Changeset 1251 for draft-ietf-httpbis


Ignore:
Timestamp:
31/03/11 12:11:25 (10 years ago)
Author:
fielding@…
Message:

editorial: rewrite introduction to p4 conditionals and compress some
the references to ABNF in other parts so that they don't impede the
readability of this part. Add informative ref to WebDAV spec.

Addresses #228

Location:
draft-ietf-httpbis/latest
Files:
2 edited

Legend:

Unmodified
Added
Removed

  • draft-ietf-httpbis/latest/p4-conditional.html

    r1243 r1251  
    359359  }
    360360  @bottom-center {
    361        content: "Expires October 1, 2011";
     361       content: "Expires October 2, 2011";
    362362  }
    363363  @bottom-right {
    … …  
    382382      <link rel="Index" href="#rfc.index">
    383383      <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
    384       <link rel="Chapter" title="2 Entity-Tags" href="#rfc.section.2">
     384      <link rel="Chapter" title="2 Resource State Metadata" href="#rfc.section.2">
    385385      <link rel="Chapter" title="3 Status Code Definitions" href="#rfc.section.3">
    386386      <link rel="Chapter" title="4 Weak and Strong Validators" href="#rfc.section.4">
    … …  
    406406      <meta name="dct.creator" content="Reschke, J. F.">
    407407      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p4-conditional-latest">
    408       <meta name="dct.issued" scheme="ISO8601" content="2011-03-30">
     408      <meta name="dct.issued" scheme="ISO8601" content="2011-03-31">
    409409      <meta name="dct.replaces" content="urn:ietf:rfc:2616">
    410410      <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 4 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those requests.">
    … …  
    432432            </tr>
    433433            <tr>
    434                <td class="left">Expires: October 1, 2011</td>
     434               <td class="left">Expires: October 2, 2011</td>
    435435               <td class="right">J. Mogul</td>
    436436            </tr>
    … …  
    489489            <tr>
    490490               <td class="left"></td>
    491                <td class="right">March 30, 2011</td>
     491               <td class="right">March 31, 2011</td>
    492492            </tr>
    493493         </tbody>
    … …  
    515515         in progress”.
    516516      </p>
    517       <p>This Internet-Draft will expire on October 1, 2011.</p>
     517      <p>This Internet-Draft will expire on October 2, 2011.</p>
    518518      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    519519      <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
    … …  
    535535         <li>1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
    536536               <li>1.1&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
    537                <li>1.2&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a><ul>
    538                      <li>1.2.1&nbsp;&nbsp;&nbsp;<a href="#core.rules">Core Rules</a></li>
    539                      <li>1.2.2&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
     537               <li>1.2&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li>
     538            </ul>
     539         </li>
     540         <li>2.&nbsp;&nbsp;&nbsp;<a href="#resource.metadata">Resource State Metadata</a><ul>
     541               <li>2.1&nbsp;&nbsp;&nbsp;<a href="#entity.tags">Entity Tags</a><ul>
     542                     <li>2.1.1&nbsp;&nbsp;&nbsp;<a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li>
    540543                  </ul>
    541544               </li>
    542             </ul>
    543          </li>
    544          <li>2.&nbsp;&nbsp;&nbsp;<a href="#entity.tags">Entity-Tags</a><ul>
    545                <li>2.1&nbsp;&nbsp;&nbsp;<a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li>
    546545            </ul>
    547546         </li>
    … …  
    598597      </ul>
    599598      <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
    600       <p id="rfc.section.1.p.1">This document defines HTTP/1.1 response metadata for indicating potential changes to payload content, including modification
    601          time stamps and opaque entity-tags, and the HTTP conditional request mechanisms that allow preconditions to be placed on a
    602          request method. Conditional GET requests allow for efficient cache updates. Other conditional request methods are used to
    603          protect against overwriting or misunderstanding the state of a resource that has been changed unbeknownst to the requesting
    604          client.
    605       </p>
    606       <p id="rfc.section.1.p.2"><span id="rfc.iref.s.1"></span> We use the term "<dfn>selected representation</dfn>" to refer to the current representation of the target resource that would have been selected and sent as payload in a 200
    607          (OK) response if the same request had used the method GET and had excluded all of the conditional request header fields. The
    608          conditions found within conditional requests are evaluated on the basis of either the state of the target resource as a whole
    609          or the state of the target resource's selected representation.
    610       </p>
    611       <p id="rfc.section.1.p.3">This document is currently disorganized in order to minimize the changes between drafts and enable reviewers to see the smaller
    612          errata changes. A future draft will reorganize the sections to better reflect the content. In particular, the sections on
    613          resource metadata will be discussed first and then followed by each conditional request header field, concluding with a definition
    614          of precedence and the expectation of ordering strong validator checks before weak validator checks. It is likely that more
    615          content from <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a> will migrate to this part, where appropriate. The current mess reflects how widely dispersed these topics and associated requirements
    616          had become in <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
     599      <p id="rfc.section.1.p.1">This document defines the HTTP/1.1 conditional request mechanisms, including both response metadata that can be used to indicate
     600         or observe changes to resource state and request header fields that specify preconditions to be checked before performing
     601         the action given by the request method. Conditional GET requests are the most efficient mechanism for HTTP cache updates.
     602         Conditionals can be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem: one client
     603         accidentally overwriting the work of another client that has been acting in parallel.
     604      </p>
     605      <p id="rfc.section.1.p.2">Conditional request preconditions are based on the state of the target resource as a whole (its current value set) or the
     606         state as observed in a previously obtained representation (one value in that set). A resource might have multiple current
     607         representations, each with its own observable state. The conditional request mechanisms assume that the mapping of requests
     608         to corresponding representations will be consistent over time if the server intends to take advantage of conditionals. Regardless,
     609         if the mapping is inconsistent and the server is unable to select the appropriate representation, then no harm will result
     610         when the precondition evaluates to false.
     611      </p>
     612      <p id="rfc.section.1.p.3"><span id="rfc.iref.s.1"></span> We use the term "<dfn>selected representation</dfn>" to refer to the current representation of the target resource that would have been selected in a successful response if
     613         the same request had used the method GET and had excluded all of the conditional request header fields. The conditional request
     614         preconditions are evaluated by comparing the values provided in the request header fields to the current metadata for the
     615         selected representation.
    617616      </p>
    618617      <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a id="intro.requirements" href="#intro.requirements">Requirements</a></h2>
    … …  
    632631         and WSP (whitespace).
    633632      </p>
    634       <h3 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1</a>&nbsp;<a id="core.rules" href="#core.rules">Core Rules</a></h3>
    635       <p id="rfc.section.1.2.1.p.1">The core rules below are defined in <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>:
    636       </p>
    637       <div id="rfc.figure.u.1"></div><pre class="inline">  <a href="#core.rules" class="smpl">quoted-string</a> = &lt;quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>&gt;
    638   <a href="#core.rules" class="smpl">OWS</a>           = &lt;OWS, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>&gt;
    639 </pre><h3 id="rfc.section.1.2.2"><a href="#rfc.section.1.2.2">1.2.2</a>&nbsp;<a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3>
    640       <p id="rfc.section.1.2.2.p.1">The ABNF rules below are defined in other parts:</p>
    641       <div id="rfc.figure.u.2"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">HTTP-date</a>     = &lt;HTTP-date, defined in <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#date.time.formats.full.date" title="Date/Time Formats: Full Date">Section 6.1</a>&gt;
    642 </pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="entity.tags" href="#entity.tags">Entity-Tags</a></h1>
    643       <p id="rfc.section.2.p.1">Entity-tags are used for comparing two or more representations of the same resource. HTTP/1.1 uses entity-tags in the ETag
     633      <p id="rfc.section.1.2.p.3">The ABNF rules below are defined in other parts:</p>
     634      <div id="rfc.figure.u.1"></div><pre class="inline">  <a href="#notation" class="smpl">quoted-string</a> = &lt;quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>&gt;
     635  <a href="#notation" class="smpl">OWS</a>           = &lt;OWS, defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>&gt;
     636  <a href="#notation" class="smpl">HTTP-date</a>     = &lt;HTTP-date, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#date.time.formats.full.date" title="Date/Time Formats: Full Date">Section 6.1</a>&gt;
     637</pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="resource.metadata" href="#resource.metadata">Resource State Metadata</a></h1>
     638      <p id="rfc.section.2.p.1">This specification defines two forms of metadata that are commonly used to observe resource state and test for preconditions:
     639         modification dates and opaque entity tags. Additional metadata that reflects resource state has been defined by various extensions
     640         of HTTP, such as WebDAV <a href="#RFC4918" id="rfc.xref.RFC4918.1"><cite title="HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)">[RFC4918]</cite></a>, that are beyond the scope of this specification.
     641      </p>
     642      <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="entity.tags" href="#entity.tags">Entity Tags</a></h2>
     643      <p id="rfc.section.2.1.p.1">Entity-tags are used for comparing two or more representations of the same resource. HTTP/1.1 uses entity-tags in the ETag
    644644         (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;6.1</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section&nbsp;6.2</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section&nbsp;6.4</a>), and If-Range (<a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;4</a>. An entity-tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.
    645645      </p>
    646       <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  <a href="#entity.tags" class="smpl">entity-tag</a> = [ <a href="#entity.tags" class="smpl">weak</a> ] <a href="#entity.tags" class="smpl">opaque-tag</a>
     646      <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  <a href="#entity.tags" class="smpl">entity-tag</a> = [ <a href="#entity.tags" class="smpl">weak</a> ] <a href="#entity.tags" class="smpl">opaque-tag</a>
    647647  <a href="#entity.tags" class="smpl">weak</a>       = %x57.2F ; "W/", case-sensitive
    648   <a href="#entity.tags" class="smpl">opaque-tag</a> = <a href="#core.rules" class="smpl">quoted-string</a>
    649 </pre><p id="rfc.section.2.p.3">A "strong entity-tag" <em class="bcp14">MAY</em> be shared by two representations of a resource only if they are equivalent by octet equality.
    650       </p>
    651       <p id="rfc.section.2.p.4">A "weak entity-tag", indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two representations of a resource. A weak entity-tag can only be used for weak comparison.
    652       </p>
    653       <p id="rfc.section.2.p.5">Cache entries might persist for arbitrarily long periods, regardless of expiration times, so it is inappropriate to expect
     648  <a href="#entity.tags" class="smpl">opaque-tag</a> = <a href="#notation" class="smpl">quoted-string</a>
     649</pre><p id="rfc.section.2.1.p.3">A "strong entity-tag" <em class="bcp14">MAY</em> be shared by two representations of a resource only if they are equivalent by octet equality.
     650      </p>
     651      <p id="rfc.section.2.1.p.4">A "weak entity-tag", indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two representations of a resource. A weak entity-tag can only be used for weak comparison.
     652      </p>
     653      <p id="rfc.section.2.1.p.5">Cache entries might persist for arbitrarily long periods, regardless of expiration times, so it is inappropriate to expect
    654654         that a cache will never again attempt to validate an entry using a validator that it obtained at some point in the past. A
    655655         strong entity-tag <em class="bcp14">MUST</em> be unique across all versions of all representations associated with a particular resource over time. However, there is no
    … …  
    657657         of multiple resources at the same time and does not imply that those representations are equivalent).
    658658      </p>
    659       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="example.entity.tag.vs.conneg" href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></h2>
    660       <p id="rfc.section.2.1.p.1">Consider a resource that is subject to content negotiation (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), and where the representations returned upon a GET request vary based on the Accept-Encoding request header field (<a href="p3-payload.html#header.accept-encoding" title="Accept-Encoding">Section 6.3</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>):
    661       </p>
    662       <div id="rfc.figure.u.4"></div>
     659      <h3 id="rfc.section.2.1.1"><a href="#rfc.section.2.1.1">2.1.1</a>&nbsp;<a id="example.entity.tag.vs.conneg" href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></h3>
     660      <p id="rfc.section.2.1.1.p.1">Consider a resource that is subject to content negotiation (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), and where the representations returned upon a GET request vary based on the Accept-Encoding request header field (<a href="p3-payload.html#header.accept-encoding" title="Accept-Encoding">Section 6.3</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>):
     661      </p>
     662      <div id="rfc.figure.u.3"></div>
    663663      <p>&gt;&gt; Request:</p><pre class="text2">GET /index HTTP/1.1
    664664Host: www.example.com
    665665Accept-Encoding: gzip
    666666
    667 </pre><p id="rfc.section.2.1.p.3">In this case, the response might or might not use the gzip content coding. If it does not, the response might look like:</p>
    668       <div id="rfc.figure.u.5"></div>
     667</pre><p id="rfc.section.2.1.1.p.3">In this case, the response might or might not use the gzip content coding. If it does not, the response might look like:</p>
     668      <div id="rfc.figure.u.4"></div>
    669669      <p>&gt;&gt; Response:</p><pre class="text">HTTP/1.1 200 OK
    670670Date: Thu, 26 Mar 2010 00:05:00 GMT
    … …  
    679679Hello World!
    680680Hello World!
    681 </span></pre><p id="rfc.section.2.1.p.5">An alternative representation that does use gzip content coding would be:</p>
    682       <div id="rfc.figure.u.6"></div>
     681</span></pre><p id="rfc.section.2.1.1.p.5">An alternative representation that does use gzip content coding would be:</p>
     682      <div id="rfc.figure.u.5"></div>
    683683      <p>&gt;&gt; Response:</p><pre class="text">HTTP/1.1 200 OK
    684684Date: Thu, 26 Mar 2010 00:05:00 GMT
    … …  
    689689Content-Encoding: gzip
    690690
    691 <em>...binary data...</em></pre><div class="note" id="rfc.section.2.1.p.7">
     691<em>...binary data...</em></pre><div class="note" id="rfc.section.2.1.1.p.7">
    692692         <p> <b>Note:</b> Content codings are a property of the representation, so therefore an entity-tag of an encoded representation must be distinct
    693693            from an unencoded representation to prevent conflicts during cache updates and range requests. In contrast, transfer codings
    694             (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 6.2</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) apply only during message transfer and do not require distinct entity-tags.
     694            (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 6.2</a> of <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) apply only during message transfer and do not require distinct entity-tags.
    695695         </p>
    696696      </div>
    … …  
    705705         as if it were the payload of a 200 response. The 304 response <em class="bcp14">MUST NOT</em> contain a message-body, and thus is always terminated by the first empty line after the header fields.
    706706      </p>
    707       <p id="rfc.section.3.1.p.2">A 304 response <em class="bcp14">MUST</em> include a Date header field (<a href="p1-messaging.html#header.date" title="Date">Section 9.3</a> of <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) unless its omission is required by <a href="p1-messaging.html#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 9.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. If a 200 response to the same request would have included any of the header fields Cache-Control, Content-Location, ETag,
     707      <p id="rfc.section.3.1.p.2">A 304 response <em class="bcp14">MUST</em> include a Date header field (<a href="p1-messaging.html#header.date" title="Date">Section 9.3</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) unless its omission is required by <a href="p1-messaging.html#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 9.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. If a 200 response to the same request would have included any of the header fields Cache-Control, Content-Location, ETag,
    708708         Expires, Last-Modified, or Vary, then those same header fields <em class="bcp14">MUST</em> be sent in a 304 response.
    709709      </p>
    … …  
    810810         </table>
    811811      </div>
    812       <p id="rfc.section.4.p.9">An entity-tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity-Tags">Section&nbsp;2</a> gives the syntax for entity-tags.
     812      <p id="rfc.section.4.p.9">An entity-tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity Tags">Section&nbsp;2.1</a> gives the syntax for entity-tags.
    813813      </p>
    814814      <p id="rfc.section.4.p.10">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is
    … …  
    907907      <div id="rfc.iref.h.1"></div>
    908908      <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="header.etag" href="#header.etag">ETag</a></h2>
    909       <p id="rfc.section.6.1.p.1">The "ETag" header field provides the current value of the entity-tag (see <a href="#entity.tags" title="Entity-Tags">Section&nbsp;2</a>) for one representation of the target resource. An entity-tag is intended for use as a resource-local identifier for differentiating
     909      <p id="rfc.section.6.1.p.1">The "ETag" header field provides the current value of the entity-tag (see <a href="#entity.tags" title="Entity Tags">Section&nbsp;2.1</a>) for one representation of the target resource. An entity-tag is intended for use as a resource-local identifier for differentiating
    910910         between representations of the same resource that vary over time or via content negotiation (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;4</a>).
    911911      </p>
    912       <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.4"></span>  <a href="#header.etag" class="smpl">ETag</a> = <a href="#entity.tags" class="smpl">entity-tag</a>
    913 </pre><div id="rfc.figure.u.8"></div>
     912      <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.4"></span>  <a href="#header.etag" class="smpl">ETag</a> = <a href="#entity.tags" class="smpl">entity-tag</a>
     913</pre><div id="rfc.figure.u.7"></div>
    914914      <p>Examples:</p>  <pre class="text">  ETag: "xyzzy"
    915915  ETag: W/"xyzzy"
    … …  
    932932         An If-Match field-value of "*" places the precondition on the existence of any current representation for the target resource.
    933933      </p>
    934       <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.5"></span>  <a href="#header.if-match" class="smpl">If-Match</a> = "*" / 1#<a href="#entity.tags" class="smpl">entity-tag</a>
     934      <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.5"></span>  <a href="#header.if-match" class="smpl">If-Match</a> = "*" / 1#<a href="#entity.tags" class="smpl">entity-tag</a>
    935935</pre><p id="rfc.section.6.2.p.3">If any of the entity-tags listed in the If-Match field value match the entity-tag of the selected representation for the target
    936936         resource, or if "*" is given and any current representation exists for the target resource, then the server <em class="bcp14">MAY</em> perform the request method as if the If-Match header field was not present.
    … …  
    942942      </p>
    943943      <p id="rfc.section.6.2.p.6">Examples:</p>
    944       <div id="rfc.figure.u.10"></div><pre class="text">  If-Match: "xyzzy"
     944      <div id="rfc.figure.u.9"></div><pre class="text">  If-Match: "xyzzy"
    945945  If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
    946946  If-Match: *
    … …  
    954954         the time specified in this field, then do not perform the request method; instead, respond as detailed below.
    955955      </p>
    956       <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a>
     956      <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a>
    957957</pre><p id="rfc.section.6.3.p.3">An example of the field is:</p>
    958       <div id="rfc.figure.u.12"></div><pre class="text">  If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
     958      <div id="rfc.figure.u.11"></div><pre class="text">  If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
    959959</pre><p id="rfc.section.6.3.p.5">A GET method with an If-Modified-Since header field and no Range header field requests that the selected representation be
    960960         transferred only if it has been modified since the date given by the If-Modified-Since header field. The algorithm for determining
    … …  
    10091009         for the target resource.
    10101010      </p>
    1011       <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.7"></span>  <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "*" / 1#<a href="#entity.tags" class="smpl">entity-tag</a>
     1011      <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.7"></span>  <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "*" / 1#<a href="#entity.tags" class="smpl">entity-tag</a>
    10121012</pre><p id="rfc.section.6.4.p.4">If any of the entity-tags listed in the If-None-Match field-value match the entity-tag of the selected representation, or
    10131013         if "*" is given and any current representation exists for that resource, then the server <em class="bcp14">MUST NOT</em> perform the requested method. Instead, if the request method was GET or HEAD, the server <em class="bcp14">SHOULD</em> respond with a 304 (Not Modified) status code, including the cache-related header fields (particularly ETag) of the selected
    … …  
    10201020      </p>
    10211021      <p id="rfc.section.6.4.p.7">Examples:</p>
    1022       <div id="rfc.figure.u.14"></div><pre class="text">  If-None-Match: "xyzzy"
     1022      <div id="rfc.figure.u.13"></div><pre class="text">  If-None-Match: "xyzzy"
    10231023  If-None-Match: W/"xyzzy"
    10241024  If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
    … …  
    10351035         the time specified in this field, the server <em class="bcp14">SHOULD</em> perform the request method as if the If-Unmodified-Since header field were not present.
    10361036      </p>
    1037       <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.8"></span>  <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a>
     1037      <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.8"></span>  <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a>
    10381038</pre><p id="rfc.section.6.5.p.3">An example of the field is:</p>
    1039       <div id="rfc.figure.u.16"></div><pre class="text">  If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
     1039      <div id="rfc.figure.u.15"></div><pre class="text">  If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
    10401040</pre><p id="rfc.section.6.5.p.5">If the request normally (i.e., without the If-Unmodified-Since header field) would result in anything other than a 2xx or
    10411041         412 status code, the If-Unmodified-Since header field <em class="bcp14">SHOULD</em> be ignored.
    … …  
    10521052         modified.
    10531053      </p>
    1054       <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  <a href="#header.last-modified" class="smpl">Last-Modified</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a>
     1054      <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  <a href="#header.last-modified" class="smpl">Last-Modified</a> = <a href="#notation" class="smpl">HTTP-date</a>
    10551055</pre><p id="rfc.section.6.6.p.3">An example of its use is</p>
    1056       <div id="rfc.figure.u.18"></div><pre class="text">  Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
     1056      <div id="rfc.figure.u.17"></div><pre class="text">  Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
    10571057</pre><p id="rfc.section.6.6.p.5">A representation is typically the sum of many parts behind the resource interface. The last-modified time would usually be
    10581058         the most recent time that any of those parts were changed. How that value is determined for any given resource is an implementation
    … …  
    11641164      <p id="rfc.section.7.2.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
    11651165      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
    1166       <p id="rfc.section.8.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.9"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
     1166      <p id="rfc.section.8.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
    11671167      </p>
    11681168      <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
    … …  
    12051205      <h2 id="rfc.references.2"><a href="#rfc.section.10.2" id="rfc.section.10.2">10.2</a> Informative References
    12061206      </h2>
    1207       <table>   
     1207      <table>     
    12081208         <tr>
    12091209            <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
    … …  
    12141214            <td class="reference"><b id="RFC3864">[RFC3864]</b></td>
    12151215            <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="http://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP&nbsp;90, RFC&nbsp;3864, September&nbsp;2004.
     1216            </td>
     1217         </tr>
     1218         <tr>
     1219            <td class="reference"><b id="RFC4918">[RFC4918]</b></td>
     1220            <td class="top"><a href="mailto:ldusseault@commerce.net" title="CommerceNet">Dusseault, L., Ed.</a>, “<a href="http://tools.ietf.org/html/rfc4918">HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)</a>”, RFC&nbsp;4918, June&nbsp;2007.
    12161221            </td>
    12171222         </tr>
    … …  
    12411246      </p>
    12421247      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1>
    1243       <div id="rfc.figure.u.19"></div> <pre class="inline"><a href="#header.etag" class="smpl">ETag</a> = entity-tag
    1244 
    1245 <a href="#abnf.dependencies" class="smpl">HTTP-date</a> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
     1248      <div id="rfc.figure.u.18"></div> <pre class="inline"><a href="#header.etag" class="smpl">ETag</a> = entity-tag
     1249
     1250<a href="#notation" class="smpl">HTTP-date</a> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
    12461251
    12471252<a href="#header.if-match" class="smpl">If-Match</a> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
    … …  
    12541259<a href="#header.last-modified" class="smpl">Last-Modified</a> = HTTP-date
    12551260
    1256 <a href="#core.rules" class="smpl">OWS</a> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
     1261<a href="#notation" class="smpl">OWS</a> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
    12571262
    12581263<a href="#entity.tags" class="smpl">entity-tag</a> = [ weak ] opaque-tag
    … …  
    12601265<a href="#entity.tags" class="smpl">opaque-tag</a> = quoted-string
    12611266
    1262 <a href="#core.rules" class="smpl">quoted-string</a> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
     1267<a href="#notation" class="smpl">quoted-string</a> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
    12631268
    12641269<a href="#entity.tags" class="smpl">weak</a> = %x57.2F ; W/
    1265 </pre> <div id="rfc.figure.u.20"></div>
     1270</pre> <div id="rfc.figure.u.19"></div>
    12661271      <p>ABNF diagnostics:</p><pre class="inline">; ETag defined but not used
    12671272; If-Match defined but not used
    … …  
    12731278      <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a>&nbsp;Since RFC 2616
    12741279      </h2>
    1275       <p id="rfc.section.C.1.p.1">Extracted relevant partitions from <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
     1280      <p id="rfc.section.C.1.p.1">Extracted relevant partitions from <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
    12761281      </p>
    12771282      <h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a>&nbsp;Since draft-ietf-httpbis-p4-conditional-00
    … …  
    13881393            </li>
    13891394            <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul>
    1390                   <li>ETag header field&nbsp;&nbsp;<a href="#rfc.xref.header.etag.1">2</a>, <a href="#rfc.iref.e.1"><b>6.1</b></a>, <a href="#rfc.xref.header.etag.2">7.2</a></li>
     1395                  <li>ETag header field&nbsp;&nbsp;<a href="#rfc.xref.header.etag.1">2.1</a>, <a href="#rfc.iref.e.1"><b>6.1</b></a>, <a href="#rfc.xref.header.etag.2">7.2</a></li>
    13911396               </ul>
    13921397            </li>
    … …  
    13941399                  <li><tt>Grammar</tt>&nbsp;&nbsp;
    13951400                     <ul>
    1396                         <li><tt>entity-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2</b></a></li>
     1401                        <li><tt>entity-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2.1</b></a></li>
    13971402                        <li><tt>ETag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>6.1</b></a></li>
    13981403                        <li><tt>If-Match</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>6.2</b></a></li>
    … …  
    14011406                        <li><tt>If-Unmodified-Since</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>6.5</b></a></li>
    14021407                        <li><tt>Last-Modified</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>6.6</b></a></li>
    1403                         <li><tt>opaque-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>2</b></a></li>
    1404                         <li><tt>weak</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2</b></a></li>
     1408                        <li><tt>opaque-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>2.1</b></a></li>
     1409                        <li><tt>weak</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2.1</b></a></li>
    14051410                     </ul>
    14061411                  </li>
    … …  
    14101415                  <li>Header Fields&nbsp;&nbsp;
    14111416                     <ul>
    1412                         <li>ETag&nbsp;&nbsp;<a href="#rfc.xref.header.etag.1">2</a>, <a href="#rfc.iref.h.1"><b>6.1</b></a>, <a href="#rfc.xref.header.etag.2">7.2</a></li>
    1413                         <li>If-Match&nbsp;&nbsp;<a href="#rfc.xref.header.if-match.1">2</a>, <a href="#rfc.iref.h.2"><b>6.2</b></a>, <a href="#rfc.xref.header.if-match.2">7.2</a></li>
     1417                        <li>ETag&nbsp;&nbsp;<a href="#rfc.xref.header.etag.1">2.1</a>, <a href="#rfc.iref.h.1"><b>6.1</b></a>, <a href="#rfc.xref.header.etag.2">7.2</a></li>
     1418                        <li>If-Match&nbsp;&nbsp;<a href="#rfc.xref.header.if-match.1">2.1</a>, <a href="#rfc.iref.h.2"><b>6.2</b></a>, <a href="#rfc.xref.header.if-match.2">7.2</a></li>
    14141419                        <li>If-Modified-Since&nbsp;&nbsp;<a href="#rfc.iref.h.3"><b>6.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">7.2</a></li>
    1415                         <li>If-None-Match&nbsp;&nbsp;<a href="#rfc.xref.header.if-none-match.1">2</a>, <a href="#rfc.iref.h.4"><b>6.4</b></a>, <a href="#rfc.xref.header.if-none-match.2">7.2</a>, <a href="#rfc.xref.header.if-none-match.3">A</a></li>
     1420                        <li>If-None-Match&nbsp;&nbsp;<a href="#rfc.xref.header.if-none-match.1">2.1</a>, <a href="#rfc.iref.h.4"><b>6.4</b></a>, <a href="#rfc.xref.header.if-none-match.2">7.2</a>, <a href="#rfc.xref.header.if-none-match.3">A</a></li>
    14161421                        <li>If-Unmodified-Since&nbsp;&nbsp;<a href="#rfc.iref.h.5"><b>6.5</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">7.2</a></li>
    14171422                        <li>Last-Modified&nbsp;&nbsp;<a href="#rfc.iref.h.6"><b>6.6</b></a>, <a href="#rfc.xref.header.last-modified.1">7.2</a></li>
    … …  
    14211426            </li>
    14221427            <li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul>
    1423                   <li>If-Match header field&nbsp;&nbsp;<a href="#rfc.xref.header.if-match.1">2</a>, <a href="#rfc.iref.i.1"><b>6.2</b></a>, <a href="#rfc.xref.header.if-match.2">7.2</a></li>
     1428                  <li>If-Match header field&nbsp;&nbsp;<a href="#rfc.xref.header.if-match.1">2.1</a>, <a href="#rfc.iref.i.1"><b>6.2</b></a>, <a href="#rfc.xref.header.if-match.2">7.2</a></li>
    14241429                  <li>If-Modified-Since header field&nbsp;&nbsp;<a href="#rfc.iref.i.2"><b>6.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">7.2</a></li>
    1425                   <li>If-None-Match header field&nbsp;&nbsp;<a href="#rfc.xref.header.if-none-match.1">2</a>, <a href="#rfc.iref.i.3"><b>6.4</b></a>, <a href="#rfc.xref.header.if-none-match.2">7.2</a>, <a href="#rfc.xref.header.if-none-match.3">A</a></li>
     1430                  <li>If-None-Match header field&nbsp;&nbsp;<a href="#rfc.xref.header.if-none-match.1">2.1</a>, <a href="#rfc.iref.i.3"><b>6.4</b></a>, <a href="#rfc.xref.header.if-none-match.2">7.2</a>, <a href="#rfc.xref.header.if-none-match.3">A</a></li>
    14261431                  <li>If-Unmodified-Since header field&nbsp;&nbsp;<a href="#rfc.iref.i.4"><b>6.5</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">7.2</a></li>
    14271432               </ul>
    … …  
    14321437            </li>
    14331438            <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
    1434                   <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.2</a>, <a href="#rfc.xref.Part1.2">1.2.1</a>, <a href="#rfc.xref.Part1.3">1.2.1</a>, <a href="#rfc.xref.Part1.4">1.2.1</a>, <a href="#rfc.xref.Part1.5">1.2.2</a>, <a href="#rfc.xref.Part1.6">2.1</a>, <a href="#rfc.xref.Part1.7">3.1</a>, <a href="#rfc.xref.Part1.8">3.1</a>, <a href="#rfc.xref.Part1.9">8</a>, <a href="#Part1"><b>10.1</b></a><ul>
     1439                  <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.2</a>, <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">1.2</a>, <a href="#rfc.xref.Part1.5">2.1.1</a>, <a href="#rfc.xref.Part1.6">3.1</a>, <a href="#rfc.xref.Part1.7">3.1</a>, <a href="#rfc.xref.Part1.8">8</a>, <a href="#Part1"><b>10.1</b></a><ul>
    14351440                        <li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.2</a></li>
    1436                         <li><em>Section 1.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">1.2.1</a>, <a href="#rfc.xref.Part1.3">1.2.1</a>, <a href="#rfc.xref.Part1.4">1.2.1</a></li>
    1437                         <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">1.2.2</a></li>
    1438                         <li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.6">2.1</a></li>
    1439                         <li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">3.1</a></li>
    1440                         <li><em>Section 9.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.8">3.1</a></li>
     1441                        <li><em>Section 1.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2</a></li>
     1442                        <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.4">1.2</a></li>
     1443                        <li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">2.1.1</a></li>
     1444                        <li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.6">3.1</a></li>
     1445                        <li><em>Section 9.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">3.1</a></li>
    14411446                     </ul>
    14421447                  </li>
    1443                   <li><em>Part3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.1</a>, <a href="#rfc.xref.Part3.2">2.1</a>, <a href="#Part3"><b>10.1</b></a><ul>
    1444                         <li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.1</a></li>
    1445                         <li><em>Section 6.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.2">2.1</a></li>
     1448                  <li><em>Part3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.1.1</a>, <a href="#rfc.xref.Part3.2">2.1.1</a>, <a href="#Part3"><b>10.1</b></a><ul>
     1449                        <li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.1.1</a></li>
     1450                        <li><em>Section 6.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.2">2.1.1</a></li>
    14461451                     </ul>
    14471452                  </li>
    1448                   <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2</a>, <a href="#rfc.xref.Part5.2">4</a>, <a href="#rfc.xref.Part5.3">4</a>, <a href="#rfc.xref.Part5.4">6.3</a>, <a href="#Part5"><b>10.1</b></a><ul>
    1449                         <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2</a></li>
     1453                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.1</a>, <a href="#rfc.xref.Part5.2">4</a>, <a href="#rfc.xref.Part5.3">4</a>, <a href="#rfc.xref.Part5.4">6.3</a>, <a href="#Part5"><b>10.1</b></a><ul>
     1454                        <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.1</a></li>
    14501455                        <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.4">6.3</a></li>
    14511456                     </ul>
    14521457                  </li>
    1453                   <li><em>Part6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">1</a>, <a href="#Part6"><b>10.1</b></a></li>
     1458                  <li><em>Part6</em>&nbsp;&nbsp;<a href="#Part6"><b>10.1</b></a></li>
    14541459               </ul>
    14551460            </li>
    14561461            <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul>
    14571462                  <li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>10.1</b></a></li>
    1458                   <li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">1</a>, <a href="#RFC2616"><b>10.2</b></a>, <a href="#rfc.xref.RFC2616.2">C.1</a></li>
     1463                  <li><em>RFC2616</em>&nbsp;&nbsp;<a href="#RFC2616"><b>10.2</b></a>, <a href="#rfc.xref.RFC2616.1">C.1</a></li>
    14591464                  <li><em>RFC3864</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3864.1">7.2</a>, <a href="#RFC3864"><b>10.2</b></a></li>
     1465                  <li><em>RFC4918</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4918.1">2</a>, <a href="#RFC4918"><b>10.2</b></a></li>
    14601466                  <li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">1.2</a>, <a href="#RFC5234"><b>10.1</b></a><ul>
    14611467                        <li><em>Appendix B.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.2">1.2</a></li>

  • draft-ietf-httpbis/latest/p4-conditional.xml

    r1243 r1251  
    216216<section title="Introduction" anchor="introduction">
    217217<t>
    218    This document defines HTTP/1.1 response metadata for indicating potential
    219    changes to payload content, including modification time stamps and opaque
    220    entity-tags, and the HTTP conditional request mechanisms that allow
    221    preconditions to be placed on a request method.  Conditional GET requests
    222    allow for efficient cache updates.  Other conditional request methods are
    223    used to protect against overwriting or misunderstanding the state of a
    224    resource that has been changed unbeknownst to the requesting client.
     218   This document defines the HTTP/1.1 conditional request mechanisms,
     219   including both response metadata that can be used to indicate or
     220   observe changes to resource state and request header fields that
     221   specify preconditions to be checked before performing the action
     222   given by the request method.  Conditional GET requests are the most
     223   efficient mechanism for HTTP cache updates.  Conditionals can be
     224   applied to state-changing methods, such as PUT and DELETE, to prevent
     225   the "lost update" problem: one client accidentally overwriting
     226   the work of another client that has been acting in parallel.
     227</t>
     228<t>
     229   Conditional request preconditions are based on the state of the target
     230   resource as a whole (its current value set) or the state as observed
     231   in a previously obtained representation (one value in that set).
     232   A resource might have multiple current representations, each with its
     233   own observable state.  The conditional request mechanisms assume that
     234   the mapping of requests to corresponding representations will be
     235   consistent over time if the server intends to take advantage of
     236   conditionals.  Regardless, if the mapping is inconsistent and
     237   the server is unable to select the appropriate representation, then
     238   no harm will result when the precondition evaluates to false.
    225239</t>
    226240<t><iref primary="true" item="selected representation"/>
    227    We use the term "<x:dfn>selected representation</x:dfn>" to refer to the current
    228    representation of the target resource that would have been selected
    229    and sent as payload in a 200 (OK) response if the same request had used
    230    the method GET and had excluded all of the conditional request header
    231    fields.  The conditions found within conditional requests are evaluated
    232    on the basis of either the state of the target resource as a whole or
    233    the state of the target resource's selected representation.
    234 </t>
    235 <t>
    236    This document is currently disorganized in order to minimize the changes
    237    between drafts and enable reviewers to see the smaller errata changes.
    238    A future draft will reorganize the sections to better reflect the content.
    239    In particular, the sections on resource metadata will be discussed first
    240    and then followed by each conditional request header field, concluding with a
    241    definition of precedence and the expectation of ordering strong validator
    242    checks before weak validator checks.  It is likely that more content from
    243    &caching; will migrate to this part, where appropriate.
    244    The current mess reflects how widely dispersed these topics and associated
    245    requirements had become in <xref target="RFC2616"/>.
     241   We use the term "<x:dfn>selected representation</x:dfn>" to refer to
     242   the current representation of the target resource that would have been
     243   selected in a successful response if the same request had used the method
     244   GET and had excluded all of the conditional request header fields.
     245   The conditional request preconditions are evaluated by comparing the
     246   values provided in the request header fields to the current metadata
     247   for the selected representation.
    246248</t>
    247249
    … …  
    271273  <x:anchor-alias value="VCHAR"/>
    272274  <x:anchor-alias value="WSP"/>
     275  <x:anchor-alias value="core.rules"/>
     276  <x:anchor-alias value="quoted-string"/>
     277  <x:anchor-alias value="OWS"/>
     278  <x:anchor-alias value="HTTP-date"/>
    273279<t>
    274280  This specification uses the ABNF syntax defined in &notation; (which
    … …  
    287293  and WSP (whitespace).
    288294</t>
    289 
    290 <section title="Core Rules" anchor="core.rules">
    291   <x:anchor-alias value="quoted-string"/>
    292   <x:anchor-alias value="OWS"/>
    293 <t>
    294   The core rules below are defined in &basic-rules;:
     295<t>
     296  The ABNF rules below are defined in other parts:
    295297</t>
    296298<figure><artwork type="abnf2616">
    297299  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
    298300  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
    299 </artwork></figure>
    300 </section>
    301 
    302 <section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
    303   <x:anchor-alias value="HTTP-date"/>
    304 <t>
    305   The ABNF rules below are defined in other parts:
    306 </t>
    307 <figure><!--Part1--><artwork type="abnf2616">
    308301  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
    309302</artwork></figure>
    310303</section>
    311 
    312 </section>
    313 
    314 </section>
    315 
    316 <section title="Entity-Tags" anchor="entity.tags">
     304</section>
     305
     306<section title="Resource State Metadata" anchor="resource.metadata">
     307<t>
     308   This specification defines two forms of metadata that are commonly used
     309   to observe resource state and test for preconditions: modification dates
     310   and opaque entity tags.  Additional metadata that reflects resource state
     311   has been defined by various extensions of HTTP, such as WebDAV
     312   <xref target="RFC4918"/>, that are beyond the scope of this specification.
     313</t>
     314
     315<section title="Entity Tags" anchor="entity.tags">
    317316  <x:anchor-alias value="entity-tag"/>
    318317  <x:anchor-alias value="opaque-tag"/>
    … …  
    406405  </t>
    407406</x:note>
     407</section>
    408408</section>
    409409</section>
    … …  
    14451445</reference>
    14461446
     1447<reference anchor='RFC4918'>
     1448  <front>
     1449    <title>HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)</title>
     1450    <author initials="L.M." surname="Dusseault" fullname="Lisa Dusseault" role="editor" >
     1451      <organization abbrev="CommerceNet">CommerceNet</organization>
     1452      <address><email>ldusseault@commerce.net</email></address>
     1453    </author>
     1454    <date month="June" year="2007" />
     1455  </front>
     1456  <seriesInfo name='RFC' value='4918' />
     1457</reference>
    14471458</references>
    14481459
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