-1">
<meta name="viewport" content="initial-scale=1">
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<meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP Caching">
<link rel="schema.dcterms" href="http://purl.org/dc/terms/">
<meta name="dcterms.creator" content="Fielding, R.">
<meta name="dcterms.creator" content="Nottingham, M.">
<meta name="dcterms.creator" content="Reschke, J.">
<meta name="dcterms.issued" content="2022-11-01">
<meta name="dct.replaces" content="urn:ietf:rfc:7234">
<meta name="dcterms.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234.">
<meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234.">
</head>
<body onload="initFeedback();">
<header>
<table class="header" id="rfc.headerblock">
<tbody>
<tr>
<td class="left"><a href="https://datatracker.ietf.org/wg/httpbis">HTTP Working Group</a></td>
<td class="right">R. Fielding, Editor</td>
</tr>
<tr>
<td class="left">Internet-Draft</td>
<td class="right">Adobe</td>
</tr>
<tr>
<td class="left">Obsoletes: <a href="#RFC7234">7234</a> (if approved)</td>
<td class="right">M. Nottingham, Editor</td>
</tr>
<tr>
<td class="left">Intended status: Standards Track</td>
<td class="right">Fastly</td>
</tr>
<tr>
<td class="left">Expires: May 5, 2023</td>
<td class="right">J. Reschke, Editor</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">greenbytes</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">November 1, 2022</td>
</tr>
</tbody>
</table>
<div id="rfc.title">
<h1>HTTP Caching</h1>
<div class="filename"><a href="https://datatracker.ietf.org/doc/draft-ietf-httpbis-cache" class="smpl">draft-ietf-httpbis-cache-latest</a></div>
</div>
</header>
<section>
<h2 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h2>
<div id="rfc.abstract.p.1">
<p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for
distributed, collaborative, hypertext information systems. This document defines HTTP
caches and the associated header fields that control cache behavior or indicate cacheable
response messages.<a class="self" href="#rfc.abstract.p.1">¶</a></p>
</div>
<div id="rfc.abstract.p.2">
<p>This document obsoletes RFC 7234.<a class="self" href="#rfc.abstract.p.2">¶</a></p>
</div>
</section>
<section class="note rfcEditorRemove">
<h2 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note</a></h2>
<div id="rfc.note.1.p.1">
<p>This note is to be removed before publishing as an RFC.<a class="self" href="#rfc.note.1.p.1">¶</a></p>
</div>
<div id="rfc.note.1.p.2">
<p>Discussion of this draft takes place on the HTTP working group mailing list (ietf-http-wg@w3.org),
which is archived at <a href="https://lists.w3.org/Archives/Public/ietf-http-wg/">https://lists.w3.org/Archives/Public/ietf-http-wg/</a>.<a class="self" href="#rfc.note.1.p.2">¶</a></p>
</div>
<div id="rfc.note.1.p.3">
<p>Working Group information can be found at <a href="https://httpwg.org/">https://httpwg.org/</a>; source code and issues list for this draft can be found at <a href="https://github.com/httpwg/http-core">https://github.com/httpwg/http-core</a>.<a class="self" href="#rfc.note.1.p.3">¶</a></p>
</div>
<div id="rfc.note.1.p.4">
<p>The changes in this draft are summarized in <a href="#changes.since.19" title="Since draft-ietf-httpbis-cache-19">Appendix C.1</a>.<a class="self" href="#rfc.note.1.p.4">¶</a></p>
</div>
</section>
<section id="rfc.status">
<h2><a href="#rfc.status">Status of This Memo</a></h2>
<div id="rfc.boilerplate.1.p.1">
<p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78
and BCP 79.<a class="self" href="#rfc.boilerplate.1.p.1">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.2">
<p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF).
Note that other groups may also distribute working documents as Internet-Drafts. The
list of current Internet-Drafts is at <a href="https://datatracker.ietf.org/drafts/current/">https://datatracker.ietf.org/drafts/current/</a>.<a class="self" href="#rfc.boilerplate.1.p.2">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.3">
<p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated,
replaced, or obsoleted by other documents at any time. It is inappropriate to use
Internet-Drafts as reference material or to cite them other than as “work in progress”.<a class="self" href="#rfc.boilerplate.1.p.3">¶</a></p>
</div>
<div id="rfc.boilerplate.1.p.4">
<p>This Internet-Draft will expire on May 5, 2023.<a class="self" href="#rfc.boilerplate.1.p.4">¶</a></p>
</div>
</section>
<section id="rfc.copyrightnotice">
<h2><a href="#rfc.copyrightnotice">Copyright Notice</a></h2>
<div id="rfc.boilerplate.2.p.1">
<p>Copyright (c) 2022 IETF Trust and the persons identified as the document authors.
All rights reserved.<a class="self" href="#rfc.boilerplate.2.p.1">¶</a></p>
</div>
<div id="rfc.boilerplate.2.p.2">
<p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating
to IETF Documents (<a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect to this document.
Code Components extracted from this document must include Revised BSD License text
as described in Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Revised BSD License.<a class="self" href="#rfc.boilerplate.2.p.2">¶</a></p>
</div>
<div id="rfc.boilerplate.2.p.3">
<p>This document may contain material from IETF Documents or IETF Contributions published
or made publicly available before November 10, 2008. The person(s) controlling the
copyright in some of this material may not have granted the IETF Trust the right to
allow modifications of such material outside the IETF Standards Process. Without obtaining
an adequate license from the person(s) controlling the copyright in such materials,
this document may not be modified outside the IETF Standards Process, and derivative
works of it may not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other than English.<a class="self" href="#rfc.boilerplate.2.p.3">¶</a></p>
</div>
</section>
<hr class="noprint">
<nav id="rfc.toc">
<h2 class="np"><a href="#rfc.toc">Table of Contents</a></h2>
<ul class="toc">
<li><a href="#rfc.section.1">1.</a> <a href="#caching">Introduction</a><ul>
<li><a href="#rfc.section.1.1">1.1.</a> <a href="#requirements.notation">Requirements Notation</a></li>
<li><a href="#rfc.section.1.2">1.2.</a> <a href="#notation">Syntax Notation</a><ul>
<li><a href="#rfc.section.1.2.1">1.2.1.</a> <a href="#abnf.imported">Imported Rules</a></li>
<li><a href="#rfc.section.1.2.2">1.2.2.</a> <a href="#delta-seconds">Delta Seconds</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#rfc.section.2">2.</a> <a href="#caching.overview">Overview of Cache Operation</a></li>
<li><a href="#rfc.section.3">3.</a> <a href="#response.cacheability">Storing Responses in Caches</a><ul>
<li><a href="#rfc.section.3.1">3.1.</a> <a href="#storing.fields">Storing Header and Trailer Fields</a></li>
<li><a href="#rfc.section.3.2">3.2.</a> <a href="#update">Updating Stored Header Fields</a></li>
<li><a href="#rfc.section.3.3">3.3.</a> <a href="#incomplete.responses">Storing Incomplete Responses</a></li>
<li><a href="#rfc.section.3.4">3.4.</a> <a href="#combining.responses">Combining Partial Content</a></li>
<li><a href="#rfc.section.3.5">3.5.</a> <a href="#caching.authenticated.responses">Storing Responses to Authenticated Requests</a></li>
</ul>
</li>
<li><a href="#rfc.section.4">4.</a> <a href="#constructing.responses.from.caches">Constructing Responses from Caches</a><ul>
<li><a href="#rfc.section.4.1">4.1.</a> <a href="#caching.negotiated.responses">Calculating Cache Keys with the Vary Header Field</a></li>
<li><a href="#rfc.section.4.2">4.2.</a> <a href="#expiration.model">Freshness</a><ul>
<li><a href="#rfc.section.4.2.1">4.2.1.</a> <a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></li>
<li><a href="#rfc.section.4.2.2">4.2.2.</a> <a href="#heuristic.freshness">Calculating Heuristic Freshness</a></li>
<li><a href="#rfc.section.4.2.3">4.2.3.</a> <a href="#age.calculations">Calculating Age</a></li>
<li><a href="#rfc.section.4.2.4">4.2.4.</a> <a href="#serving.stale.responses">Serving Stale Responses</a></li>
</ul>
</li>
<li><a href="#rfc.section.4.3">4.3.</a> <a href="#validation.model">Validation</a><ul>
<li><a href="#rfc.section.4.3.1">4.3.1.</a> <a href="#validation.sent">Sending a Validation Request</a></li>
<li><a href="#rfc.section.4.3.2">4.3.2.</a> <a href="#validation.received">Handling a Received Validation Request</a></li>
<li><a href="#rfc.section.4.3.3">4.3.3.</a> <a href="#validation.response">Handling a Validation Response</a></li>
<li><a href="#rfc.section.4.3.4">4.3.4.</a> <a href="#freshening.responses">Freshening Stored Responses upon Validation</a></li>
<li><a href="#rfc.section.4.3.5">4.3.5.</a> <a href="#head.effects">Freshening Responses with HEAD</a></li>
</ul>
</li>
<li><a href="#rfc.section.4.4">4.4.</a> <a href="#invalidation">Invalidating Stored Responses</a></li>
</ul>
</li>
<li><a href="#rfc.section.5">5.</a> <a href="#header.field.definitions">Field Definitions</a><ul>
<li><a href="#rfc.section.5.1">5.1.</a> <a href="#field.age">Age</a></li>
<li><a href="#rfc.section.5.2">5.2.</a> <a href="#field.cache-control">Cache-Control</a><ul>
<li><a href="#rfc.section.5.2.1">5.2.1.</a> <a href="#cache-request-directive">Request Directives</a><ul>
<li><a href="#rfc.section.5.2.1.1">5.2.1.1.</a> <a href="#cache-request-directive.max-age">max-age</a></li>
<li><a href="#rfc.section.5.2.1.2">5.2.1.2.</a> <a href="#cache-request-directive.max-stale">max-stale</a></li>
<li><a href="#rfc.section.5.2.1.3">5.2.1.3.</a> <a href="#cache-request-directive.min-fresh">min-fresh</a></li>
<li><a href="#rfc.section.5.2.1.4">5.2.1.4.</a> <a href="#cache-request-directive.no-cache">no-cache</a></li>
<li><a href="#rfc.section.5.2.1.5">5.2.1.5.</a> <a href="#cache-request-directive.no-store">no-store</a></li>
<li><a href="#rfc.section.5.2.1.6">5.2.1.6.</a> <a href="#cache-request-directive.no-transform">no-transform</a></li>
<li><a href="#rfc.section.5.2.1.7">5.2.1.7.</a> <a href="#cache-request-directive.only-if-cached">only-if-cached</a></li>
</ul>
</li>
<li><a href="#rfc.section.5.2.2">5.2.2.</a> <a href="#cache-response-directive">Response Directives</a><ul>
<li><a href="#rfc.section.5.2.2.1">5.2.2.1.</a> <a href="#cache-response-directive.max-age">max-age</a></li>
<li><a href="#rfc.section.5.2.2.2">5.2.2.2.</a> <a href="#cache-response-directive.must-revalidate">must-revalidate</a></li>
<li><a href="#rfc.section.5.2.2.3">5.2.2.3.</a> <a href="#cache-response-directive.must-understand">must-understand</a></li>
<li><a href="#rfc.section.5.2.2.4">5.2.2.4.</a> <a href="#cache-response-directive.no-cache">no-cache</a></li>
<li><a href="#rfc.section.5.2.2.5">5.2.2.5.</a> <a href="#cache-response-directive.no-store">no-store</a></li>
<li><a href="#rfc.section.5.2.2.6">5.2.2.6.</a> <a href="#cache-response-directive.no-transform">no-transform</a></li>
<li><a href="#rfc.section.5.2.2.7">5.2.2.7.</a> <a href="#cache-response-directive.private">private</a></li>
<li><a href="#rfc.section.5.2.2.8">5.2.2.8.</a> <a href="#cache-response-directive.proxy-revalidate">proxy-revalidate</a></li>
<li><a href="#rfc.section.5.2.2.9">5.2.2.9.</a> <a href="#cache-response-directive.public">public</a></li>
<li><a href="#rfc.section.5.2.2.10">5.2.2.10.</a> <a href="#cache-response-directive.s-maxage">s-maxage</a></li>
</ul>
</li>
<li><a href="#rfc.section.5.2.3">5.2.3.</a> <a href="#cache.control.extensions">Extension Directives</a></li>
<li><a href="#rfc.section.5.2.4">5.2.4.</a> <a href="#cache.directive.registry">Cache Directive Registry</a></li>
</ul>
</li>
<li><a href="#rfc.section.5.3">5.3.</a> <a href="#field.expires">Expires</a></li>
<li><a href="#rfc.section.5.4">5.4.</a> <a href="#field.pragma">Pragma</a></li>
<li><a href="#rfc.section.5.5">5.5.</a> <a href="#field.warning">Warning</a></li>
</ul>
</li>
<li><a href="#rfc.section.6">6.</a> <a href="#history.lists">Relationship to Applications and Other Caches</a></li>
<li><a href="#rfc.section.7">7.</a> <a href="#security.considerations">Security Considerations</a><ul>
<li><a href="#rfc.section.7.1">7.1.</a> <a href="#cache.poisoning">Cache Poisoning</a></li>
<li><a href="#rfc.section.7.2">7.2.</a> <a href="#security.timing">Timing Attacks</a></li>
<li><a href="#rfc.section.7.3">7.3.</a> <a href="#caching.of.sensitive.information">Caching of Sensitive Information</a></li>
</ul>
</li>
<li><a href="#rfc.section.8">8.</a> <a href="#iana.considerations">IANA Considerations</a><ul>
<li><a href="#rfc.section.8.1">8.1.</a> <a href="#field.name.registration">Field Name Registration</a></li>
<li><a href="#rfc.section.8.2">8.2.</a> <a href="#cache.directive.registration">Cache Directive Registration</a></li>
<li><a href="#rfc.section.8.3">8.3.</a> <a href="#warn.code.registration">Warn Code Registry</a></li>
</ul>
</li>
<li><a href="#rfc.section.9">9.</a> <a href="#rfc.references">References</a><ul>
<li><a href="#rfc.section.9.1">9.1.</a> <a href="#rfc.references.1">Normative References</a></li>
<li><a href="#rfc.section.9.2">9.2.</a> <a href="#rfc.references.2">Informative References</a></li>
</ul>
</li>
<li><a href="#rfc.section.A">Appendix A.</a> <a href="#collected.abnf">Collected ABNF</a></li>
<li><a href="#rfc.section.B">Appendix B.</a> <a href="#changes.from.rfc.7234">Changes from RFC 7234</a></li>
<li><a href="#rfc.section.C">Appendix C.</a> <a href="#change.log">Change Log</a><ul>
<li><a href="#rfc.section.C.1">C.1.</a> <a href="#changes.since.19">Since draft-ietf-httpbis-cache-19</a></li>
</ul>
</li>
<li><a href="#acks">Acknowledgements</a></li>
<li><a href="#rfc.index">Index</a></li>
<li><a href="#rfc.authors">Authors' Addresses</a></li>
</ul>
</nav>
<section id="caching">
<h2 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a href="#caching">Introduction</a></h2>
<div id="rfc.section.1.p.1">
<p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level request/response
protocol that uses extensible semantics and self-descriptive messages for flexible
interaction with network-based hypertext information systems. It is typically used
for distributed information systems, where the use of response caches can improve
performance. This document defines aspects of HTTP related to caching and reusing
response messages.<a class="self" href="#rfc.section.1.p.1">¶</a></p>
</div>
<div id="rfc.iref.c.1"></div>
<div id="rfc.section.1.p.2">
<p>An HTTP <dfn>cache</dfn> is a local store of response messages and the subsystem that controls storage, retrieval,
and deletion of messages in it. A cache stores cacheable responses to reduce the response
time and network bandwidth consumption on future equivalent requests. Any client or
server <em class="bcp14">MAY</em> use a cache, though not when acting as a tunnel (<a href="draft-ietf-httpbis-semantics-latest.html#intermediaries" title="Intermediaries">Section 3.7</a> of <a href="#HTTP" id="rfc.xref.HTTP.1"><cite title="HTTP Semantics">[HTTP]</cite></a>).<a class="self" href="#rfc.section.1.p.2">¶</a></p>
</div>
<div id="rfc.iref.s.1"></div>
<div id="rfc.iref.p.1"></div>
<div id="rfc.section.1.p.3">
<p id="shared.and.private.caches">A <dfn>shared cache</dfn> is a cache that stores responses for reuse by more than one user; shared caches are
usually (but not always) deployed as a part of an intermediary. A <dfn>private cache</dfn>, in contrast, is dedicated to a single user; often, they are deployed as a component
of a user agent.<a class="self" href="#rfc.section.1.p.3">¶</a></p>
</div>
<div id="rfc.section.1.p.4">
<p>The goal of HTTP caching is significantly improving performance by reusing a prior
response message to satisfy a current request. A cache considers a stored response
"fresh", as defined in <a href="#expiration.model" title="Freshness">Section 4.2</a>, if it can be reused without "validation" (checking with the origin server to see
if the cached response remains valid for this request). A fresh response can therefore
reduce both latency and network overhead each time the cache reuses it. When a cached
response is not fresh, it might still be reusable if validation can freshen it (<a href="#validation.model" title="Validation">Section 4.3</a>) or if the origin is unavailable (<a href="#serving.stale.responses" title="Serving Stale Responses">Section 4.2.4</a>).<a class="self" href="#rfc.section.1.p.4">¶</a></p>
</div>
<div id="rfc.section.1.p.5">
<p>This document obsoletes <a href="#RFC7234" id="rfc.xref.RFC7234.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">RFC 7234</cite></a>, with the changes being summarized in <a href="#changes.from.rfc.7234" title="Changes from RFC 7234">Appendix B</a>.<a class="self" href="#rfc.section.1.p.5">¶</a></p>
</div>
<section id="requirements.notation">
<h3 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1.</a> <a href="#requirements.notation">Requirements Notation</a></h3>
<div id="rfc.section.1.1.p.1">
<p>The key words "<em class="bcp14">MUST</em>", "<em class="bcp14">MUST NOT</em>", "<em class="bcp14">REQUIRED</em>", "<em class="bcp14">SHALL</em>", "<em class="bcp14">SHALL NOT</em>", "<em class="bcp14">SHOULD</em>", "<em class="bcp14">SHOULD NOT</em>", "<em class="bcp14">RECOMMENDED</em>", "<em class="bcp14">NOT RECOMMENDED</em>", "<em class="bcp14">MAY</em>", and "<em class="bcp14">OPTIONAL</em>" in this document are to be interpreted as described in BCP 14 <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a> <a href="#RFC8174" id="rfc.xref.RFC8174.1"><cite title="Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words">[RFC8174]</cite></a> when, and only when, they appear in all capitals, as shown here.<a class="self" href="#rfc.section.1.1.p.1">¶</a></p>
</div>
<div id="rfc.section.1.1.p.2">
<p><a href="draft-ietf-httpbis-semantics-latest.html#conformance" title="Conformance">Section 2</a> of <a href="#HTTP" id="rfc.xref.HTTP.2"><cite title="HTTP Semantics">[HTTP]</cite></a> defines conformance criteria and contains considerations regarding error handling.<a class="self" href="#rfc.section.1.1.p.2">¶</a></p>
</div>
</section>
<section id="notation">
<h3 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2.</a> <a href="#notation">Syntax Notation</a></h3>
<div id="rfc.section.1.2.p.1">
<p>This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, extended with the notation for case-sensitivity in strings defined in <a href="#RFC7405" id="rfc.xref.RFC7405.1"><cite title="Case-Sensitive String Support in ABNF">[RFC7405]</cite></a>.<a class="self" href="#rfc.section.1.2.p.1">¶</a></p>
</div>
<div id="rfc.section.1.2.p.2">
<p>It also uses a list extension, defined in <a href="draft-ietf-httpbis-semantics-latest.html#abnf.extension" title="Lists (#rule ABNF Extension)">Section 5.6.1</a> of <a href="#HTTP" id="rfc.xref.HTTP.3"><cite title="HTTP Semantics">[HTTP]</cite></a>, that allows for compact definition of comma-separated lists using a "#" operator
(similar to how the "*" operator indicates repetition). <a href="#collected.abnf" title="Collected ABNF">Appendix A</a> shows the collected grammar with all list operators expanded to standard ABNF notation.<a class="self" href="#rfc.section.1.2.p.2">¶</a></p>
</div>
<section id="abnf.imported">
<h4 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1.</a> <a href="#abnf.imported">Imported Rules</a></h4>
<div id="rfc.section.1.2.1.p.1">
<p id="core.rules">The following core rule is included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="https://www.rfc-editor.org/rfc/rfc5234.html#appendix-B.1">Appendix B.1</a>: DIGIT (decimal 0-9).<a class="self" href="#rfc.section.1.2.1.p.1">¶</a></p>
</div>
<div id="rfc.section.1.2.1.p.2" class="avoidbreakafter">
<p id="imported.rules"><a href="#HTTP" id="rfc.xref.HTTP.4"><cite title="HTTP Semantics">[HTTP]</cite></a> defines the following rules:<a class="self" href="#rfc.section.1.2.1.p.2">¶</a></p>
</div>
<div id="rfc.section.1.2.1.p.3">
<pre class="inline prettyprint lang-ietf_abnf"> <a href="#imported.rules" class="smpl">HTTP-date</a> = <HTTP-date, see <a href="#HTTP" id="rfc.xref.HTTP.5"><cite title="HTTP Semantics">[HTTP]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#http.date" title="Date/Time Formats">Section 5.6.7</a>>
<a href="#imported.rules" class="smpl">OWS</a> = <OWS, see <a href="#HTTP" id="rfc.xref.HTTP.6"><cite title="HTTP Semantics">[HTTP]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#whitespace" title="Whitespace">Section 5.6.3</a>>
<a href="#imported.rules" class="smpl">field-name</a> = <field-name, see <a href="#HTTP" id="rfc.xref.HTTP.7"><cite title="HTTP Semantics">[HTTP]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#fields.names" title="Field Names">Section 5.1</a>>
<a href="#imported.rules" class="smpl">quoted-string</a> = <quoted-string, see <a href="#HTTP" id="rfc.xref.HTTP.8"><cite title="HTTP Semantics">[HTTP]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#quoted.strings" title="Quoted Strings">Section 5.6.4</a>>
<a href="#imported.rules" class="smpl">token</a> = <token, see <a href="#HTTP" id="rfc.xref.HTTP.9"><cite title="HTTP Semantics">[HTTP]</cite></a>, <a href="draft-ietf-httpbis-semantics-latest.html#tokens" title="Tokens">Section 5.6.2</a>>
</pre>
</div>
</section>
<section id="delta-seconds">
<h4 id="rfc.section.1.2.2"><a href="#rfc.section.1.2.2">1.2.2.</a> <a href="#delta-seconds">Delta Seconds</a></h4>
<div id="rfc.section.1.2.2.p.1">
<p>The delta-seconds rule specifies a non-negative integer, representing time in seconds.<a class="self" href="#rfc.section.1.2.2.p.1">¶</a></p>
</div>
<div id="rfc.section.1.2.2.p.2">
<pre class="inline prettyprint lang-ietf_abnf"><span id="rfc.iref.g.1"></span> <a href="#delta-seconds" class="smpl">delta-seconds</a> = 1*<a href="#core.rules" class="smpl">DIGIT</a>
</pre>
</div>
<div id="rfc.section.1.2.2.p.3">