Changeset 1260 for draft-ietf-httpbis/latest

Timestamp:

05/04/11 22:49:27 (11 years ago)

Author:

fielding@…

Message:

editorial: rearrange p4 a bit more to split discussion of last-modified
from that of entity-tags, move entity-tags definition within the ETag
header field, and introduce sections for requirements on generation
and comparison of each (separately). This roughly halves the
cognitive complexity of the existing descriptions and allows us
to get rid of a lot of duplication (with more to come).

Moved some stray requirements on range requests to p5.

Location:

draft-ietf-httpbis/latest

Files:

• p1-messaging.html (modified) (5 diffs)
• p2-semantics.html (modified) (8 diffs)
• p3-payload.html (modified) (5 diffs)
• p4-conditional.html (modified) (35 diffs)
• p4-conditional.xml (modified) (13 diffs)
• p5-range.html (modified) (10 diffs)
• p5-range.xml (modified) (5 diffs)
• p6-cache.html (modified) (7 diffs)
• p7-auth.html (modified) (5 diffs)

draft-ietf-httpbis/latest/p1-messaging.html

@@ -359 +359 @@
   } 
   @bottom-center {
-       content: "Expires October 6, 2011"; 
+       content: "Expires October 7, 2011"; 
   } 
   @bottom-right {
@@ -410 +410 @@
       <meta name="dct.creator" content="Reschke, J. F.">
       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p1-messaging-latest">
-      <meta name="dct.issued" scheme="ISO8601" content="2011-04-04">
+      <meta name="dct.issued" scheme="ISO8601" content="2011-04-05">
       <meta name="dct.replaces" content="urn:ietf:rfc:2145">
       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
@@ -442 +442 @@
             </tr>
             <tr>
-               <td class="left">Expires: October 6, 2011</td>
+               <td class="left">Expires: October 7, 2011</td>
                <td class="right">HP</td>
             </tr>
@@ -495 +495 @@
             <tr>
                <td class="left"></td>
-               <td class="right">April 4, 2011</td>
+               <td class="right">April 5, 2011</td>
             </tr>
          </tbody>
@@ -523 +523 @@
          in progress”.
       </p>
-      <p>This Internet-Draft will expire on October 6, 2011.</p>
+      <p>This Internet-Draft will expire on October 7, 2011.</p>
       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
       <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>

draft-ietf-httpbis/latest/p2-semantics.html

@@ -359 +359 @@
   } 
   @bottom-center {
-       content: "Expires October 6, 2011"; 
+       content: "Expires October 7, 2011"; 
   } 
   @bottom-right {
@@ -409 +409 @@
       <meta name="dct.creator" content="Reschke, J. F.">
       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p2-semantics-latest">
-      <meta name="dct.issued" scheme="ISO8601" content="2011-04-04">
+      <meta name="dct.issued" scheme="ISO8601" content="2011-04-05">
       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
       <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 2 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 2 defines the semantics of HTTP messages as expressed by request methods, request header fields, response status codes, and response header fields.">
@@ -440 +440 @@
             </tr>
             <tr>
-               <td class="left">Expires: October 6, 2011</td>
+               <td class="left">Expires: October 7, 2011</td>
                <td class="right">HP</td>
             </tr>
@@ -493 +493 @@
             <tr>
                <td class="left"></td>
-               <td class="right">April 4, 2011</td>
+               <td class="right">April 5, 2011</td>
             </tr>
          </tbody>
@@ -520 +520 @@
          in progress”.
       </p>
-      <p>This Internet-Draft will expire on October 6, 2011.</p>
+      <p>This Internet-Draft will expire on October 7, 2011.</p>
       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
       <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
@@ -1212 +1212 @@
                <tr>
                   <td class="left">ETag</td>
-                  <td class="left"><a href="p4-conditional.html#header.etag" title="ETag">Section 2.2.1</a> of <a href="#Part4" id="rfc.xref.Part4.8"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
+                  <td class="left"><a href="p4-conditional.html#header.etag" title="ETag">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.8"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a></td>
                </tr>
                <tr>
@@ -1569 +1569 @@
       </p>
       <p id="rfc.section.8.2.2.p.2">A 201 response <em class="bcp14">MAY</em> contain an ETag response header field indicating the current value of the entity-tag for the representation of the resource
-         just created (see <a href="p4-conditional.html#header.etag" title="ETag">Section 2.2.1</a> of <a href="#Part4" id="rfc.xref.Part4.9"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
+         just created (see <a href="p4-conditional.html#header.etag" title="ETag">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.9"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
       </p>
       <div id="rfc.iref.26"></div>
@@ -3206 +3206 @@
                   </li>
                   <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">3</a>, <a href="#rfc.xref.Part4.2">3</a>, <a href="#rfc.xref.Part4.3">3</a>, <a href="#rfc.xref.Part4.4">3</a>, <a href="#rfc.xref.Part4.5">4.1</a>, <a href="#rfc.xref.Part4.6">4.1</a>, <a href="#rfc.xref.Part4.7">4.1</a>, <a href="#rfc.xref.Part4.8">5</a>, <a href="#rfc.xref.Part4.9">8.2.2</a>, <a href="#rfc.xref.Part4.10">8.3.5</a>, <a href="#rfc.xref.Part4.11">8.4.13</a>, <a href="#Part4"><b>13.1</b></a>, <a href="#rfc.xref.Part4.12">C.2</a><ul>
-                        <li><em>Section 2.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.8">5</a>, <a href="#rfc.xref.Part4.9">8.2.2</a></li>
+                        <li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.8">5</a>, <a href="#rfc.xref.Part4.9">8.2.2</a></li>
                         <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">3</a></li>
                         <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">3</a></li>

draft-ietf-httpbis/latest/p3-payload.html

@@ -359 +359 @@
   } 
   @bottom-center {
-       content: "Expires October 6, 2011"; 
+       content: "Expires October 7, 2011"; 
   } 
   @bottom-right {
@@ -408 +408 @@
       <meta name="dct.creator" content="Reschke, J. F.">
       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p3-payload-latest">
-      <meta name="dct.issued" scheme="ISO8601" content="2011-04-04">
+      <meta name="dct.issued" scheme="ISO8601" content="2011-04-05">
       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
       <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 3 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 3 defines HTTP message content, metadata, and content negotiation.">
@@ -434 +434 @@
             </tr>
             <tr>
-               <td class="left">Expires: October 6, 2011</td>
+               <td class="left">Expires: October 7, 2011</td>
                <td class="right">J. Mogul</td>
             </tr>
@@ -491 +491 @@
             <tr>
                <td class="left"></td>
-               <td class="right">April 4, 2011</td>
+               <td class="right">April 5, 2011</td>
             </tr>
          </tbody>
@@ -517 +517 @@
          in progress”.
       </p>
-      <p>This Internet-Draft will expire on October 6, 2011.</p>
+      <p>This Internet-Draft will expire on October 7, 2011.</p>
       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
       <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>

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

@@ -359 +359 @@
   } 
   @bottom-center {
-       content: "Expires October 6, 2011"; 
+       content: "Expires October 7, 2011"; 
   } 
   @bottom-right {
@@ -404 +404 @@
       <meta name="dct.creator" content="Reschke, J. F.">
       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p4-conditional-latest">
-      <meta name="dct.issued" scheme="ISO8601" content="2011-04-04">
+      <meta name="dct.issued" scheme="ISO8601" content="2011-04-05">
       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
       <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.">
@@ -430 +430 @@
             </tr>
             <tr>
-               <td class="left">Expires: October 6, 2011</td>
+               <td class="left">Expires: October 7, 2011</td>
                <td class="right">J. Mogul</td>
             </tr>
@@ -487 +487 @@
             <tr>
                <td class="left"></td>
-               <td class="right">April 4, 2011</td>
+               <td class="right">April 5, 2011</td>
             </tr>
          </tbody>
@@ -513 +513 @@
          in progress”.
       </p>
-      <p>This Internet-Draft will expire on October 6, 2011.</p>
+      <p>This Internet-Draft will expire on October 7, 2011.</p>
       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
       <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
@@ -537 +537 @@
          </li>
          <li>2.&nbsp;&nbsp;&nbsp;<a href="#resource.metadata">Resource State Metadata (Validators)</a><ul>
-               <li>2.1&nbsp;&nbsp;&nbsp;<a href="#header.last-modified">Last-Modified</a></li>
-               <li>2.2&nbsp;&nbsp;&nbsp;<a href="#entity.tags">Entity Tags</a><ul>
-                     <li>2.2.1&nbsp;&nbsp;&nbsp;<a href="#header.etag">ETag</a></li>
-                     <li>2.2.2&nbsp;&nbsp;&nbsp;<a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li>
+               <li>2.1&nbsp;&nbsp;&nbsp;<a href="#header.last-modified">Last-Modified</a><ul>
+                     <li>2.1.1&nbsp;&nbsp;&nbsp;<a href="#lastmod.generation">Generation</a></li>
+                     <li>2.1.2&nbsp;&nbsp;&nbsp;<a href="#lastmod.comparison">Comparison</a></li>
                   </ul>
                </li>
-               <li>2.3&nbsp;&nbsp;&nbsp;<a href="#weak.and.strong.validators">Weak and Strong Validators</a></li>
-               <li>2.4&nbsp;&nbsp;&nbsp;<a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity-tags and Last-Modified Dates</a></li>
+               <li>2.2&nbsp;&nbsp;&nbsp;<a href="#header.etag">ETag</a><ul>
+                     <li>2.2.1&nbsp;&nbsp;&nbsp;<a href="#entity.tag.generation">Generation</a></li>
+                     <li>2.2.2&nbsp;&nbsp;&nbsp;<a href="#weak.and.strong.validators">Weak versus Strong</a></li>
+                     <li>2.2.3&nbsp;&nbsp;&nbsp;<a href="#entity.tag.comparison">Comparison</a></li>
+                     <li>2.2.4&nbsp;&nbsp;&nbsp;<a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity-tags and Last-Modified Dates</a></li>
+                     <li>2.2.5&nbsp;&nbsp;&nbsp;<a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li>
+                  </ul>
+               </li>
             </ul>
          </li>
@@ -552 +557 @@
                <li>3.3&nbsp;&nbsp;&nbsp;<a href="#header.if-modified-since">If-Modified-Since</a></li>
                <li>3.4&nbsp;&nbsp;&nbsp;<a href="#header.if-unmodified-since">If-Unmodified-Since</a></li>
+               <li>3.5&nbsp;&nbsp;&nbsp;<a href="#header.if-range">If-Range</a></li>
             </ul>
          </li>
@@ -597 +603 @@
       <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
          or observe changes to resource state and request header fields that specify preconditions to be checked before performing
-         the action given by the request method. Conditional GET requests are the most efficient mechanism for HTTP cache updates <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Conditionals can be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem: one
-         client accidentally overwriting the work of another client that has been acting in parallel.
+         the action given by the request method. Conditional GET requests are the most efficient mechanism for HTTP cache updates <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Conditionals can also be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem:
+         one client accidentally overwriting the work of another client that has been acting in parallel.
       </p>
       <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
@@ -637 +643 @@
       <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:
          modification dates and opaque entity tags. Additional metadata that reflects resource state has been defined by various extensions
-         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. Such metadata is referred to as a "<dfn>validator</dfn>" when it is used within a precondition.
+         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. A resource metadata value is referred to as a "<dfn>validator</dfn>" when it is used within a precondition.
       </p>
       <div id="rfc.iref.l.1"></div>
       <div id="rfc.iref.h.1"></div>
       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2>
-      <p id="rfc.section.2.1.p.1">The "Last-Modified" header field indicates the date and time at which the origin server believes the representation was last
-         modified.
+      <p id="rfc.section.2.1.p.1">The "Last-Modified" header field indicates the date and time at which the origin server believes the selected representation
+         was last modified.
       </p>
       <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.1"></span>  <a href="#header.last-modified" class="smpl">Last-Modified</a> = <a href="#notation" class="smpl">HTTP-date</a>
 </pre><p id="rfc.section.2.1.p.3">An example of its use is</p>
       <div id="rfc.figure.u.3"></div><pre class="text">  Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
-</pre><p id="rfc.section.2.1.p.5">A representation is typically the sum of many parts behind the resource interface. The last-modified time would usually be
+</pre><h3 id="rfc.section.2.1.1"><a href="#rfc.section.2.1.1">2.1.1</a>&nbsp;<a id="lastmod.generation" href="#lastmod.generation">Generation</a></h3>
+      <p id="rfc.section.2.1.1.p.1">Origin servers <em class="bcp14">SHOULD</em> send Last-Modified for any selected representation for which a last modification date can be reasonably and consistently determined,
+         since its use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) results in a substantial reduction of HTTP traffic on the Internet and can be a significant factor in improving service
+         scalability and reliability.
+      </p>
+      <p id="rfc.section.2.1.1.p.2">A representation is typically the sum of many parts behind the resource interface. The last-modified time would usually be
          the most recent time that any of those parts were changed. How that value is determined for any given resource is an implementation
          detail beyond the scope of this specification. What matters to HTTP is how recipients of the Last-Modified header field can
          use its value to make conditional requests and test the validity of locally cached responses.
       </p>
-      <p id="rfc.section.2.1.p.6">An origin server <em class="bcp14">MUST NOT</em> send a Last-Modified date which is later than the server's time of message origination. In such cases, where the resource's
-         last modification would indicate some time in the future, the server <em class="bcp14">MUST</em> replace that date with the message origination date.
-      </p>
-      <p id="rfc.section.2.1.p.7">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the representation as close as possible to the time that it generates the Date value of
-         its response. This allows a recipient to make an accurate assessment of the representation's modification time, especially
+      <p id="rfc.section.2.1.1.p.3">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the representation as close as possible to the time that it generates the Date field-value
+         for its response. This allows a recipient to make an accurate assessment of the representation's modification time, especially
          if the representation changes near the time that the response is generated.
       </p>
-      <p id="rfc.section.2.1.p.8">HTTP/1.1 servers <em class="bcp14">SHOULD</em> send Last-Modified whenever feasible.
-      </p>
-      <p id="rfc.section.2.1.p.9">The Last-Modified header field value is often used as a cache validator. In simple terms, a cache entry is considered to be
-         valid if the representation has not been modified since the Last-Modified value.
-      </p>
-      <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="entity.tags" href="#entity.tags">Entity Tags</a></h2>
-      <p id="rfc.section.2.2.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
-         (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;2.2.1</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section&nbsp;3.1</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section&nbsp;3.2</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;2.3</a>. An entity-tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.
-      </p>
-      <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></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>
-  <a href="#entity.tags" class="smpl">weak</a>       = %x57.2F ; "W/", case-sensitive
-  <a href="#entity.tags" class="smpl">opaque-tag</a> = <a href="#notation" class="smpl">quoted-string</a>
-</pre><p id="rfc.section.2.2.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.
-      </p>
-      <p id="rfc.section.2.2.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.
-      </p>
-      <p id="rfc.section.2.2.p.5">Cache entries might persist for arbitrarily long periods, regardless of expiration times, so it is inappropriate to expect
-         that a cache will never again attempt to validate an entry using a validator that it obtained at some point in the past. A
-         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
-         implication of uniqueness across entity-tags of different resources (i.e., the same entity-tag value might be in use for representations
-         of multiple resources at the same time and does not imply that those representations are equivalent).
+      <p id="rfc.section.2.1.1.p.4">An origin server with a clock <em class="bcp14">MUST NOT</em> send a Last-Modified date that is later than the server's time of message origination (Date). If the last modification time
+         is derived from implementation-specific metadata that evaluates to some time in the future, according to the origin server's
+         clock, then the origin server <em class="bcp14">MUST</em> replace that value with the message origination date. This prevents a future modification date from having an adverse impact
+         on cache validation.
+      </p>
+      <h3 id="rfc.section.2.1.2"><a href="#rfc.section.2.1.2">2.1.2</a>&nbsp;<a id="lastmod.comparison" href="#lastmod.comparison">Comparison</a></h3>
+      <p id="rfc.section.2.1.2.p.1">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is
+         strong, using the following rules: 
+      </p>
+      <ul>
+         <li>The validator is being compared by an origin server to the actual current validator for the representation and,</li>
+         <li>That origin server reliably knows that the associated representation did not change twice during the second covered by the
+            presented validator.
+         </li>
+      </ul>
+      <p id="rfc.section.2.1.2.p.2">or </p>
+      <ul>
+         <li>The validator is about to be used by a client in an If-Modified-Since or If-Unmodified-Since header field, because the client
+            has a cache entry for the associated representation, and
+         </li>
+         <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li>
+         <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li>
+      </ul>
+      <p id="rfc.section.2.1.2.p.3">or </p>
+      <ul>
+         <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the representation,
+            and
+         </li>
+         <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li>
+         <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li>
+      </ul>
+      <p id="rfc.section.2.1.2.p.4">This method relies on the fact that if two different responses were sent by the origin server during the same second, but
+         both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified
+         time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from
+         different clocks, or at somewhat different times during the preparation of the response. An implementation <em class="bcp14">MAY</em> use a value larger than 60 seconds, if it is believed that 60 seconds is too short.
       </p>
       <div id="rfc.iref.e.1"></div>
       <div id="rfc.iref.h.2"></div>
-      <h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a>&nbsp;<a id="header.etag" href="#header.etag">ETag</a></h3>
-      <p id="rfc.section.2.2.1.p.1">The "ETag" header field provides the current value of the entity-tag (see <a href="#entity.tags" title="Entity Tags">Section&nbsp;2.2</a>) for one representation of the target resource. An entity-tag is intended for use as a resource-local identifier for differentiating
-         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;2.3</a>).
-      </p>
-      <div id="rfc.figure.u.5"></div><pre class="inline"><span id="rfc.iref.g.5"></span>  <a href="#header.etag" class="smpl">ETag</a> = <a href="#entity.tags" class="smpl">entity-tag</a>
-</pre><div id="rfc.figure.u.6"></div>
+      <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="header.etag" href="#header.etag">ETag</a></h2>
+      <p id="rfc.section.2.2.p.1">The ETag header field provides the current entity-tag for the selected representation. An entity-tag is an opaque validator
+         for differentiating between multiple representations of the same resource, regardless of whether those multiple representations
+         are due to resource state changes over time, content negotiation resulting in multiple representations being valid at the
+         same time, or both. An entity-tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.
+      </p>
+      <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span>  <a href="#header.etag" class="smpl">ETag</a>       = <a href="#header.etag" class="smpl">entity-tag</a>
+
+  <a href="#header.etag" class="smpl">entity-tag</a> = [ <a href="#header.etag" class="smpl">weak</a> ] <a href="#header.etag" class="smpl">opaque-tag</a>
+  <a href="#header.etag" class="smpl">weak</a>       = %x57.2F ; "W/", case-sensitive
+  <a href="#header.etag" class="smpl">opaque-tag</a> = <a href="#notation" class="smpl">quoted-string</a>
+</pre><p id="rfc.section.2.2.p.3">An entity-tag can be more reliable for validation than a modification date in situations where it is inconvenient to store
+         modification dates, where the one-second resolution of HTTP date values is not sufficient, or where modification dates are
+         not consistently maintained.
+      </p>
+      <div id="rfc.figure.u.5"></div>
       <p>Examples:</p>  <pre class="text">  ETag: "xyzzy"
   ETag: W/"xyzzy"
   ETag: ""
-</pre><p id="rfc.section.2.2.1.p.4">An entity-tag provides an "opaque" cache validator that allows for more reliable validation than modification dates in situations
-         where it is inconvenient to store modification dates, where the one-second resolution of HTTP date values is not sufficient,
-         or where the origin server wishes to avoid certain paradoxes that might arise from the use of modification dates.
-      </p>
-      <p id="rfc.section.2.2.1.p.5">The principle behind entity-tags is that only the service author knows the semantics of a resource well enough to select an
-         appropriate cache validation mechanism, and the specification of any validator comparison function more complex than byte-equality
-         would open up a can of worms. Thus, comparisons of any other header fields (except Last-Modified, for compatibility with HTTP/1.0)
-         are never used for purposes of validating a cache entry.
-      </p>
-      <h3 id="rfc.section.2.2.2"><a href="#rfc.section.2.2.2">2.2.2</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>
-      <p id="rfc.section.2.2.2.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>):
-      </p>
-      <div id="rfc.figure.u.7"></div>
-      <p>&gt;&gt; Request:</p><pre class="text2">GET /index HTTP/1.1
-Host: www.example.com
-Accept-Encoding: gzip
-
-</pre><p id="rfc.section.2.2.2.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>
-      <div id="rfc.figure.u.8"></div>
-      <p>&gt;&gt; Response:</p><pre class="text">HTTP/1.1 200 OK
-Date: Thu, 26 Mar 2010 00:05:00 GMT
-ETag: "123-a"
-Content-Length: 70
-Vary: Accept-Encoding
-Content-Type: text/plain
-
-<span id="exbody">Hello World!
-Hello World!
-Hello World!
-Hello World!
-Hello World!
-</span></pre><p id="rfc.section.2.2.2.p.5">An alternative representation that does use gzip content coding would be:</p>
-      <div id="rfc.figure.u.9"></div>
-      <p>&gt;&gt; Response:</p><pre class="text">HTTP/1.1 200 OK
-Date: Thu, 26 Mar 2010 00:05:00 GMT
-ETag: "123-b"
-Content-Length: 43
-Vary: Accept-Encoding
-Content-Type: text/plain
-Content-Encoding: gzip
-
-<em>...binary data...</em></pre><div class="note" id="rfc.section.2.2.2.p.7"> 
-         <p> <b>Note:</b> Content codings are a property of the representation, so therefore an entity-tag of an encoded representation must be distinct
-            from an unencoded representation to prevent conflicts during cache updates and range requests. In contrast, transfer codings
-            (<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.
-         </p> 
-      </div>
-      <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak and Strong Validators</a></h2>
-      <p id="rfc.section.2.3.p.1">Since both origin servers and caches will compare two validators to decide if they represent the same or different representations,
+</pre><h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a>&nbsp;<a id="entity.tag.generation" href="#entity.tag.generation">Generation</a></h3>
+      <p id="rfc.section.2.2.1.p.1">The principle behind entity-tags is that only the service author knows the implementation of a resource well enough to select
+         the most accurate and efficient validation mechanism for that resource, and that any such mechanism can be mapped to a simple
+         sequence of octets for easy comparison. Since the value is opaque, there is no need for the client to be aware of how each
+         entity-tag is constructed.
+      </p>
+      <p id="rfc.section.2.2.1.p.2">For example, a resource that has implementation-specific versioning applied to all changes might use an internal revision
+         number, perhaps combined with a variance identifier for content negotiation, to accurately differentiate between representations.
+         Other implementations might use a stored hash of representation content, a combination of various filesystem attributes, or
+         a modification timestamp that has sub-second resolution.
+      </p>
+      <p id="rfc.section.2.2.1.p.3">Origin servers <em class="bcp14">SHOULD</em> send ETag for any selected representation for which detection of changes can be reasonably and consistently determined, since
+         the entity-tag's use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can result in a substantial reduction of HTTP network traffic and can be a significant factor in improving service scalability
+         and reliability.
+      </p>
+      <h3 id="rfc.section.2.2.2"><a href="#rfc.section.2.2.2">2.2.2</a>&nbsp;<a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak versus Strong</a></h3>
+      <p id="rfc.section.2.2.2.p.1">Since both origin servers and caches will compare two validators to decide if they indicate the same or different representations,
          one normally would expect that if the representation (including both representation header fields and representation body)
-         changes in any way, then the associated validator would change as well. If this is true, then we call this validator a "strong
+         changes in any way, then the associated validator would change as well. If this is true, then we call that validator a "strong
          validator". One example of a strong validator is an integer that is incremented in stable storage every time a representation
          is changed.
       </p>
-      <p id="rfc.section.2.3.p.2">However, there might be cases when a server prefers to change the validator only when it desires cached representations to
+      <p id="rfc.section.2.2.2.p.2">However, there might be cases when a server prefers to change the validator only when it desires cached representations to
          be invalidated. For example, the representation of a weather report that changes in content every second, based on dynamic
          measurements, might be grouped into sets of equivalent representations (from the origin server's perspective) in order to
@@ -753 +753 @@
          or weather quality). A validator that does not always change when the representation changes is a "weak validator".
       </p>
-      <p id="rfc.section.2.3.p.3">An entity-tag is normally a strong validator, but the protocol provides a mechanism to tag an entity-tag as "weak". One can
-         think of a strong validator as part of an identifier for a specific representation, whereas a weak validator is part of an
-         identifier for a set of equivalent representations (where this notion of equivalence is entirely governed by the origin server
-         and beyond the scope of this specification). 
-      </p>
+      <p id="rfc.section.2.2.2.p.3">One can think of a strong validator as part of an identifier for a specific representation, whereas a weak validator is part
+         of an identifier for a set of equivalent representations (where this notion of equivalence is entirely governed by the origin
+         server and beyond the scope of this specification).
+      </p>
+      <p id="rfc.section.2.2.2.p.4">An entity-tag is normally a strong validator, but the protocol provides a mechanism to tag an entity-tag as "weak". </p>
       <ul class="empty">
          <li>A representation's modification time, if defined with only one-second resolution, could be a weak validator, since it is possible
@@ -767 +767 @@
          </li>
       </ul>
-      <p id="rfc.section.2.3.p.4">A strong entity-tag <em class="bcp14">MUST</em> change whenever the associated representation changes in any way. A weak entity-tag <em class="bcp14">SHOULD</em> change whenever the origin server considers prior representations to be unacceptable as a substitute for the current representation.
+      <p id="rfc.section.2.2.2.p.5">A strong entity-tag <em class="bcp14">MUST</em> change whenever the associated representation changes in any way. A weak entity-tag <em class="bcp14">SHOULD</em> change whenever the origin server considers prior representations to be unacceptable as a substitute for the current representation.
          In other words, a weak entity tag <em class="bcp14">SHOULD</em> change whenever the origin server wants caches to invalidate old responses.
       </p>
-      <p id="rfc.section.2.3.p.5">A "use" of a validator is either when a client generates a request and includes the validator in a validating header field,
-         or when a server compares two validators.
-      </p>
-      <p id="rfc.section.2.3.p.6">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality
-         of a representation. For example, either kind is usable for a normal conditional GET. However, only a strong validator is
-         usable for range retrieval (<a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>), since otherwise the client might end up with an internally inconsistent representation. Clients <em class="bcp14">MUST NOT</em> use weak validators in range requests.
-      </p>
-      <p id="rfc.section.2.3.p.7">The only function that HTTP/1.1 defines on validators is comparison. There are two validator comparison functions, depending
-         on whether the comparison context allows the use of weak validators or not: 
+      <p id="rfc.section.2.2.2.p.6">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.
+      </p>
+      <p id="rfc.section.2.2.2.p.7">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.
+      </p>
+      <p id="rfc.section.2.2.2.p.8">Cache entries might persist for arbitrarily long periods, regardless of expiration times. Thus, a cache might attempt to validate
+         an entry using a validator that it obtained in the distant past. A 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
+         implication of uniqueness across entity-tags of different resources (i.e., the same entity-tag value might be in use for representations
+         of multiple resources at the same time and does not imply that those representations are equivalent).
+      </p>
+      <h3 id="rfc.section.2.2.3"><a href="#rfc.section.2.2.3">2.2.3</a>&nbsp;<a id="entity.tag.comparison" href="#entity.tag.comparison">Comparison</a></h3>
+      <p id="rfc.section.2.2.3.p.1">There are two entity-tag comparison functions, depending on whether the comparison context allows the use of weak validators
+         or not: 
       </p>
       <ul>
@@ -786 +789 @@
          </li>
       </ul>
-      <p id="rfc.section.2.3.p.8">The example below shows the results for a set of entity-tag pairs, and both the weak and strong comparison function results:</p>
+      <p id="rfc.section.2.2.3.p.2">A "use" of a validator is either when a client generates a request and includes the validator in a precondition, or when a
+         server compares two validators.
+      </p>
+      <p id="rfc.section.2.2.3.p.3">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality
+         of a representation. For example, either kind is usable for a normal conditional GET.
+      </p>
+      <p id="rfc.section.2.2.3.p.4">The example below shows the results for a set of entity-tag pairs, and both the weak and strong comparison function results:</p>
       <div id="rfc.table.u.1">
          <table class="tt full left" cellpadding="3" cellspacing="0">
@@ -825 +834 @@
          </table>
       </div>
-      <p id="rfc.section.2.3.p.9">An entity-tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity Tags">Section&nbsp;2.2</a> gives the syntax for entity-tags.
-      </p>
-      <p id="rfc.section.2.3.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
-         strong, using the following rules: 
-      </p>
-      <ul>
-         <li>The validator is being compared by an origin server to the actual current validator for the representation and,</li>
-         <li>That origin server reliably knows that the associated representation did not change twice during the second covered by the
-            presented validator.
-         </li>
-      </ul>
-      <p id="rfc.section.2.3.p.11">or </p>
-      <ul>
-         <li>The validator is about to be used by a client in an If-Modified-Since or If-Unmodified-Since header field, because the client
-            has a cache entry for the associated representation, and
-         </li>
-         <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li>
-         <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li>
-      </ul>
-      <p id="rfc.section.2.3.p.12">or </p>
-      <ul>
-         <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the representation,
-            and
-         </li>
-         <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li>
-         <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li>
-      </ul>
-      <p id="rfc.section.2.3.p.13">This method relies on the fact that if two different responses were sent by the origin server during the same second, but
-         both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified
-         time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from
-         different clocks, or at somewhat different times during the preparation of the response. An implementation <em class="bcp14">MAY</em> use a value larger than 60 seconds, if it is believed that 60 seconds is too short.
-      </p>
-      <p id="rfc.section.2.3.p.14">If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator,
-         it <em class="bcp14">MAY</em> do this only if the Last-Modified time is strong in the sense described here.
-      </p>
-      <p id="rfc.section.2.3.p.15">A cache or origin server receiving a conditional range request (<a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) <em class="bcp14">MUST</em> use the strong comparison function to evaluate the condition.
-      </p>
-      <p id="rfc.section.2.3.p.16">These rules allow HTTP/1.1 caches and clients to safely perform sub-range retrievals on values that have been obtained from
-         HTTP/1.0 servers.
-      </p>
-      <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity-tags and Last-Modified Dates</a></h2>
-      <p id="rfc.section.2.4.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types
+      <p id="rfc.section.2.2.3.p.5">An entity-tag is strong unless it is explicitly tagged as weak.</p>
+      <h3 id="rfc.section.2.2.4"><a href="#rfc.section.2.2.4">2.2.4</a>&nbsp;<a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity-tags and Last-Modified Dates</a></h3>
+      <p id="rfc.section.2.2.4.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types
          ought to be used, and for what purposes.
       </p>
-      <p id="rfc.section.2.4.p.2">HTTP/1.1 origin servers: </p>
+      <p id="rfc.section.2.2.4.p.2">HTTP/1.1 origin servers: </p>
       <ul>
          <li><em class="bcp14">SHOULD</em> send an entity-tag validator unless it is not feasible to generate one.
@@ -879 +849 @@
          </li>
       </ul>
-      <p id="rfc.section.2.4.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity-tag and a Last-Modified
+      <p id="rfc.section.2.2.4.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity-tag and a Last-Modified
          value.
       </p>
-      <p id="rfc.section.2.4.p.4">HTTP/1.1 clients: </p>
+      <p id="rfc.section.2.2.4.p.4">HTTP/1.1 clients: </p>
       <ul>
          <li><em class="bcp14">MUST</em> use that entity-tag in any cache-conditional request (using If-Match or If-None-Match) if an entity-tag has been provided
@@ -897 +867 @@
          </li>
       </ul>
-      <p id="rfc.section.2.4.p.5">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since
+      <p id="rfc.section.2.2.4.p.5">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since
          or If-Unmodified-Since header field) and one or more entity-tags (e.g., in an If-Match, If-None-Match, or If-Range header
          field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status code of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields
          in the request.
       </p>
-      <p id="rfc.section.2.4.p.6">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity-tags
+      <p id="rfc.section.2.2.4.p.6">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity-tags
          as cache validators, <em class="bcp14">MUST NOT</em> return a locally cached response to the client unless that cached response is consistent with all of the conditional header
          fields in the request. 
@@ -917 +887 @@
          </li>
       </ul>
+      <h3 id="rfc.section.2.2.5"><a href="#rfc.section.2.2.5">2.2.5</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>
+      <p id="rfc.section.2.2.5.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>):
+      </p>
+      <div id="rfc.figure.u.6"></div>
+      <p>&gt;&gt; Request:</p><pre class="text2">GET /index HTTP/1.1
+Host: www.example.com
+Accept-Encoding: gzip
+
+</pre><p id="rfc.section.2.2.5.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>
+      <div id="rfc.figure.u.7"></div>
+      <p>&gt;&gt; Response:</p><pre class="text">HTTP/1.1 200 OK
+Date: Thu, 26 Mar 2010 00:05:00 GMT
+ETag: "123-a"
+Content-Length: 70
+Vary: Accept-Encoding
+Content-Type: text/plain
+
+<span id="exbody">Hello World!
+Hello World!
+Hello World!
+Hello World!
+Hello World!
+</span></pre><p id="rfc.section.2.2.5.p.5">An alternative representation that does use gzip content coding would be:</p>
+      <div id="rfc.figure.u.8"></div>
+      <p>&gt;&gt; Response:</p><pre class="text">HTTP/1.1 200 OK
+Date: Thu, 26 Mar 2010 00:05:00 GMT
+ETag: "123-b"
+Content-Length: 43
+Vary: Accept-Encoding
+Content-Type: text/plain
+Content-Encoding: gzip
+
+<em>...binary data...</em></pre><div class="note" id="rfc.section.2.2.5.p.7"> 
+         <p> <b>Note:</b> Content codings are a property of the representation, so therefore an entity-tag of an encoded representation must be distinct
+            from an unencoded representation to prevent conflicts during cache updates and range requests. In contrast, transfer codings
+            (<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.
+         </p> 
+      </div>
       <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="header.fields" href="#header.fields">Precondition Header Fields</a></h1>
       <p id="rfc.section.3.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields for applying preconditions on requests.</p>
@@ -927 +935 @@
          An If-Match field-value of "*" places the precondition on the existence of any current representation for the target resource.
       </p>
-      <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  <a href="#header.if-match" class="smpl">If-Match</a> = "*" / 1#<a href="#entity.tags" class="smpl">entity-tag</a>
+      <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.6"></span>  <a href="#header.if-match" class="smpl">If-Match</a> = "*" / 1#<a href="#header.etag" class="smpl">entity-tag</a>
 </pre><p id="rfc.section.3.1.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
          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.
@@ -937 +945 @@
       </p>
       <p id="rfc.section.3.1.p.6">Examples:</p>
-      <div id="rfc.figure.u.11"></div><pre class="text">  If-Match: "xyzzy"
+      <div id="rfc.figure.u.10"></div><pre class="text">  If-Match: "xyzzy"
   If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
   If-Match: *
@@ -957 +965 @@
          for the target resource.
       </p>
-      <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>
+      <div id="rfc.figure.u.11"></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="#header.etag" class="smpl">entity-tag</a>
 </pre><p id="rfc.section.3.2.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
          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
@@ -965 +973 @@
       </p>
       <p id="rfc.section.3.2.p.6">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status code, then
-         the If-None-Match header field <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity-tags and Last-Modified Dates">Section&nbsp;2.4</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.)
+         the If-None-Match header field <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity-tags and Last-Modified Dates">Section&nbsp;2.2.4</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.)
       </p>
       <p id="rfc.section.3.2.p.7">Examples:</p>
-      <div id="rfc.figure.u.13"></div><pre class="text">  If-None-Match: "xyzzy"
+      <div id="rfc.figure.u.12"></div><pre class="text">  If-None-Match: "xyzzy"
   If-None-Match: W/"xyzzy"
   If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
@@ -982 +990 @@
          the time specified in this field, then do not perform the request method; instead, respond as detailed below.
       </p>
-      <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.8"></span>  <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a>
+      <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.8"></span>  <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a>
 </pre><p id="rfc.section.3.3.p.3">An example of the field is:</p>
-      <div id="rfc.figure.u.15"></div><pre class="text">  If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
+      <div id="rfc.figure.u.14"></div><pre class="text">  If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
 </pre><p id="rfc.section.3.3.p.5">A GET method with an If-Modified-Since header field and no Range header field requests that the selected representation be
          transferred only if it has been modified since the date given by the If-Modified-Since header field. The algorithm for determining
@@ -1002 +1010 @@
       <p id="rfc.section.3.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p>
       <ul class="empty">
-         <li> <b>Note:</b> The Range header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.4"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details.
+         <li> <b>Note:</b> The Range header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 5.4</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> for full details.
          </li>
          <li> <b>Note:</b> If-Modified-Since times are interpreted by the server, whose clock might not be synchronized with the client.
@@ -1030 +1038 @@
          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.
       </p>
-      <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a>
+      <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.9"></span>  <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a>
 </pre><p id="rfc.section.3.4.p.3">An example of the field is:</p>
-      <div id="rfc.figure.u.17"></div><pre class="text">  If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
+      <div id="rfc.figure.u.16"></div><pre class="text">  If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
 </pre><p id="rfc.section.3.4.p.5">If the request normally (i.e., without the If-Unmodified-Since header field) would result in anything other than a 2xx or
          412 status code, the If-Unmodified-Since header field <em class="bcp14">SHOULD</em> be ignored.
@@ -1040 +1048 @@
       <p id="rfc.section.3.4.p.7">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since
          header fields is undefined by this specification.
+      </p>
+      <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="header.if-range" href="#header.if-range">If-Range</a></h2>
+      <p id="rfc.section.3.5.p.1">The If-Range header field provides a special conditional request mechanism that is similar to If-Match and If-Unmodified-Since
+         but specific to HTTP range requests. If-Range is defined in <a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>.
       </p>
       <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="status.code.definitions" href="#status.code.definitions">Status Code Definitions</a></h1>
@@ -1120 +1132 @@
                   <td class="left">http</td>
                   <td class="left">standard</td>
-                  <td class="left"> <a href="#header.etag" id="rfc.xref.header.etag.2" title="ETag">Section&nbsp;2.2.1</a> 
+                  <td class="left"> <a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;2.2</a> 
                   </td>
                </tr>
@@ -1127 +1139 @@
                   <td class="left">http</td>
                   <td class="left">standard</td>
-                  <td class="left"> <a href="#header.if-match" id="rfc.xref.header.if-match.2" title="If-Match">Section&nbsp;3.1</a> 
+                  <td class="left"> <a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section&nbsp;3.1</a> 
                   </td>
                </tr>
@@ -1141 +1153 @@
                   <td class="left">http</td>
                   <td class="left">standard</td>
-                  <td class="left"> <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">Section&nbsp;3.2</a> 
+                  <td class="left"> <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section&nbsp;3.2</a> 
                   </td>
                </tr>
@@ -1240 +1252 @@
       </div>
       <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1>
-      <p id="rfc.section.A.p.1">Allow weak entity-tags in all requests except range requests (Sections <a href="#weak.and.strong.validators" title="Weak and Strong Validators">2.3</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.3" title="If-None-Match">3.2</a>).
+      <p id="rfc.section.A.p.1">Allow weak entity-tags in all requests except range requests (Sections <a href="#weak.and.strong.validators" title="Weak versus Strong">2.2.2</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">3.2</a>).
       </p>
       <p id="rfc.section.A.p.2">Change ABNF productions for header fields to only define the field value. (<a href="#header.fields" title="Precondition Header Fields">Section&nbsp;3</a>)
       </p>
       <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1>
-      <div id="rfc.figure.u.18"></div> <pre class="inline"><a href="#header.etag" class="smpl">ETag</a> = entity-tag
+      <div id="rfc.figure.u.17"></div> <pre class="inline"><a href="#header.etag" class="smpl">ETag</a> = entity-tag
 
 <a href="#notation" class="smpl">HTTP-date</a> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
@@ -1260 +1272 @@
 <a href="#notation" class="smpl">OWS</a> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
 
-<a href="#entity.tags" class="smpl">entity-tag</a> = [ weak ] opaque-tag
-
-<a href="#entity.tags" class="smpl">opaque-tag</a> = quoted-string
+<a href="#header.etag" class="smpl">entity-tag</a> = [ weak ] opaque-tag
+
+<a href="#header.etag" class="smpl">opaque-tag</a> = quoted-string
 
 <a href="#notation" class="smpl">quoted-string</a> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
 
-<a href="#entity.tags" class="smpl">weak</a> = %x57.2F ; W/
-</pre> <div id="rfc.figure.u.19"></div>
+<a href="#header.etag" class="smpl">weak</a> = %x57.2F ; W/
+</pre> <div id="rfc.figure.u.18"></div>
       <p>ABNF diagnostics:</p><pre class="inline">; ETag defined but not used
 ; If-Match defined but not used
@@ -1392 +1404 @@
             </li>
             <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul>
-                  <li>ETag header field&nbsp;&nbsp;<a href="#rfc.xref.header.etag.1">2.2</a>, <a href="#rfc.iref.e.1"><b>2.2.1</b></a>, <a href="#rfc.xref.header.etag.2">5.2</a></li>
+                  <li>ETag header field&nbsp;&nbsp;<a href="#rfc.iref.e.1"><b>2.2</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a></li>
                </ul>
             </li>
@@ -1398 +1410 @@
                   <li><tt>Grammar</tt>&nbsp;&nbsp;
                      <ul>
-                        <li><tt>entity-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2.2</b></a></li>
-                        <li><tt>ETag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>2.2.1</b></a></li>
+                        <li><tt>entity-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>2.2</b></a></li>
+                        <li><tt>ETag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2.2</b></a></li>
                         <li><tt>If-Match</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>3.1</b></a></li>
                         <li><tt>If-Modified-Since</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>3.3</b></a></li>
@@ -1405 +1417 @@
                         <li><tt>If-Unmodified-Since</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>3.4</b></a></li>
                         <li><tt>Last-Modified</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2.1</b></a></li>
-                        <li><tt>opaque-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>2.2</b></a></li>
-                        <li><tt>weak</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>2.2</b></a></li>
+                        <li><tt>opaque-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>2.2</b></a></li>
+                        <li><tt>weak</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>2.2</b></a></li>
                      </ul>
                   </li>
@@ -1414 +1426 @@
                   <li>Header Fields&nbsp;&nbsp;
                      <ul>
-                        <li>ETag&nbsp;&nbsp;<a href="#rfc.xref.header.etag.1">2.2</a>, <a href="#rfc.iref.h.2"><b>2.2.1</b></a>, <a href="#rfc.xref.header.etag.2">5.2</a></li>
-                        <li>If-Match&nbsp;&nbsp;<a href="#rfc.xref.header.if-match.1">2.2</a>, <a href="#rfc.iref.h.3"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.2">5.2</a></li>
+                        <li>ETag&nbsp;&nbsp;<a href="#rfc.iref.h.2"><b>2.2</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a></li>
+                        <li>If-Match&nbsp;&nbsp;<a href="#rfc.iref.h.3"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.1">5.2</a></li>
                         <li>If-Modified-Since&nbsp;&nbsp;<a href="#rfc.iref.h.5"><b>3.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">5.2</a></li>
-                        <li>If-None-Match&nbsp;&nbsp;<a href="#rfc.xref.header.if-none-match.1">2.2</a>, <a href="#rfc.iref.h.4"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.2">5.2</a>, <a href="#rfc.xref.header.if-none-match.3">A</a></li>
+                        <li>If-None-Match&nbsp;&nbsp;<a href="#rfc.iref.h.4"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.1">5.2</a>, <a href="#rfc.xref.header.if-none-match.2">A</a></li>
                         <li>If-Unmodified-Since&nbsp;&nbsp;<a href="#rfc.iref.h.6"><b>3.4</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">5.2</a></li>
                         <li>Last-Modified&nbsp;&nbsp;<a href="#rfc.iref.h.1"><b>2.1</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li>
@@ -1425 +1437 @@
             </li>
             <li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul>
-                  <li>If-Match header field&nbsp;&nbsp;<a href="#rfc.xref.header.if-match.1">2.2</a>, <a href="#rfc.iref.i.1"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.2">5.2</a></li>
+                  <li>If-Match header field&nbsp;&nbsp;<a href="#rfc.iref.i.1"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.1">5.2</a></li>
                   <li>If-Modified-Since header field&nbsp;&nbsp;<a href="#rfc.iref.i.3"><b>3.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">5.2</a></li>
-                  <li>If-None-Match header field&nbsp;&nbsp;<a href="#rfc.xref.header.if-none-match.1">2.2</a>, <a href="#rfc.iref.i.2"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.2">5.2</a>, <a href="#rfc.xref.header.if-none-match.3">A</a></li>
+                  <li>If-None-Match header field&nbsp;&nbsp;<a href="#rfc.iref.i.2"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.1">5.2</a>, <a href="#rfc.xref.header.if-none-match.2">A</a></li>
                   <li>If-Unmodified-Since header field&nbsp;&nbsp;<a href="#rfc.iref.i.4"><b>3.4</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">5.2</a></li>
                </ul>
@@ -1440 +1452 @@
             </li>
             <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
-                  <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">2.2.2</a>, <a href="#rfc.xref.Part1.6">4.1</a>, <a href="#rfc.xref.Part1.7">4.1</a>, <a href="#rfc.xref.Part1.8">6</a>, <a href="#Part1"><b>8.1</b></a><ul>
+                  <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">2.2.5</a>, <a href="#rfc.xref.Part1.6">4.1</a>, <a href="#rfc.xref.Part1.7">4.1</a>, <a href="#rfc.xref.Part1.8">6</a>, <a href="#Part1"><b>8.1</b></a><ul>
                         <li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">1.2</a></li>
                         <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>
                         <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.4">1.2</a></li>
-                        <li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">2.2.2</a></li>
+                        <li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">2.2.5</a></li>
                         <li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.6">4.1</a></li>
                         <li><em>Section 9.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">4.1</a></li>
                      </ul>
                   </li>
-                  <li><em>Part3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.2.2</a>, <a href="#rfc.xref.Part3.2">2.2.2</a>, <a href="#Part3"><b>8.1</b></a><ul>
-                        <li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.2.2</a></li>
-                        <li><em>Section 6.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.2">2.2.2</a></li>
+                  <li><em>Part3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.2.5</a>, <a href="#rfc.xref.Part3.2">2.2.5</a>, <a href="#Part3"><b>8.1</b></a><ul>
+                        <li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">2.2.5</a></li>
+                        <li><em>Section 6.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.2">2.2.5</a></li>
                      </ul>
                   </li>
-                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.2</a>, <a href="#rfc.xref.Part5.2">2.3</a>, <a href="#rfc.xref.Part5.3">2.3</a>, <a href="#rfc.xref.Part5.4">3.3</a>, <a href="#Part5"><b>8.1</b></a><ul>
-                        <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">2.2</a></li>
-                        <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.4">3.3</a></li>
+                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">3.3</a>, <a href="#rfc.xref.Part5.2">3.5</a>, <a href="#Part5"><b>8.1</b></a><ul>
+                        <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.2">3.5</a></li>
+                        <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">3.3</a></li>
                      </ul>
                   </li>
-                  <li><em>Part6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">1</a>, <a href="#Part6"><b>8.1</b></a></li>
+                  <li><em>Part6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">1</a>, <a href="#rfc.xref.Part6.2">2.1.1</a>, <a href="#rfc.xref.Part6.3">2.2.1</a>, <a href="#Part6"><b>8.1</b></a></li>
                </ul>
             </li>

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

@@ -221 +221 @@
    specify preconditions to be checked before performing the action
    given by the request method.  Conditional GET requests are the most
-   efficient mechanism for HTTP cache updates &caching;.  Conditionals can be
+   efficient mechanism for HTTP cache updates &caching;.  Conditionals
+   can also be
    applied to state-changing methods, such as PUT and DELETE, to prevent
    the "lost update" problem: one client accidentally overwriting
@@ -313 +314 @@
    has been defined by various extensions of HTTP, such as WebDAV
    <xref target="RFC4918"/>, that are beyond the scope of this specification.
-   Such metadata is referred to as a "<x:dfn>validator</x:dfn>" when it is
-   used within a precondition.
+   A resource metadata value is referred to as a "<x:dfn>validator</x:dfn>"
+   when it is used within a precondition.
 </t>
 
@@ -323 +324 @@
 <t>
    The "Last-Modified" header field indicates the date and time at
-   which the origin server believes the representation was last modified.
+   which the origin server believes the selected representation was
+   last modified.
 </t>
 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Last-Modified"/>
@@ -334 +336 @@
   Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
 </artwork></figure>
+
+<section title="Generation" anchor="lastmod.generation">
+<t>
+   Origin servers &SHOULD; send Last-Modified for any selected
+   representation for which a last modification date can be reasonably
+   and consistently determined, since its use in conditional requests
+   and evaluating cache freshness (&caching;) results in a substantial
+   reduction of HTTP traffic on the Internet and can be a significant
+   factor in improving service scalability and reliability.
+</t>
 <t>
    A representation is typically the sum of many parts behind the
@@ -345 +357 @@
 </t>
 <t>
-   An origin server &MUST-NOT; send a Last-Modified date which is later
-   than the server's time of message origination. In such cases, where
-   the resource's last modification would indicate some time in the
-   future, the server &MUST; replace that date with the message
-   origination date.
-</t>
-<t>
-   An origin server &SHOULD; obtain the Last-Modified value of the representation
-   as close as possible to the time that it generates the Date value of
-   its response. This allows a recipient to make an accurate assessment
-   of the representation's modification time, especially if the representation changes
-   near the time that the response is generated.
-</t>
-<t>
-   HTTP/1.1 servers &SHOULD; send Last-Modified whenever feasible.
-</t>
-<t>
-   The Last-Modified header field value is often used as a cache
-   validator. In simple terms, a cache entry is considered to be valid
-   if the representation has not been modified since the Last-Modified value.
-</t>
-</section>
-
-<section title="Entity Tags" anchor="entity.tags">
+   An origin server &SHOULD; obtain the Last-Modified value of the
+   representation as close as possible to the time that it generates
+   the Date field-value for its response. This allows a recipient to
+   make an accurate assessment of the representation's modification time,
+   especially if the representation changes near the time that the
+   response is generated.
+</t>
+<t>
+   An origin server with a clock &MUST-NOT; send a Last-Modified date
+   that is later than the server's time of message origination (Date).
+   If the last modification time is derived from implementation-specific
+   metadata that evaluates to some time in the future, according to the
+   origin server's clock, then the origin server &MUST; replace that
+   value with the message origination date. This prevents a future
+   modification date from having an adverse impact on cache validation.
+</t>
+</section>
+
+<section title="Comparison" anchor="lastmod.comparison">
+<t>
+   A Last-Modified time, when used as a validator in a request, is
+   implicitly weak unless it is possible to deduce that it is strong,
+   using the following rules:
+  <list style="symbols">
+     <t>The validator is being compared by an origin server to the
+        actual current validator for the representation and,</t>
+     <t>That origin server reliably knows that the associated representation did
+        not change twice during the second covered by the presented
+        validator.</t>
+  </list>
+</t>
+<t>
+   or
+  <list style="symbols">
+     <t>The validator is about to be used by a client in an If-Modified-Since
+        or If-Unmodified-Since header field, because the client
+        has a cache entry for the associated representation, and</t>
+     <t>That cache entry includes a Date value, which gives the time
+        when the origin server sent the original response, and</t>
+     <t>The presented Last-Modified time is at least 60 seconds before
+        the Date value.</t>
+  </list>
+</t>
+<t>
+   or
+  <list style="symbols">
+     <t>The validator is being compared by an intermediate cache to the
+        validator stored in its cache entry for the representation, and</t>
+     <t>That cache entry includes a Date value, which gives the time
+        when the origin server sent the original response, and</t>
+     <t>The presented Last-Modified time is at least 60 seconds before
+        the Date value.</t>
+  </list>
+</t>
+<t>
+   This method relies on the fact that if two different responses were
+   sent by the origin server during the same second, but both had the
+   same Last-Modified time, then at least one of those responses would
+   have a Date value equal to its Last-Modified time. The arbitrary 60-second
+   limit guards against the possibility that the Date and Last-Modified
+   values are generated from different clocks, or at somewhat
+   different times during the preparation of the response. An
+   implementation &MAY; use a value larger than 60 seconds, if it is
+   believed that 60 seconds is too short.
+</t>
+</section>
+</section>
+
+<section title="ETag" anchor="header.etag">
+  <iref primary="true" item="ETag header field" x:for-anchor=""/>
+  <iref primary="true" item="Header Fields" subitem="ETag" x:for-anchor=""/>
+  <x:anchor-alias value="ETag"/>
   <x:anchor-alias value="entity-tag"/>
+  <x:anchor-alias value="entity.tags"/>
   <x:anchor-alias value="opaque-tag"/>
   <x:anchor-alias value="weak"/>
 <t>
-   Entity-tags are used for comparing two or more representations of the same
-   resource. HTTP/1.1 uses entity-tags in the ETag (<xref target="header.etag"/>),
-   If-Match (<xref target="header.if-match"/>), If-None-Match (<xref target="header.if-none-match"/>), and
-   If-Range (&header-if-range;) header fields. The definition of how they
-   are used and compared as cache validators is in <xref target="weak.and.strong.validators"/>. An
-   entity-tag consists of an opaque quoted string, possibly prefixed by
-   a weakness indicator.
-</t>
-<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-tag"/><iref primary="true" item="Grammar" subitem="weak"/><iref primary="true" item="Grammar" subitem="opaque-tag"/>
+   The ETag header field provides the current entity-tag for the
+   selected representation.
+   An entity-tag is an opaque validator for differentiating between
+   multiple representations of the same resource, regardless of whether
+   those multiple representations are due to resource state changes over
+   time, content negotiation resulting in multiple representations being
+   valid at the same time, or both. An entity-tag consists of an opaque
+   quoted string, possibly prefixed by a weakness indicator.
+</t>
+<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="ETag"/><iref primary="true" item="Grammar" subitem="entity-tag"/><iref primary="true" item="Grammar" subitem="weak"/><iref primary="true" item="Grammar" subitem="opaque-tag"/>
+  <x:ref>ETag</x:ref>       = <x:ref>entity-tag</x:ref>
+
   <x:ref>entity-tag</x:ref> = [ <x:ref>weak</x:ref> ] <x:ref>opaque-tag</x:ref>
   <x:ref>weak</x:ref>       = <x:abnf-char-sequence>"W/"</x:abnf-char-sequence> ; "W/", case-sensitive
@@ -387 +451 @@
 </artwork></figure>
 <t>
-   A "strong entity-tag" &MAY; be shared by two representations of a resource
-   only if they are equivalent by octet equality.
-</t>
-<t>
-   A "weak entity-tag", indicated by the "W/" prefix, &MAY; be shared by
-   two representations of a resource. A weak entity-tag can only be used
-   for weak comparison.
-</t>
-<t>
-   Cache entries might persist for arbitrarily long periods, regardless
-   of expiration times, so it is inappropriate to expect that a cache will
-   never again attempt to validate an entry using a validator that it
-   obtained at some point in the past.
-   A strong entity-tag &MUST; be unique across all versions of all
-   representations associated with a particular resource over time.
-   However, there is no implication of uniqueness across entity-tags
-   of different resources (i.e., the same entity-tag value might be
-   in use for representations of multiple resources at the same time
-   and does not imply that those representations are equivalent).
-</t>
-
-<section title="ETag" anchor="header.etag">
-  <iref primary="true" item="ETag header field" x:for-anchor=""/>
-  <iref primary="true" item="Header Fields" subitem="ETag" x:for-anchor=""/>
-  <x:anchor-alias value="ETag"/>
-<t>
-   The "ETag" header field provides the current value of the
-   entity-tag (see <xref target="entity.tags"/>) for one representation of
-   the target resource.  An entity-tag
-   is intended for use as a resource-local identifier for differentiating
-   between representations of the same resource that vary over time or via
-   content negotiation (see <xref target="weak.and.strong.validators"/>).
-</t>
-<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="ETag"/>
-  <x:ref>ETag</x:ref> = <x:ref>entity-tag</x:ref>
-</artwork></figure>
+   An entity-tag can be more reliable for validation than a modification
+   date in situations where it is inconvenient to store modification
+   dates, where the one-second resolution of HTTP date values is not
+   sufficient, or where modification dates are not consistently maintained.
+</t>
 <figure><preamble>
   Examples:
@@ -431 +464 @@
   ETag: ""
 </artwork></figure>
-<t>
-   An entity-tag provides an "opaque" cache validator that allows for
-   more reliable validation than modification dates in situations where
-   it is inconvenient to store modification dates,
-   where the one-second resolution of HTTP date values is not
-   sufficient, or where the origin server wishes to avoid certain
-   paradoxes that might arise from the use of modification dates.
-</t>
+
+<section title="Generation" anchor="entity.tag.generation">
 <t>
    The principle behind entity-tags is that only the service author
-   knows the semantics of a resource well enough to select an
-   appropriate cache validation mechanism, and the specification of any
-   validator comparison function more complex than byte-equality would
-   open up a can of worms. Thus, comparisons of any other header fields
-   (except Last-Modified, for compatibility with HTTP/1.0) are never
-   used for purposes of validating a cache entry.
-</t>
-</section>
-
-<section title="Example: Entity-tags varying on Content-Negotiated Resources" anchor="example.entity.tag.vs.conneg">
-<t>
-   Consider a resource that is subject to content negotiation (&content-negotiation;),
-   and where the representations returned upon a GET request vary based on
-   the Accept-Encoding request header field (&header-accept-encoding;):
-</t>
-<figure><preamble>>> Request:</preamble><artwork type="message/http; msgtype=&#34;request&#34;"  x:indent-with="  ">
-GET /index HTTP/1.1
-Host: www.example.com
-Accept-Encoding: gzip
-
-</artwork></figure>
-<t>
-   In this case, the response might or might not use the gzip content coding.
-   If it does not, the response might look like:
-</t>
-<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
-HTTP/1.1 200 OK
-Date: Thu, 26 Mar 2010 00:05:00 GMT
-ETag: "123-a"
-Content-Length: <x:length-of target="exbody"/>
-Vary: Accept-Encoding
-Content-Type: text/plain
-
-<x:span anchor="exbody">Hello World!
-Hello World!
-Hello World!
-Hello World!
-Hello World!
-</x:span></artwork></figure>
-<t>
-   An alternative representation that does use gzip content coding would be:
-</t>
-<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
-HTTP/1.1 200 OK
-Date: Thu, 26 Mar 2010 00:05:00 GMT
-ETag: "123-b"
-Content-Length: 43
-Vary: Accept-Encoding
-Content-Type: text/plain
-Content-Encoding: gzip
-
-<spanx>...binary data...</spanx></artwork></figure>
-<x:note>
-  <t>
-    <x:h>Note:</x:h> Content codings are a property of the representation,
-    so therefore an entity-tag of an encoded representation must be distinct
-    from an unencoded representation to prevent conflicts during cache updates
-    and range requests.  In contrast, transfer codings (&transfer-codings;)
-    apply only during message transfer and do not require distinct entity-tags.
-  </t>
-</x:note>
-</section>
-</section>
-
-<section title="Weak and Strong Validators" anchor="weak.and.strong.validators">
+   knows the implementation of a resource well enough to select the
+   most accurate and efficient validation mechanism for that resource,
+   and that any such mechanism can be mapped to a simple sequence of
+   octets for easy comparison.  Since the value is opaque, there is no
+   need for the client to be aware of how each entity-tag is constructed.
+</t>
+<t>
+   For example, a resource that has implementation-specific versioning
+   applied to all changes might use an internal revision number, perhaps
+   combined with a variance identifier for content negotiation, to
+   accurately differentiate between representations.
+   Other implementations might use a stored hash of representation content,
+   a combination of various filesystem attributes, or a modification
+   timestamp that has sub-second resolution.
+</t>
+<t>
+   Origin servers &SHOULD; send ETag for any selected representation
+   for which detection of changes can be reasonably and consistently
+   determined, since the entity-tag's use in conditional requests and
+   evaluating cache freshness (&caching;) can result in a substantial
+   reduction of HTTP network traffic and can be a significant factor in
+   improving service scalability and reliability.
+</t>
+</section>
+
+<section title="Weak versus Strong" anchor="weak.and.strong.validators">
 <t>
    Since both origin servers and caches will compare two validators to
-   decide if they represent the same or different representations, one
+   decide if they indicate the same or different representations, one
    normally would expect that if the representation (including both
    representation header fields and representation body) changes in any
    way, then the associated validator would change as well. If this is
-   true, then we call this validator a "strong validator".  One example
+   true, then we call that validator a "strong validator".  One example
    of a strong validator is an integer that is incremented in stable
    storage every time a representation is changed.
@@ -529 +517 @@
 </t>
 <t>
+   One can think of a strong validator as part of an identifier for a
+   specific representation, whereas a weak validator is part of an
+   identifier for a set of equivalent representations (where this notion
+   of equivalence is entirely governed by the origin server and beyond
+   the scope of this specification).
+</t>
+<t>
    An entity-tag is normally a strong validator, but the protocol
-   provides a mechanism to tag an entity-tag as "weak". One can think
-   of a strong validator as part of an identifier for a specific
-   representation, whereas a weak validator is part of an identifier
-   for a set of equivalent representations (where this notion of
-   equivalence is entirely governed by the origin server and beyond
-   the scope of this specification).
+   provides a mechanism to tag an entity-tag as "weak". 
   <list><t>
       A representation's modification time, if defined with only one-second
@@ -556 +546 @@
 </t>
 <t>
-   A "use" of a validator is either when a client generates a request
-   and includes the validator in a validating header field, or when a
-   server compares two validators.
-</t>
-<t>
-   Strong validators are usable in any context. Weak validators are only
-   usable in contexts that do not depend on exact equality of a representation.
-   For example, either kind is usable for a normal conditional GET.
-   However, only a strong validator is usable for range retrieval
-   (<xref target="Part5"/>), since otherwise the client might end up
-   with an internally inconsistent representation.
-   Clients &MUST-NOT; use weak validators in range requests.
-</t>
-<t>
-   The only function that HTTP/1.1 defines on validators is
-   comparison. There are two validator comparison functions, depending
+   A "strong entity-tag" &MAY; be shared by two representations of a resource
+   only if they are equivalent by octet equality.
+</t>
+<t>
+   A "weak entity-tag", indicated by the "W/" prefix, &MAY; be shared by
+   two representations of a resource. A weak entity-tag can only be used
+   for weak comparison.
+</t>
+<t>
+   Cache entries might persist for arbitrarily long periods, regardless
+   of expiration times.  Thus, a cache might attempt to validate an
+   entry using a validator that it obtained in the distant past.
+   A strong entity-tag &MUST; be unique across all versions of all
+   representations associated with a particular resource over time.
+   However, there is no implication of uniqueness across entity-tags
+   of different resources (i.e., the same entity-tag value might be
+   in use for representations of multiple resources at the same time
+   and does not imply that those representations are equivalent).
+</t>
+</section>
+
+<section title="Comparison" anchor="entity.tag.comparison">
+  <x:anchor-alias value="validator.comparison"/>
+<t>
+   There are two entity-tag comparison functions, depending
    on whether the comparison context allows the use of weak validators
    or not:
@@ -585 +584 @@
 </t>
 <t>
+   A "use" of a validator is either when a client generates a request
+   and includes the validator in a precondition, or when a server
+   compares two validators.
+</t>
+<t>
+   Strong validators are usable in any context. Weak validators are only
+   usable in contexts that do not depend on exact equality of a representation.
+   For example, either kind is usable for a normal conditional GET.
+</t>
+<t>
    The example below shows the results for a set of entity-tag pairs,
    and both the weak and strong comparison function results:
@@ -616 +625 @@
 <t>
    An entity-tag is strong unless it is explicitly tagged as weak.
-   <xref target="entity.tags"/> gives the syntax for entity-tags.
-</t>
-<t>
-   A Last-Modified time, when used as a validator in a request, is
-   implicitly weak unless it is possible to deduce that it is strong,
-   using the following rules:
-  <list style="symbols">
-     <t>The validator is being compared by an origin server to the
-        actual current validator for the representation and,</t>
-     <t>That origin server reliably knows that the associated representation did
-        not change twice during the second covered by the presented
-        validator.</t>
-  </list>
-</t>
-<t>
-   or
-  <list style="symbols">
-     <t>The validator is about to be used by a client in an If-Modified-Since
-        or If-Unmodified-Since header field, because the client
-        has a cache entry for the associated representation, and</t>
-     <t>That cache entry includes a Date value, which gives the time
-        when the origin server sent the original response, and</t>
-     <t>The presented Last-Modified time is at least 60 seconds before
-        the Date value.</t>
-  </list>
-</t>
-<t>
-   or
-  <list style="symbols">
-     <t>The validator is being compared by an intermediate cache to the
-        validator stored in its cache entry for the representation, and</t>
-     <t>That cache entry includes a Date value, which gives the time
-        when the origin server sent the original response, and</t>
-     <t>The presented Last-Modified time is at least 60 seconds before
-        the Date value.</t>
-  </list>
-</t>
-<t>
-   This method relies on the fact that if two different responses were
-   sent by the origin server during the same second, but both had the
-   same Last-Modified time, then at least one of those responses would
-   have a Date value equal to its Last-Modified time. The arbitrary 60-second
-   limit guards against the possibility that the Date and Last-Modified
-   values are generated from different clocks, or at somewhat
-   different times during the preparation of the response. An
-   implementation &MAY; use a value larger than 60 seconds, if it is
-   believed that 60 seconds is too short.
-</t>
-<t>
-   If a client wishes to perform a sub-range retrieval on a value for
-   which it has only a Last-Modified time and no opaque validator, it
-   &MAY; do this only if the Last-Modified time is strong in the sense
-   described here.
-</t>
-<t>
-   A cache or origin server receiving a conditional range request
-   (<xref target="Part5"/>) &MUST; use the strong comparison function to
-   evaluate the condition.
-</t>
-<t>
-   These rules allow HTTP/1.1 caches and clients to safely perform sub-range
-   retrievals on values that have been obtained from HTTP/1.0
-   servers.
 </t>
 </section>
@@ -760 +706 @@
 </section>
 
+<section title="Example: Entity-tags varying on Content-Negotiated Resources" anchor="example.entity.tag.vs.conneg">
+<t>
+   Consider a resource that is subject to content negotiation (&content-negotiation;),
+   and where the representations returned upon a GET request vary based on
+   the Accept-Encoding request header field (&header-accept-encoding;):
+</t>
+<figure><preamble>>> Request:</preamble><artwork type="message/http; msgtype=&#34;request&#34;"  x:indent-with="  ">
+GET /index HTTP/1.1
+Host: www.example.com
+Accept-Encoding: gzip
+
+</artwork></figure>
+<t>
+   In this case, the response might or might not use the gzip content coding.
+   If it does not, the response might look like:
+</t>
+<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
+HTTP/1.1 200 OK
+Date: Thu, 26 Mar 2010 00:05:00 GMT
+ETag: "123-a"
+Content-Length: <x:length-of target="exbody"/>
+Vary: Accept-Encoding
+Content-Type: text/plain
+
+<x:span anchor="exbody">Hello World!
+Hello World!
+Hello World!
+Hello World!
+Hello World!
+</x:span></artwork></figure>
+<t>
+   An alternative representation that does use gzip content coding would be:
+</t>
+<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
+HTTP/1.1 200 OK
+Date: Thu, 26 Mar 2010 00:05:00 GMT
+ETag: "123-b"
+Content-Length: 43
+Vary: Accept-Encoding
+Content-Type: text/plain
+Content-Encoding: gzip
+
+<spanx>...binary data...</spanx></artwork></figure>
+<x:note>
+  <t>
+    <x:h>Note:</x:h> Content codings are a property of the representation,
+    so therefore an entity-tag of an encoded representation must be distinct
+    from an unencoded representation to prevent conflicts during cache updates
+    and range requests.  In contrast, transfer codings (&transfer-codings;)
+    apply only during message transfer and do not require distinct entity-tags.
+  </t>
+</x:note>
+</section>
+</section>
 </section>
 
@@ -1006 +1006 @@
    field and either an If-None-Match or an If-Modified-Since header
    fields is undefined by this specification.
+</t>
+</section>
+
+<section title="If-Range" anchor="header.if-range">
+<t>
+   The If-Range header field provides a special conditional request
+   mechanism that is similar to If-Match and If-Unmodified-Since but
+   specific to HTTP range requests. If-Range is defined in &header-if-range;.
 </t>
 </section>

draft-ietf-httpbis/latest/p5-range.html

@@ -359 +359 @@
   } 
   @bottom-center {
-       content: "Expires October 6, 2011"; 
+       content: "Expires October 7, 2011"; 
   } 
   @bottom-right {
@@ -406 +406 @@
       <meta name="dct.creator" content="Reschke, J. F.">
       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p5-range-latest">
-      <meta name="dct.issued" scheme="ISO8601" content="2011-04-04">
+      <meta name="dct.issued" scheme="ISO8601" content="2011-04-05">
       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
       <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 5 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 5 defines range-specific requests and the rules for constructing and combining responses to those requests.">
@@ -432 +432 @@
             </tr>
             <tr>
-               <td class="left">Expires: October 6, 2011</td>
+               <td class="left">Expires: October 7, 2011</td>
                <td class="right">J. Mogul</td>
             </tr>
@@ -489 +489 @@
             <tr>
                <td class="left"></td>
-               <td class="right">April 4, 2011</td>
+               <td class="right">April 5, 2011</td>
             </tr>
          </tbody>
@@ -515 +515 @@
          in progress”.
       </p>
-      <p>This Internet-Draft will expire on October 6, 2011.</p>
+      <p>This Internet-Draft will expire on October 7, 2011.</p>
       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
       <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
@@ -642 +642 @@
       <p id="rfc.section.1.2.2.p.1">The ABNF rules below are defined in other parts:</p>
       <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;
-</pre><div id="rfc.figure.u.3"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">entity-tag</a> = &lt;entity-tag, defined in <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#entity.tags" title="Entity Tags">Section 2.2</a>&gt;
+</pre><div id="rfc.figure.u.3"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">entity-tag</a> = &lt;entity-tag, defined in <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#header.etag" title="ETag">Section 2.2</a>&gt;
 </pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="range.units" href="#range.units">Range Units</a></h1>
-      <p id="rfc.section.2.p.1">HTTP/1.1 allows a client to request that only part (a range of) the representation be included within the response. HTTP/1.1
+      <p id="rfc.section.2.p.1">HTTP/1.1 allows a client to request that only part (a range) of the representation be included within the response. HTTP/1.1
          uses range units in the Range (<a href="#header.range" id="rfc.xref.header.range.1" title="Range">Section&nbsp;5.4</a>) and Content-Range (<a href="#header.content-range" id="rfc.xref.header.content-range.1" title="Content-Range">Section&nbsp;5.2</a>) header fields. A representation can be broken down into subranges according to various structural units.
       </p>
@@ -656 +656 @@
       </p>
       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="range.specifier.registry" href="#range.specifier.registry">Range Specifier Registry</a></h2>
-      <p id="rfc.section.2.1.p.1">The HTTP Ranger Specifier Registry defines the name space for the range specifier names.</p>
+      <p id="rfc.section.2.1.p.1">The HTTP Range Specifier Registry defines the name space for the range specifier names.</p>
       <p id="rfc.section.2.1.p.2">Registrations <em class="bcp14">MUST</em> include the following fields: 
       </p>
@@ -712 +712 @@
       <ul>
          <li>Both the incoming response and the cache entry have a cache validator.</li>
-         <li>The two cache validators match using the strong comparison function (see <a href="p4-conditional.html#weak.and.strong.validators" title="Weak and Strong Validators">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
+         <li>The two cache validators match using the strong comparison function (see <a href="p4-conditional.html#weak.and.strong.validators" title="Weak versus Strong">Section 2.2.2</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
          </li>
       </ul>
@@ -827 +827 @@
       </p>
       <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.11"></span>  <a href="#header.if-range" class="smpl">If-Range</a> = <a href="#abnf.dependencies" class="smpl">entity-tag</a> / <a href="#abnf.dependencies" class="smpl">HTTP-date</a>
-</pre><p id="rfc.section.5.3.p.4">If the client has no entity-tag for a representation, but does have a Last-Modified date, it <em class="bcp14">MAY</em> use that date in an If-Range header field. (The server can distinguish between a valid HTTP-date and any form of entity-tag
+</pre><p id="rfc.section.5.3.p.4">Only a strong validator (<a href="p4-conditional.html#weak.and.strong.validators" title="Weak versus Strong">Section 2.2.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>) is usable for range retrieval, since otherwise the client might end up with an internally inconsistent representation. Clients <em class="bcp14">MUST NOT</em> use weak validators in range requests. A cache or origin server receiving a conditional range request <em class="bcp14">MUST</em> use the strong comparison function to evaluate the condition.
+      </p>
+      <p id="rfc.section.5.3.p.5">If the client has no entity-tag for a representation, but does have a Last-Modified date, it <em class="bcp14">MAY</em> use that date in an If-Range header field. (The server can distinguish between a valid HTTP-date and any form of entity-tag
          by examining no more than two characters.) The If-Range header field <em class="bcp14">SHOULD</em> only be used together with a Range header field, and <em class="bcp14">MUST</em> be ignored if the request does not include a Range header field, or if the server does not support the sub-range operation.
       </p>
-      <p id="rfc.section.5.3.p.5">If the entity-tag given in the If-Range header field matches the current cache validator for the representation, then the
+      <p id="rfc.section.5.3.p.6">If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator,
+         it <em class="bcp14">MAY</em> do this only if the Last-Modified time is strong in the sense described in <a href="p4-conditional.html#lastmod.comparison" title="Comparison">Section 2.1.2</a> of <a href="#Part4" id="rfc.xref.Part4.4"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
+      </p>
+      <p id="rfc.section.5.3.p.7">If the entity-tag given in the If-Range header field matches the current cache validator for the representation, then the
          server <em class="bcp14">SHOULD</em> provide the specified sub-range of the representation using a 206 (Partial Content) response. If the cache validator does
          not match, then the server <em class="bcp14">SHOULD</em> return the entire representation using a 200 (OK) response.
@@ -1461 +1466 @@
                      </ul>
                   </li>
-                  <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">1.2.2</a>, <a href="#rfc.xref.Part4.2">4</a>, <a href="#Part4"><b>9.1</b></a><ul>
+                  <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">1.2.2</a>, <a href="#rfc.xref.Part4.2">4</a>, <a href="#rfc.xref.Part4.3">5.3</a>, <a href="#rfc.xref.Part4.4">5.3</a>, <a href="#Part4"><b>9.1</b></a><ul>
+                        <li><em>Section 2.1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.4">5.3</a></li>
                         <li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">1.2.2</a></li>
-                        <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.2">4</a></li>
+                        <li><em>Section 2.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.2">4</a>, <a href="#rfc.xref.Part4.3">5.3</a></li>
                      </ul>
                   </li>

draft-ietf-httpbis/latest/p5-range.xml

@@ -20 +20 @@
   <!ENTITY full-date                  "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
   <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
-  <!ENTITY entity-tags                "<xref target='Part4' x:rel='#entity.tags' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
+  <!ENTITY entity-tags                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
   <!ENTITY weak-and-strong-validators "<xref target='Part4' x:rel='#weak.and.strong.validators' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
+  <!ENTITY lastmod-comparison         "<xref target='Part4' x:rel='#lastmod.comparison' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
 ]>
 <?rfc toc="yes" ?>
@@ -313 +314 @@
   <x:anchor-alias value="range-unit"/>
 <t>
-   HTTP/1.1 allows a client to request that only part (a range of) the
+   HTTP/1.1 allows a client to request that only part (a range) of the
    representation be included within the response. HTTP/1.1 uses range
    units in the Range (<xref target="header.range"/>) and Content-Range (<xref target="header.content-range"/>)
@@ -339 +340 @@
 <section title="Range Specifier Registry" anchor="range.specifier.registry">
 <t>
-   The HTTP Ranger Specifier Registry defines the name space for the range
+   The HTTP Range Specifier Registry defines the name space for the range
    specifier names.
 </t>
@@ -678 +679 @@
 </artwork></figure>
 <t>
+   Only a strong validator (&weak-and-strong-validators;) is usable for
+   range retrieval, since otherwise the client might end up with an
+   internally inconsistent representation.
+   Clients &MUST-NOT; use weak validators in range requests.
+   A cache or origin server receiving a conditional range request
+   &MUST; use the strong comparison function to evaluate the condition.
+</t>
+<t>
    If the client has no entity-tag for a representation, but does have a Last-Modified
    date, it &MAY; use that date in an If-Range header field. (The
@@ -685 +694 @@
    ignored if the request does not include a Range header field, or if the
    server does not support the sub-range operation.
+</t>
+<t>
+   If a client wishes to perform a sub-range retrieval on a value for
+   which it has only a Last-Modified time and no opaque validator, it
+   &MAY; do this only if the Last-Modified time is strong in the sense
+   described in &lastmod-comparison;.
 </t>
 <t>

draft-ietf-httpbis/latest/p6-cache.html

@@ -362 +362 @@
   } 
   @bottom-center {
-       content: "Expires October 6, 2011"; 
+       content: "Expires October 7, 2011"; 
   } 
   @bottom-right {
@@ -408 +408 @@
       <meta name="dct.creator" content="Reschke, J. F.">
       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p6-cache-latest">
-      <meta name="dct.issued" scheme="ISO8601" content="2011-04-04">
+      <meta name="dct.issued" scheme="ISO8601" content="2011-04-05">
       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
       <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. This document is Part 6 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 6 defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages.">
@@ -434 +434 @@
             </tr>
             <tr>
-               <td class="left">Expires: October 6, 2011</td>
+               <td class="left">Expires: October 7, 2011</td>
                <td class="right">J. Mogul</td>
             </tr>
@@ -495 +495 @@
             <tr>
                <td class="left"></td>
-               <td class="right">April 4, 2011</td>
+               <td class="right">April 5, 2011</td>
             </tr>
          </tbody>
@@ -521 +521 @@
          in progress”.
       </p>
-      <p>This Internet-Draft will expire on October 6, 2011.</p>
+      <p>This Internet-Draft will expire on October 7, 2011.</p>
       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
       <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
@@ -1021 +1021 @@
       <p id="rfc.section.2.8.p.2">If the new response contains an ETag, it identifies the stored response to use. <span class="comment" id="TODO-mention-CL">[<a href="#TODO-mention-CL" class="smpl">TODO-mention-CL</a>: might need language about Content-Location here]</span><span class="comment" id="TODO-select-for-combine">[<a href="#TODO-select-for-combine" class="smpl">TODO-select-for-combine</a>: Shouldn't this be the selected response?]</span> 
       </p>
-      <p id="rfc.section.2.8.p.3">When the new response's status code is 206 (partial content), a cache <em class="bcp14">MUST NOT</em> combine it with the old response if either response does not have a validator, and <em class="bcp14">MUST NOT</em> combine it with the old response when those validators do not match with the strong comparison function (see <a href="p4-conditional.html#weak.and.strong.validators" title="Weak and Strong Validators">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
+      <p id="rfc.section.2.8.p.3">When the new response's status code is 206 (partial content), a cache <em class="bcp14">MUST NOT</em> combine it with the old response if either response does not have a validator, and <em class="bcp14">MUST NOT</em> combine it with the old response when those validators do not match with the strong comparison function (see <a href="p4-conditional.html#weak.and.strong.validators" title="Weak versus Strong">Section 2.2.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>).
       </p>
       <p id="rfc.section.2.8.p.4">The stored response header fields are used as those of the updated response, except that </p>
@@ -2094 +2094 @@
                   <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">2.3.1.1</a>, <a href="#rfc.xref.Part4.2">2.4</a>, <a href="#rfc.xref.Part4.3">2.8</a>, <a href="#Part4"><b>8.1</b></a><ul>
                         <li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">2.3.1.1</a></li>
-                        <li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">2.8</a></li>
+                        <li><em>Section 2.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">2.8</a></li>
                      </ul>
                   </li>

draft-ietf-httpbis/latest/p7-auth.html

@@ -359 +359 @@
   } 
   @bottom-center {
-       content: "Expires October 6, 2011"; 
+       content: "Expires October 7, 2011"; 
   } 
   @bottom-right {
@@ -404 +404 @@
       <meta name="dct.creator" content="Reschke, J. F.">
       <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p7-auth-latest">
-      <meta name="dct.issued" scheme="ISO8601" content="2011-04-04">
+      <meta name="dct.issued" scheme="ISO8601" content="2011-04-05">
       <meta name="dct.replaces" content="urn:ietf:rfc:2616">
       <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 7 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 7 defines HTTP Authentication.">
@@ -435 +435 @@
             </tr>
             <tr>
-               <td class="left">Expires: October 6, 2011</td>
+               <td class="left">Expires: October 7, 2011</td>
                <td class="right">HP</td>
             </tr>
@@ -488 +488 @@
             <tr>
                <td class="left"></td>
-               <td class="right">April 4, 2011</td>
+               <td class="right">April 5, 2011</td>
             </tr>
          </tbody>
@@ -514 +514 @@
          in progress”.
       </p>
-      <p>This Internet-Draft will expire on October 6, 2011.</p>
+      <p>This Internet-Draft will expire on October 7, 2011.</p>
       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
       <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p>