source: draft-ietf-httpbis/latest/p4-conditional.xml @ 1373

Last change on this file since 1373 was 1373, checked in by julian.reschke@…, 8 years ago

align sbatracts and put a paragraph break inside for readability

  • Property svn:eol-style set to native
File size: 70.7 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "August">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-date                "<xref target='Part1' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY clockless                  "<xref target='Part1' x:rel='#clockless.origin.server.operation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY full-date                  "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY transfer-codings           "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32]>
33<?rfc toc="yes" ?>
34<?rfc symrefs="yes" ?>
35<?rfc sortrefs="yes" ?>
36<?rfc compact="yes"?>
37<?rfc subcompact="no" ?>
38<?rfc linkmailto="no" ?>
39<?rfc editing="no" ?>
40<?rfc comments="yes"?>
41<?rfc inline="yes"?>
42<?rfc rfcedstyle="yes"?>
43<?rfc-ext allow-markup-in-artwork="yes" ?>
44<?rfc-ext include-references-in-index="yes" ?>
45<rfc obsoletes="2616" category="std" x:maturity-level="draft"
46     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"
47     xmlns:x='http://purl.org/net/xml2rfc/ext'>
48<front>
49
50  <title abbrev="HTTP/1.1, Part 4">HTTP/1.1, part 4: Conditional Requests</title>
51
52  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
53    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
54    <address>
55      <postal>
56        <street>345 Park Ave</street>
57        <city>San Jose</city>
58        <region>CA</region>
59        <code>95110</code>
60        <country>USA</country>
61      </postal>
62      <email>fielding@gbiv.com</email>
63      <uri>http://roy.gbiv.com/</uri>
64    </address>
65  </author>
66
67  <author initials="J." surname="Gettys" fullname="Jim Gettys">
68    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
69    <address>
70      <postal>
71        <street>21 Oak Knoll Road</street>
72        <city>Carlisle</city>
73        <region>MA</region>
74        <code>01741</code>
75        <country>USA</country>
76      </postal>
77      <email>jg@freedesktop.org</email>
78      <uri>http://gettys.wordpress.com/</uri>
79    </address>
80  </author>
81 
82  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
83    <organization abbrev="HP">Hewlett-Packard Company</organization>
84    <address>
85      <postal>
86        <street>HP Labs, Large Scale Systems Group</street>
87        <street>1501 Page Mill Road, MS 1177</street>
88        <city>Palo Alto</city>
89        <region>CA</region>
90        <code>94304</code>
91        <country>USA</country>
92      </postal>
93      <email>JeffMogul@acm.org</email>
94    </address>
95  </author>
96
97  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
98    <organization abbrev="Microsoft">Microsoft Corporation</organization>
99    <address>
100      <postal>
101        <street>1 Microsoft Way</street>
102        <city>Redmond</city>
103        <region>WA</region>
104        <code>98052</code>
105        <country>USA</country>
106      </postal>
107      <email>henrikn@microsoft.com</email>
108    </address>
109  </author>
110
111  <author initials="L." surname="Masinter" fullname="Larry Masinter">
112    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
113    <address>
114      <postal>
115        <street>345 Park Ave</street>
116        <city>San Jose</city>
117        <region>CA</region>
118        <code>95110</code>
119        <country>USA</country>
120      </postal>
121      <email>LMM@acm.org</email>
122      <uri>http://larry.masinter.net/</uri>
123    </address>
124  </author>
125 
126  <author initials="P." surname="Leach" fullname="Paul J. Leach">
127    <organization abbrev="Microsoft">Microsoft Corporation</organization>
128    <address>
129      <postal>
130        <street>1 Microsoft Way</street>
131        <city>Redmond</city>
132        <region>WA</region>
133        <code>98052</code>
134      </postal>
135      <email>paulle@microsoft.com</email>
136    </address>
137  </author>
138   
139  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
140    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
141    <address>
142      <postal>
143        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
144        <street>The Stata Center, Building 32</street>
145        <street>32 Vassar Street</street>
146        <city>Cambridge</city>
147        <region>MA</region>
148        <code>02139</code>
149        <country>USA</country>
150      </postal>
151      <email>timbl@w3.org</email>
152      <uri>http://www.w3.org/People/Berners-Lee/</uri>
153    </address>
154  </author>
155
156  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
157    <organization abbrev="W3C">World Wide Web Consortium</organization>
158    <address>
159      <postal>
160        <street>W3C / ERCIM</street>
161        <street>2004, rte des Lucioles</street>
162        <city>Sophia-Antipolis</city>
163        <region>AM</region>
164        <code>06902</code>
165        <country>France</country>
166      </postal>
167      <email>ylafon@w3.org</email>
168      <uri>http://www.raubacapeu.net/people/yves/</uri>
169    </address>
170  </author>
171
172  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
173    <organization abbrev="greenbytes">greenbytes GmbH</organization>
174    <address>
175      <postal>
176        <street>Hafenweg 16</street>
177        <city>Muenster</city><region>NW</region><code>48155</code>
178        <country>Germany</country>
179      </postal>
180      <phone>+49 251 2807760</phone>
181      <facsimile>+49 251 2807761</facsimile>
182      <email>julian.reschke@greenbytes.de</email>
183      <uri>http://greenbytes.de/tech/webdav/</uri>
184    </address>
185  </author>
186
187  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
188  <workgroup>HTTPbis Working Group</workgroup>
189
190<abstract>
191<t>
192   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
193   distributed, collaborative, hypertext information systems. HTTP has been in
194   use by the World Wide Web global information initiative since 1990. This
195   document is Part 4 of the seven-part specification that defines the protocol
196   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
197</t>
198<t>
199   Part 4 defines request header fields for indicating conditional requests and
200   the rules for constructing responses to those requests.
201</t>
202</abstract>
203
204<note title="Editorial Note (To be removed by RFC Editor)">
205  <t>
206    Discussion of this draft should take place on the HTTPBIS working group
207    mailing list (ietf-http-wg@w3.org), which is archived at
208    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
209  </t>
210  <t>
211    The current issues list is at
212    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
213    documents (including fancy diffs) can be found at
214    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
215  </t>
216  <t>
217    The changes in this draft are summarized in <xref target="changes.since.15"/>.
218  </t>
219</note>
220</front>
221<middle>
222<section title="Introduction" anchor="introduction">
223<t>
224   This document defines the HTTP/1.1 conditional request mechanisms,
225   including both response metadata that can be used to indicate or
226   observe changes to resource state and request header fields that
227   specify preconditions to be checked before performing the action
228   given by the request method.  Conditional GET requests are the most
229   efficient mechanism for HTTP cache updates &caching;.  Conditionals
230   can also be
231   applied to state-changing methods, such as PUT and DELETE, to prevent
232   the "lost update" problem: one client accidentally overwriting
233   the work of another client that has been acting in parallel.
234</t>
235<t>
236   Conditional request preconditions are based on the state of the target
237   resource as a whole (its current value set) or the state as observed
238   in a previously obtained representation (one value in that set).
239   A resource might have multiple current representations, each with its
240   own observable state.  The conditional request mechanisms assume that
241   the mapping of requests to corresponding representations will be
242   consistent over time if the server intends to take advantage of
243   conditionals.  Regardless, if the mapping is inconsistent and
244   the server is unable to select the appropriate representation, then
245   no harm will result when the precondition evaluates to false.
246</t>
247<t><iref primary="true" item="selected representation"/>
248   We use the term "<x:dfn>selected representation</x:dfn>" to refer to
249   the current representation of the target resource that would have been
250   selected in a successful response if the same request had used the method
251   GET and had excluded all of the conditional request header fields.
252   The conditional request preconditions are evaluated by comparing the
253   values provided in the request header fields to the current metadata
254   for the selected representation.
255</t>
256
257<section title="Requirements" anchor="intro.requirements">
258<t>
259   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
260   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
261   document are to be interpreted as described in <xref target="RFC2119"/>.
262</t>
263<t>
264   An implementation is not compliant if it fails to satisfy one or more
265   of the "MUST" or "REQUIRED" level requirements for the protocols it
266   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
267   level and all the "SHOULD" level requirements for its protocols is said
268   to be "unconditionally compliant"; one that satisfies all the "MUST"
269   level requirements but not all the "SHOULD" level requirements for its
270   protocols is said to be "conditionally compliant".
271</t>
272</section>
273
274<section title="Syntax Notation" anchor="notation">
275  <x:anchor-alias value="ALPHA"/>
276  <x:anchor-alias value="CR"/>
277  <x:anchor-alias value="DIGIT"/>
278  <x:anchor-alias value="LF"/>
279  <x:anchor-alias value="OCTET"/>
280  <x:anchor-alias value="VCHAR"/>
281  <x:anchor-alias value="WSP"/>
282  <x:anchor-alias value="core.rules"/>
283  <x:anchor-alias value="quoted-string"/>
284  <x:anchor-alias value="OWS"/>
285  <x:anchor-alias value="HTTP-date"/>
286<t>
287  This specification uses the ABNF syntax defined in &notation; (which
288  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
289  <xref target="collected.abnf"/> shows the collected ABNF, with the list
290  rule expanded.
291</t>
292<t>
293  The following core rules are included by
294  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
295  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
296  DIGIT (decimal 0-9), DQUOTE (double quote),
297  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
298  OCTET (any 8-bit sequence of data), SP (space),
299  VCHAR (any visible USASCII character),
300  and WSP (whitespace).
301</t>
302<t>
303  The ABNF rules below are defined in other parts:
304</t>
305<figure><artwork type="abnf2616">
306  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
307  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
308  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
309</artwork></figure>
310</section>
311</section>
312
313<section title="Resource State Metadata (Validators)" anchor="resource.metadata">
314   <iref primary="true" item="metadata"/>
315   <iref primary="true" item="validator"/>
316<t>
317   This specification defines two forms of metadata that are commonly used
318   to observe resource state and test for preconditions: modification dates
319   and opaque entity tags.  Additional metadata that reflects resource state
320   has been defined by various extensions of HTTP, such as WebDAV
321   <xref target="RFC4918"/>, that are beyond the scope of this specification.
322   A resource metadata value is referred to as a "<x:dfn>validator</x:dfn>"
323   when it is used within a precondition.
324</t>
325
326<section title="Last-Modified" anchor="header.last-modified">
327  <iref primary="true" item="Last-Modified header field" x:for-anchor=""/>
328  <iref primary="true" item="Header Fields" subitem="Last-Modified" x:for-anchor=""/>
329  <x:anchor-alias value="Last-Modified"/>
330<t>
331   The "Last-Modified" header field indicates the date and time at
332   which the origin server believes the selected representation was
333   last modified.
334</t>
335<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Last-Modified"/>
336  <x:ref>Last-Modified</x:ref> = <x:ref>HTTP-date</x:ref>
337</artwork></figure>
338<t>
339   An example of its use is
340</t>
341<figure><artwork type="example">
342  Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
343</artwork></figure>
344
345<section title="Generation" anchor="lastmod.generation">
346<t>
347   Origin servers &SHOULD; send Last-Modified for any selected
348   representation for which a last modification date can be reasonably
349   and consistently determined, since its use in conditional requests
350   and evaluating cache freshness (&caching;) results in a substantial
351   reduction of HTTP traffic on the Internet and can be a significant
352   factor in improving service scalability and reliability.
353</t>
354<t>
355   A representation is typically the sum of many parts behind the
356   resource interface.  The last-modified time would usually be
357   the most recent time that any of those parts were changed.
358   How that value is determined for any given resource is an
359   implementation detail beyond the scope of this specification.
360   What matters to HTTP is how recipients of the Last-Modified
361   header field can use its value to make conditional requests
362   and test the validity of locally cached responses.
363</t>
364<t>
365   An origin server &SHOULD; obtain the Last-Modified value of the
366   representation as close as possible to the time that it generates
367   the Date field-value for its response. This allows a recipient to
368   make an accurate assessment of the representation's modification time,
369   especially if the representation changes near the time that the
370   response is generated.
371</t>
372<t>
373   An origin server with a clock &MUST-NOT; send a Last-Modified date
374   that is later than the server's time of message origination (Date).
375   If the last modification time is derived from implementation-specific
376   metadata that evaluates to some time in the future, according to the
377   origin server's clock, then the origin server &MUST; replace that
378   value with the message origination date. This prevents a future
379   modification date from having an adverse impact on cache validation.
380</t>
381</section>
382
383<section title="Comparison" anchor="lastmod.comparison">
384<t>
385   A Last-Modified time, when used as a validator in a request, is
386   implicitly weak unless it is possible to deduce that it is strong,
387   using the following rules:
388  <list style="symbols">
389     <t>The validator is being compared by an origin server to the
390        actual current validator for the representation and,</t>
391     <t>That origin server reliably knows that the associated representation did
392        not change twice during the second covered by the presented
393        validator.</t>
394  </list>
395</t>
396<t>
397   or
398  <list style="symbols">
399     <t>The validator is about to be used by a client in an If-Modified-Since,
400        If-Unmodified-Since header field, because the client has a cache entry,
401        or If-Range for the associated representation, and</t>
402     <t>That cache entry includes a Date value, which gives the time
403        when the origin server sent the original response, and</t>
404     <t>The presented Last-Modified time is at least 60 seconds before
405        the Date value.</t>
406  </list>
407</t>
408<t>
409   or
410  <list style="symbols">
411     <t>The validator is being compared by an intermediate cache to the
412        validator stored in its cache entry for the representation, and</t>
413     <t>That cache entry includes a Date value, which gives the time
414        when the origin server sent the original response, and</t>
415     <t>The presented Last-Modified time is at least 60 seconds before
416        the Date value.</t>
417  </list>
418</t>
419<t>
420   This method relies on the fact that if two different responses were
421   sent by the origin server during the same second, but both had the
422   same Last-Modified time, then at least one of those responses would
423   have a Date value equal to its Last-Modified time. The arbitrary 60-second
424   limit guards against the possibility that the Date and Last-Modified
425   values are generated from different clocks, or at somewhat
426   different times during the preparation of the response. An
427   implementation &MAY; use a value larger than 60 seconds, if it is
428   believed that 60 seconds is too short.
429</t>
430</section>
431</section>
432
433<section title="ETag" anchor="header.etag">
434  <iref primary="true" item="ETag header field" x:for-anchor=""/>
435  <iref primary="true" item="Header Fields" subitem="ETag" x:for-anchor=""/>
436  <x:anchor-alias value="ETag"/>
437  <x:anchor-alias value="entity-tag"/>
438  <x:anchor-alias value="entity.tags"/>
439  <x:anchor-alias value="opaque-tag"/>
440  <x:anchor-alias value="weak"/>
441<t>
442   The ETag header field provides the current entity-tag for the
443   selected representation.
444   An entity-tag is an opaque validator for differentiating between
445   multiple representations of the same resource, regardless of whether
446   those multiple representations are due to resource state changes over
447   time, content negotiation resulting in multiple representations being
448   valid at the same time, or both. An entity-tag consists of an opaque
449   quoted string, possibly prefixed by a weakness indicator.
450</t>
451<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"/>
452  <x:ref>ETag</x:ref>       = <x:ref>entity-tag</x:ref>
453
454  <x:ref>entity-tag</x:ref> = [ <x:ref>weak</x:ref> ] <x:ref>opaque-tag</x:ref>
455  <x:ref>weak</x:ref>       = <x:abnf-char-sequence>"W/"</x:abnf-char-sequence> ; "W/", case-sensitive
456  <x:ref>opaque-tag</x:ref> = <x:ref>quoted-string</x:ref>
457</artwork></figure>
458<t>
459   An entity-tag can be more reliable for validation than a modification
460   date in situations where it is inconvenient to store modification
461   dates, where the one-second resolution of HTTP date values is not
462   sufficient, or where modification dates are not consistently maintained.
463</t>
464<figure><preamble>
465  Examples:
466</preamble>
467<artwork type="example">
468  ETag: "xyzzy"
469  ETag: W/"xyzzy"
470  ETag: ""
471</artwork></figure>
472
473<section title="Generation" anchor="entity.tag.generation">
474<t>
475   The principle behind entity-tags is that only the service author
476   knows the implementation of a resource well enough to select the
477   most accurate and efficient validation mechanism for that resource,
478   and that any such mechanism can be mapped to a simple sequence of
479   octets for easy comparison.  Since the value is opaque, there is no
480   need for the client to be aware of how each entity-tag is constructed.
481</t>
482<t>
483   For example, a resource that has implementation-specific versioning
484   applied to all changes might use an internal revision number, perhaps
485   combined with a variance identifier for content negotiation, to
486   accurately differentiate between representations.
487   Other implementations might use a stored hash of representation content,
488   a combination of various filesystem attributes, or a modification
489   timestamp that has sub-second resolution.
490</t>
491<t>
492   Origin servers &SHOULD; send ETag for any selected representation
493   for which detection of changes can be reasonably and consistently
494   determined, since the entity-tag's use in conditional requests and
495   evaluating cache freshness (&caching;) can result in a substantial
496   reduction of HTTP network traffic and can be a significant factor in
497   improving service scalability and reliability.
498</t>
499</section>
500
501<section title="Weak versus Strong" anchor="weak.and.strong.validators">
502<t>
503   Since both origin servers and caches will compare two validators to
504   decide if they indicate the same or different representations, one
505   normally would expect that if the representation (including both
506   representation header fields and representation body) changes in any
507   way, then the associated validator would change as well. If this is
508   true, then we call that validator a "strong validator".  One example
509   of a strong validator is an integer that is incremented in stable
510   storage every time a representation is changed.
511</t>
512<t>
513   However, there might be cases when a server prefers to change the
514   validator only when it desires cached representations to be invalidated.
515   For example, the representation of a weather report that changes in
516   content every second, based on dynamic measurements, might be grouped
517   into sets of equivalent representations (from the origin server's
518   perspective) in order to allow cached representations to be valid
519   for a reasonable period of time (perhaps adjusted dynamically based
520   on server load or weather quality).
521   A validator that does not always change when the representation
522   changes is a "weak validator".
523</t>
524<t>
525   One can think of a strong validator as part of an identifier for a
526   specific representation, whereas a weak validator is part of an
527   identifier for a set of equivalent representations (where this notion
528   of equivalence is entirely governed by the origin server and beyond
529   the scope of this specification).
530</t>
531<t>
532   An entity-tag is normally a strong validator, but the protocol
533   provides a mechanism to tag an entity-tag as "weak".
534  <list><t>
535      A representation's modification time, if defined with only one-second
536      resolution, could be a weak validator, since it is possible that
537      the representation might be modified twice during a single second.
538    </t><t>
539      Support for weak validators is optional. However, weak validators
540      allow for more efficient caching of equivalent objects; for
541      example, a hit counter on a site is probably good enough if it is
542      updated every few days or weeks, and any value during that period
543      is likely "good enough" to be equivalent.
544    </t></list>
545</t>
546<t>
547   A strong entity-tag &MUST; change whenever the associated representation
548   changes in any way. A weak entity-tag &SHOULD; change whenever the origin
549   server considers prior representations to be unacceptable as a substitute
550   for the current representation. In other words, a weak entity tag &SHOULD;
551   change whenever the origin server wants caches to invalidate old responses.
552</t>
553<t>
554   A "strong entity-tag" &MAY; be shared by two representations of a resource
555   only if they are equivalent by octet equality.
556</t>
557<t>
558   A "weak entity-tag", indicated by the "W/" prefix, &MAY; be shared by
559   two representations of a resource. A weak entity-tag can only be used
560   for weak comparison.
561</t>
562<t>
563   Cache entries might persist for arbitrarily long periods, regardless
564   of expiration times.  Thus, a cache might attempt to validate an
565   entry using a validator that it obtained in the distant past.
566   A strong entity-tag &MUST; be unique across all versions of all
567   representations associated with a particular resource over time.
568   However, there is no implication of uniqueness across entity-tags
569   of different resources (i.e., the same entity-tag value might be
570   in use for representations of multiple resources at the same time
571   and does not imply that those representations are equivalent).
572</t>
573</section>
574
575<section title="Comparison" anchor="entity.tag.comparison">
576  <x:anchor-alias value="validator.comparison"/>
577<t>
578   There are two entity-tag comparison functions, depending
579   on whether the comparison context allows the use of weak validators
580   or not:
581  <list style="symbols">
582     <t>The strong comparison function: in order to be considered equal,
583        both opaque-tags &MUST; be identical character-by-character, and both
584        &MUST-NOT; be weak.</t>
585     <t>The weak comparison function: in order to be considered equal, both
586        opaque-tags &MUST; be identical character-by-character, but
587        either or both of them &MAY; be tagged as "weak" without affecting
588        the result.</t>
589  </list>
590</t>
591<t>
592   A "use" of a validator is either when a client generates a request
593   and includes the validator in a precondition, or when a server
594   compares two validators.
595</t>
596<t>
597   Strong validators are usable in any context. Weak validators are only
598   usable in contexts that do not depend on exact equality of a representation.
599   For example, either kind is usable for a normal conditional GET.
600</t>
601<t>
602   The example below shows the results for a set of entity-tag pairs,
603   and both the weak and strong comparison function results:
604</t>
605<texttable align="left">
606  <ttcol>ETag 1</ttcol>
607  <ttcol>ETag 2</ttcol>
608  <ttcol>Strong Comparison</ttcol>
609  <ttcol>Weak Comparison</ttcol>
610
611  <c>W/"1"</c>
612  <c>W/"1"</c>
613  <c>no match</c>
614  <c>match</c>
615 
616  <c>W/"1"</c>
617  <c>W/"2"</c>
618  <c>no match</c>
619  <c>no match</c>
620
621  <c>W/"1"</c>
622  <c>"1"</c>
623  <c>no match</c>
624  <c>match</c>
625
626  <c>"1"</c>
627  <c>"1"</c>
628  <c>match</c>
629  <c>match</c>
630</texttable>
631<t>
632   An entity-tag is strong unless it is explicitly tagged as weak.
633</t>
634</section>
635
636<section title="Rules for When to Use Entity-tags and Last-Modified Dates" anchor="rules.for.when.to.use.entity.tags.and.last-modified.dates">
637<t>
638   We adopt a set of rules and recommendations for origin servers,
639   clients, and caches regarding when various validator types ought to
640   be used, and for what purposes.
641</t>
642<t>
643   HTTP/1.1 origin servers:
644  <list style="symbols">
645     <t>&SHOULD; send an entity-tag validator unless it is not feasible to
646        generate one.</t>
647
648     <t>&MAY; send a weak entity-tag instead of a strong entity-tag, if
649        performance considerations support the use of weak entity-tags,
650        or if it is unfeasible to send a strong entity-tag.</t>
651
652     <t>&SHOULD; send a Last-Modified value if it is feasible to send one.</t>
653  </list>
654</t>
655<t>
656   In other words, the preferred behavior for an HTTP/1.1 origin server
657   is to send both a strong entity-tag and a Last-Modified value.
658</t>
659<t>
660   HTTP/1.1 clients:
661  <list style="symbols">
662     <t>&MUST; use that entity-tag in any cache-conditional request (using
663        If-Match or If-None-Match) if an entity-tag has been provided by the
664        origin server.</t>
665
666     <t>&SHOULD; use the Last-Modified value in non-subrange cache-conditional
667        requests (using If-Modified-Since) if only a Last-Modified value has
668        been provided by the origin server. </t>
669
670     <t>&MAY; use the Last-Modified value in subrange cache-conditional
671        requests (using If-Unmodified-Since) if only a Last-Modified value has
672        been provided by an HTTP/1.0 origin server. The user agent &SHOULD;
673        provide a way to disable this, in case of difficulty.</t>
674
675     <t>&SHOULD; use both validators in cache-conditional requests if both an
676        entity-tag and a Last-Modified value have been provided by the origin
677        server. This allows both HTTP/1.0 and HTTP/1.1 caches to respond
678        appropriately.</t>
679  </list>
680</t>
681<t>
682   An HTTP/1.1 origin server, upon receiving a conditional request that
683   includes both a Last-Modified date (e.g., in an If-Modified-Since or
684   If-Unmodified-Since header field) and one or more entity-tags (e.g.,
685   in an If-Match, If-None-Match, or If-Range header field) as cache
686   validators, &MUST-NOT; return a response status code of 304 (Not Modified)
687   unless doing so is consistent with all of the conditional header
688   fields in the request.
689</t>
690<t>
691   An HTTP/1.1 caching proxy, upon receiving a conditional request that
692   includes both a Last-Modified date and one or more entity-tags as
693   cache validators, &MUST-NOT; return a locally cached response to the
694   client unless that cached response is consistent with all of the
695   conditional header fields in the request.
696  <list><t>
697      <x:h>Note:</x:h> The general principle behind these rules is that HTTP/1.1
698      servers and clients ought to transmit as much non-redundant
699      information as is available in their responses and requests.
700      HTTP/1.1 systems receiving this information will make the most
701      conservative assumptions about the validators they receive.
702  </t><t>
703      HTTP/1.0 clients and caches might ignore entity-tags. Generally,
704      last-modified values received or used by these systems will
705      support transparent and efficient caching, and so HTTP/1.1 origin
706      servers should provide Last-Modified values. In those rare cases
707      where the use of a Last-Modified value as a validator by an
708      HTTP/1.0 system could result in a serious problem, then HTTP/1.1
709      origin servers should not provide one.
710  </t></list>
711</t>
712</section>
713
714<section title="Example: Entity-tags varying on Content-Negotiated Resources" anchor="example.entity.tag.vs.conneg">
715<t>
716   Consider a resource that is subject to content negotiation (&content-negotiation;),
717   and where the representations returned upon a GET request vary based on
718   the Accept-Encoding request header field (&header-accept-encoding;):
719</t>
720<figure><preamble>>> Request:</preamble><artwork type="message/http; msgtype=&#34;request&#34;"  x:indent-with="  ">
721GET /index HTTP/1.1
722Host: www.example.com
723Accept-Encoding: gzip
724
725</artwork></figure>
726<t>
727   In this case, the response might or might not use the gzip content coding.
728   If it does not, the response might look like:
729</t>
730<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
731HTTP/1.1 200 OK
732Date: Thu, 26 Mar 2010 00:05:00 GMT
733ETag: "123-a"
734Content-Length: <x:length-of target="exbody"/>
735Vary: Accept-Encoding
736Content-Type: text/plain
737
738<x:span anchor="exbody">Hello World!
739Hello World!
740Hello World!
741Hello World!
742Hello World!
743</x:span></artwork></figure>
744<t>
745   An alternative representation that does use gzip content coding would be:
746</t>
747<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
748HTTP/1.1 200 OK
749Date: Thu, 26 Mar 2010 00:05:00 GMT
750ETag: "123-b"
751Content-Length: 43
752Vary: Accept-Encoding
753Content-Type: text/plain
754Content-Encoding: gzip
755
756<spanx>...binary data...</spanx></artwork></figure>
757<x:note>
758  <t>
759    <x:h>Note:</x:h> Content codings are a property of the representation,
760    so therefore an entity-tag of an encoded representation must be distinct
761    from an unencoded representation to prevent conflicts during cache updates
762    and range requests.  In contrast, transfer codings (&transfer-codings;)
763    apply only during message transfer and do not require distinct entity-tags.
764  </t>
765</x:note>
766</section>
767</section>
768</section>
769
770<section title="Precondition Header Fields" anchor="header.fields">
771<t>
772   This section defines the syntax and semantics of HTTP/1.1 header fields
773   for applying preconditions on requests.
774</t>
775
776<section title="If-Match" anchor="header.if-match">
777  <iref primary="true" item="If-Match header field" x:for-anchor=""/>
778  <iref primary="true" item="Header Fields" subitem="If-Match" x:for-anchor=""/>
779  <x:anchor-alias value="If-Match"/>
780<t>
781   The "If-Match" header field &MAY; be used to make a request method
782   conditional on the current existence or value of an entity-tag for
783   one or more representations of the target resource.  If-Match is
784   generally useful for resource update requests, such as PUT requests,
785   as a means for protecting against accidental overwrites when multiple
786   clients are acting in parallel on the same resource (i.e., the
787   "lost update" problem).  An If-Match field-value of "*" places the
788   precondition on the existence of any current representation for the
789   target resource.
790</t>
791<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Match"/>
792  <x:ref>If-Match</x:ref> = "*" / 1#<x:ref>entity-tag</x:ref>
793</artwork></figure>
794<t>
795   If any of the entity-tags listed in the If-Match field value match
796   (as per <xref target="entity.tag.comparison"/>) the entity-tag of the
797   selected representation for the target resource,
798   or if "*" is given and any current representation exists for the
799   target resource, then the server &MAY; perform the request method
800   as if the If-Match header field was not present.
801</t>
802<t>
803   If none of the entity-tags match, or if "*" is given and no current
804   representation exists, the server &MUST-NOT; perform the requested method.
805   Instead, the server &MUST; respond with the 412 (Precondition Failed)
806   status code.
807</t>
808<t>
809   If the request would, without the If-Match header field, result in
810   anything other than a 2xx or 412 status code, then the If-Match header field
811   &MUST; be ignored.
812</t>
813<t>
814   Examples:
815</t>
816<figure><artwork type="example">
817  If-Match: "xyzzy"
818  If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
819  If-Match: *
820</artwork></figure>
821<t>
822   The result of a request having both an If-Match header field and
823   either an If-None-Match or an If-Modified-Since header fields is
824   undefined by this specification.
825</t>
826</section>
827
828<section title="If-None-Match" anchor="header.if-none-match">
829  <iref primary="true" item="If-None-Match header field" x:for-anchor=""/>
830  <iref primary="true" item="Header Fields" subitem="If-None-Match" x:for-anchor=""/>
831  <x:anchor-alias value="If-None-Match"/>
832<t>
833   The "If-None-Match" header field &MAY; be used to make a request method
834   conditional on not matching any of the current entity-tag values for
835   representations of the target resource.  If-None-Match is primarily
836   used in conditional GET requests to enable efficient updates of cached
837   information with a minimum amount of transaction overhead.  A client
838   that has one or more representations previously obtained from the
839   target resource can send If-None-Match with a list of the associated
840   entity-tags in the hope of receiving a 304 response if at least one
841   of those representations matches the selected representation.
842</t>
843<t>
844   If-None-Match MAY also be used with a value of "*" to prevent an unsafe
845   request method (e.g., PUT) from inadvertently modifying an existing
846   representation of the target resource when the client believes that
847   the resource does not have a current representation.  This is a variation
848   on the "lost update" problem that might arise if more than one client
849   attempts to create an initial representation for the target resource.
850</t>
851<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-None-Match"/>
852  <x:ref>If-None-Match</x:ref> = "*" / 1#<x:ref>entity-tag</x:ref>
853</artwork></figure>
854<t>
855   If any of the entity-tags listed in the If-None-Match field-value match
856   (as per <xref target="entity.tag.comparison"/>) the entity-tag of the
857   selected representation, or if "*" is
858   given and any current representation exists for that resource, then the
859   server &MUST-NOT; perform the requested method.
860   Instead, if the request method was GET or HEAD, the server &SHOULD;
861   respond with a 304 (Not Modified) status code, including the cache-related
862   header fields (particularly ETag) of the selected representation that has
863   a matching entity-tag.  For all other request methods, the server &MUST;
864   respond with a 412 (Precondition Failed) status code.
865</t>
866<t>
867   If none of the entity-tags match, then the server &MAY; perform the
868   requested method as if the If-None-Match header field did not exist,
869   but &MUST; also ignore any If-Modified-Since header field(s) in the
870   request. That is, if no entity-tags match, then the server &MUST-NOT;
871   return a 304 (Not Modified) response.
872</t>
873<t>
874   If the request would, without the If-None-Match header field, result
875   in anything other than a 2xx or 304 status code, then the If-None-Match
876   header field &MUST; be ignored. (See <xref
877   target="rules.for.when.to.use.entity.tags.and.last-modified.dates"/> for
878   a discussion of server behavior when both If-Modified-Since and
879   If-None-Match appear in the same request.)
880</t>
881<t>
882   Examples:
883</t>
884<figure><artwork type="example">
885  If-None-Match: "xyzzy"
886  If-None-Match: W/"xyzzy"
887  If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
888  If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
889  If-None-Match: *
890</artwork></figure>
891<t>
892   The result of a request having both an If-None-Match header field and
893   either an If-Match or an If-Unmodified-Since header fields is
894   undefined by this specification.
895</t>
896</section>
897
898<section title="If-Modified-Since" anchor="header.if-modified-since">
899  <iref primary="true" item="If-Modified-Since header field" x:for-anchor=""/>
900  <iref primary="true" item="Header Fields" subitem="If-Modified-Since" x:for-anchor=""/>
901  <x:anchor-alias value="If-Modified-Since"/>
902<t>
903   The "If-Modified-Since" header field &MAY; be used to make a request
904   method conditional by modification date: if the selected representation
905   has not been modified since the time specified in this field, then
906   do not perform the request method; instead, respond as detailed below.
907</t>
908<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Modified-Since"/>
909  <x:ref>If-Modified-Since</x:ref> = <x:ref>HTTP-date</x:ref>
910</artwork></figure>
911<t>
912   An example of the field is:
913</t>
914<figure><artwork type="example">
915  If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
916</artwork></figure>
917<t>
918   A GET method with an If-Modified-Since header field and no Range header
919   field requests that the selected representation be transferred only if
920   it has been modified since the date given by the If-Modified-Since
921   header field.
922   The algorithm for determining this includes the following cases:
923  <list style="numbers">
924      <t>If the request would normally result in anything other than a
925         200 (OK) status code, or if the passed If-Modified-Since date is
926         invalid, the response is exactly the same as for a normal GET.
927         A date which is later than the server's current time is
928         invalid.</t>
929
930      <t>If the selected representation has been modified since the
931         If-Modified-Since date, the response is exactly the same as for
932         a normal GET.</t>
933
934      <t>If the selected representation has not been modified since a valid
935         If-Modified-Since date, the server &SHOULD; return a
936         304 (Not Modified) response.</t>
937  </list>
938</t>
939<t>
940   The purpose of this feature is to allow efficient updates of cached
941   information with a minimum amount of transaction overhead.
942  <list><t>
943      <x:h>Note:</x:h> The Range header field modifies the meaning of If-Modified-Since;
944      see &header-range; for full details.
945    </t><t>
946      <x:h>Note:</x:h> If-Modified-Since times are interpreted by the server, whose
947      clock might not be synchronized with the client.
948    </t><t>
949      <x:h>Note:</x:h> When handling an If-Modified-Since header field, some
950      servers will use an exact date comparison function, rather than a
951      less-than function, for deciding whether to send a 304 (Not
952      Modified) response. To get best results when sending an If-Modified-Since
953      header field for cache validation, clients are
954      advised to use the exact date string received in a previous Last-Modified
955      header field whenever possible.
956    </t><t>
957      <x:h>Note:</x:h> If a client uses an arbitrary date in the If-Modified-Since
958      header field instead of a date taken from the Last-Modified header field for
959      the same request, the client needs to be aware that this
960      date is interpreted in the server's understanding of time.
961      Unsynchronized clocks and rounding problems, due to the different
962      encodings of time between the client and server, are concerns.
963      This includes the possibility of race conditions if the
964      document has changed between the time it was first requested and
965      the If-Modified-Since date of a subsequent request, and the
966      possibility of clock-skew-related problems if the If-Modified-Since
967      date is derived from the client's clock without correction
968      to the server's clock. Corrections for different time bases
969      between client and server are at best approximate due to network
970      latency.
971    </t>
972  </list>
973</t>
974<t>
975   The result of a request having both an If-Modified-Since header field
976   and either an If-Match or an If-Unmodified-Since header fields is
977   undefined by this specification.
978</t>
979</section>
980
981<section title="If-Unmodified-Since" anchor="header.if-unmodified-since">
982  <iref primary="true" item="If-Unmodified-Since header field" x:for-anchor=""/>
983  <iref primary="true" item="Header Fields" subitem="If-Unmodified-Since" x:for-anchor=""/>
984  <x:anchor-alias value="If-Unmodified-Since"/>
985<t>
986   The "If-Unmodified-Since" header field &MAY; be used to make a request
987   method conditional by modification date: if the selected representation
988   has been modified since the time specified in this field, then the
989   server &MUST-NOT; perform the requested operation and &MUST; instead
990   respond with the 412 (Precondition Failed) status code.
991   If the selected representation has not been modified since the time
992   specified in this field, the server &SHOULD; perform the request
993   method as if the If-Unmodified-Since header field were not present.
994</t>
995<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Unmodified-Since"/>
996  <x:ref>If-Unmodified-Since</x:ref> = <x:ref>HTTP-date</x:ref>
997</artwork></figure>
998<t>
999   An example of the field is:
1000</t>
1001<figure><artwork type="example">
1002  If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
1003</artwork></figure>
1004<t>
1005   If the request normally (i.e., without the If-Unmodified-Since
1006   header field) would result in anything other than a 2xx or 412 status code,
1007   the If-Unmodified-Since header field &SHOULD; be ignored.
1008</t>
1009<t>
1010   If the specified date is invalid, the header field &MUST; be ignored.
1011</t>
1012<t>
1013   The result of a request having both an If-Unmodified-Since header
1014   field and either an If-None-Match or an If-Modified-Since header
1015   fields is undefined by this specification.
1016</t>
1017</section>
1018
1019<section title="If-Range" anchor="header.if-range">
1020<t>
1021   The If-Range header field provides a special conditional request
1022   mechanism that is similar to If-Match and If-Unmodified-Since but
1023   specific to HTTP range requests. If-Range is defined in &header-if-range;.
1024</t>
1025</section>
1026
1027</section>
1028
1029<section title="Status Code Definitions" anchor="status.code.definitions">
1030<section title="304 Not Modified" anchor="status.304">
1031  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1032  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1033<t>
1034   The 304 status code indicates that a conditional GET request has been
1035   received and would have resulted in a 200 (OK) response if it were not
1036   for the fact that the condition has evaluated to false.  In other words,
1037   there is no need for the server to transfer a representation of the
1038   target resource because the client's request indicates that it already
1039   has a valid representation, as indicated by the 304 response header
1040   fields, and is therefore redirecting the client to make use of that
1041   stored representation as if it were the payload of a 200 response.
1042   The 304 response &MUST-NOT; contain a message-body, and thus is always
1043   terminated by the first empty line after the header fields.
1044</t>
1045<t>
1046   A 304 response &MUST; include a Date header field (&header-date;)
1047   unless its omission is required by &clockless;.  If a 200 response
1048   to the same request would have included any of the header fields
1049   Cache-Control, Content-Location, ETag, Expires, Last-Modified, or
1050   Vary, then those same header fields &MUST; be sent in a 304 response.
1051</t>
1052<t>
1053   Since the goal of a 304 response is to minimize information transfer
1054   when the recipient already has one or more cached representations,
1055   the response &SHOULD-NOT; include representation metadata other
1056   than the above listed fields unless said metadata exists for the
1057   purpose of guiding cache updates (e.g., future HTTP extensions).
1058</t>
1059<t>
1060   If the recipient of a 304 response does not have a cached representation
1061   corresponding to the entity-tag indicated by the 304 response, then the
1062   recipient &MUST-NOT; use the 304 to update its own cache.  If this
1063   conditional request originated with an outbound client, such as a
1064   user agent with its own cache sending a conditional GET to a shared
1065   proxy, then the 304 response &MAY; be forwarded to the outbound client.
1066   Otherwise, the recipient &MUST; disregard the 304 response and repeat
1067   the request without any preconditions.
1068</t>
1069<t>
1070   If a cache uses a received 304 response to update a cache entry, the
1071   cache &MUST; update the entry to reflect any new field values given in
1072   the response.
1073</t>
1074</section>
1075
1076<section title="412 Precondition Failed" anchor="status.412">
1077  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1078  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1079<t>
1080   The 412 status code indicates that one or more preconditions given in
1081   the request header fields evaluated to false when tested on the server.
1082   This response code allows the client to place preconditions on the
1083   current resource state (its current representations and metadata)
1084   and thus prevent the request method from being applied if the target
1085   resource is in an unexpected state.
1086</t>
1087</section>
1088</section>
1089
1090<section title="IANA Considerations" anchor="IANA.considerations">
1091
1092<section title="Status Code Registration" anchor="status.code.registration">
1093<t>
1094   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
1095   shall be updated with the registrations below:
1096</t>
1097<?BEGININC p4-conditional.iana-status-codes ?>
1098<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
1099<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
1100   <ttcol>Value</ttcol>
1101   <ttcol>Description</ttcol>
1102   <ttcol>Reference</ttcol>
1103   <c>304</c>
1104   <c>Not Modified</c>
1105   <c>
1106      <xref target="status.304"/>
1107   </c>
1108   <c>412</c>
1109   <c>Precondition Failed</c>
1110   <c>
1111      <xref target="status.412"/>
1112   </c>
1113</texttable>
1114<!--(END)-->
1115<?ENDINC p4-conditional.iana-status-codes ?>
1116</section>
1117
1118<section title="Header Field Registration" anchor="header.field.registration">
1119<t>
1120   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1121   with the permanent registrations below (see <xref target="RFC3864"/>):
1122</t>
1123<?BEGININC p4-conditional.iana-headers ?>
1124<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1125<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1126   <ttcol>Header Field Name</ttcol>
1127   <ttcol>Protocol</ttcol>
1128   <ttcol>Status</ttcol>
1129   <ttcol>Reference</ttcol>
1130
1131   <c>ETag</c>
1132   <c>http</c>
1133   <c>standard</c>
1134   <c>
1135      <xref target="header.etag"/>
1136   </c>
1137   <c>If-Match</c>
1138   <c>http</c>
1139   <c>standard</c>
1140   <c>
1141      <xref target="header.if-match"/>
1142   </c>
1143   <c>If-Modified-Since</c>
1144   <c>http</c>
1145   <c>standard</c>
1146   <c>
1147      <xref target="header.if-modified-since"/>
1148   </c>
1149   <c>If-None-Match</c>
1150   <c>http</c>
1151   <c>standard</c>
1152   <c>
1153      <xref target="header.if-none-match"/>
1154   </c>
1155   <c>If-Unmodified-Since</c>
1156   <c>http</c>
1157   <c>standard</c>
1158   <c>
1159      <xref target="header.if-unmodified-since"/>
1160   </c>
1161   <c>Last-Modified</c>
1162   <c>http</c>
1163   <c>standard</c>
1164   <c>
1165      <xref target="header.last-modified"/>
1166   </c>
1167</texttable>
1168<!--(END)-->
1169<?ENDINC p4-conditional.iana-headers ?>
1170<t>
1171   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1172</t>
1173</section>
1174</section>
1175
1176<section title="Security Considerations" anchor="security.considerations">
1177<t>
1178   No additional security considerations have been identified beyond
1179   those applicable to HTTP in general &messaging;.
1180</t>
1181</section>
1182
1183<section title="Acknowledgments" anchor="acks">
1184<t>
1185  See &acks;.
1186</t>
1187</section>
1188</middle>
1189<back>
1190
1191<references title="Normative References">
1192
1193<reference anchor="Part1">
1194  <front>
1195    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1196    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1197      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1198      <address><email>fielding@gbiv.com</email></address>
1199    </author>
1200    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1201      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1202      <address><email>jg@freedesktop.org</email></address>
1203    </author>
1204    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1205      <organization abbrev="HP">Hewlett-Packard Company</organization>
1206      <address><email>JeffMogul@acm.org</email></address>
1207    </author>
1208    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1209      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1210      <address><email>henrikn@microsoft.com</email></address>
1211    </author>
1212    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1213      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1214      <address><email>LMM@acm.org</email></address>
1215    </author>
1216    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1217      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1218      <address><email>paulle@microsoft.com</email></address>
1219    </author>
1220    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1221      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1222      <address><email>timbl@w3.org</email></address>
1223    </author>
1224    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1225      <organization abbrev="W3C">World Wide Web Consortium</organization>
1226      <address><email>ylafon@w3.org</email></address>
1227    </author>
1228    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1229      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1230      <address><email>julian.reschke@greenbytes.de</email></address>
1231    </author>
1232    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1233  </front>
1234  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1235  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1236</reference>
1237
1238<reference anchor="Part3">
1239  <front>
1240    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
1241    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1242      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1243      <address><email>fielding@gbiv.com</email></address>
1244    </author>
1245    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1246      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1247      <address><email>jg@freedesktop.org</email></address>
1248    </author>
1249    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1250      <organization abbrev="HP">Hewlett-Packard Company</organization>
1251      <address><email>JeffMogul@acm.org</email></address>
1252    </author>
1253    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1254      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1255      <address><email>henrikn@microsoft.com</email></address>
1256    </author>
1257    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1258      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1259      <address><email>LMM@acm.org</email></address>
1260    </author>
1261    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1262      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1263      <address><email>paulle@microsoft.com</email></address>
1264    </author>
1265    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1266      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1267      <address><email>timbl@w3.org</email></address>
1268    </author>
1269    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1270      <organization abbrev="W3C">World Wide Web Consortium</organization>
1271      <address><email>ylafon@w3.org</email></address>
1272    </author>
1273    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1274      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1275      <address><email>julian.reschke@greenbytes.de</email></address>
1276    </author>
1277    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1278  </front>
1279  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
1280  <x:source href="p3-payload.xml" basename="p3-payload"/>
1281</reference>
1282
1283<reference anchor="Part5">
1284  <front>
1285    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1286    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1287      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1288      <address><email>fielding@gbiv.com</email></address>
1289    </author>
1290    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1291      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1292      <address><email>jg@freedesktop.org</email></address>
1293    </author>
1294    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1295      <organization abbrev="HP">Hewlett-Packard Company</organization>
1296      <address><email>JeffMogul@acm.org</email></address>
1297    </author>
1298    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1299      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1300      <address><email>henrikn@microsoft.com</email></address>
1301    </author>
1302    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1303      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1304      <address><email>LMM@acm.org</email></address>
1305    </author>
1306    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1307      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1308      <address><email>paulle@microsoft.com</email></address>
1309    </author>
1310    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1311      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1312      <address><email>timbl@w3.org</email></address>
1313    </author>
1314    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1315      <organization abbrev="W3C">World Wide Web Consortium</organization>
1316      <address><email>ylafon@w3.org</email></address>
1317    </author>
1318    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1319      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1320      <address><email>julian.reschke@greenbytes.de</email></address>
1321    </author>
1322    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1323  </front>
1324  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1325  <x:source href="p5-range.xml" basename="p5-range"/>
1326</reference>
1327
1328<reference anchor="Part6">
1329  <front>
1330    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1331    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1332      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1333      <address><email>fielding@gbiv.com</email></address>
1334    </author>
1335    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1336      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1337      <address><email>jg@freedesktop.org</email></address>
1338    </author>
1339    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1340      <organization abbrev="HP">Hewlett-Packard Company</organization>
1341      <address><email>JeffMogul@acm.org</email></address>
1342    </author>
1343    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1344      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1345      <address><email>henrikn@microsoft.com</email></address>
1346    </author>
1347    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1348      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1349      <address><email>LMM@acm.org</email></address>
1350    </author>
1351    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1352      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1353      <address><email>paulle@microsoft.com</email></address>
1354    </author>
1355    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1356      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1357      <address><email>timbl@w3.org</email></address>
1358    </author>
1359    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1360      <organization abbrev="W3C">World Wide Web Consortium</organization>
1361      <address><email>ylafon@w3.org</email></address>
1362    </author>
1363    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1364      <address><email>mnot@mnot.net</email></address>
1365    </author>
1366    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1367      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1368      <address><email>julian.reschke@greenbytes.de</email></address>
1369    </author>
1370    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1371  </front>
1372  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1373  <x:source href="p6-cache.xml" basename="p6-cache"/>
1374</reference>
1375
1376<reference anchor="RFC2119">
1377  <front>
1378    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1379    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1380      <organization>Harvard University</organization>
1381      <address><email>sob@harvard.edu</email></address>
1382    </author>
1383    <date month="March" year="1997"/>
1384  </front>
1385  <seriesInfo name="BCP" value="14"/>
1386  <seriesInfo name="RFC" value="2119"/>
1387</reference>
1388
1389<reference anchor="RFC5234">
1390  <front>
1391    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1392    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1393      <organization>Brandenburg InternetWorking</organization>
1394      <address>
1395        <email>dcrocker@bbiw.net</email>
1396      </address> 
1397    </author>
1398    <author initials="P." surname="Overell" fullname="Paul Overell">
1399      <organization>THUS plc.</organization>
1400      <address>
1401        <email>paul.overell@thus.net</email>
1402      </address>
1403    </author>
1404    <date month="January" year="2008"/>
1405  </front>
1406  <seriesInfo name="STD" value="68"/>
1407  <seriesInfo name="RFC" value="5234"/>
1408</reference>
1409
1410</references>
1411
1412<references title="Informative References">
1413
1414<reference anchor="RFC2616">
1415  <front>
1416    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1417    <author initials="R." surname="Fielding" fullname="R. Fielding">
1418      <organization>University of California, Irvine</organization>
1419      <address><email>fielding@ics.uci.edu</email></address>
1420    </author>
1421    <author initials="J." surname="Gettys" fullname="J. Gettys">
1422      <organization>W3C</organization>
1423      <address><email>jg@w3.org</email></address>
1424    </author>
1425    <author initials="J." surname="Mogul" fullname="J. Mogul">
1426      <organization>Compaq Computer Corporation</organization>
1427      <address><email>mogul@wrl.dec.com</email></address>
1428    </author>
1429    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1430      <organization>MIT Laboratory for Computer Science</organization>
1431      <address><email>frystyk@w3.org</email></address>
1432    </author>
1433    <author initials="L." surname="Masinter" fullname="L. Masinter">
1434      <organization>Xerox Corporation</organization>
1435      <address><email>masinter@parc.xerox.com</email></address>
1436    </author>
1437    <author initials="P." surname="Leach" fullname="P. Leach">
1438      <organization>Microsoft Corporation</organization>
1439      <address><email>paulle@microsoft.com</email></address>
1440    </author>
1441    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1442      <organization>W3C</organization>
1443      <address><email>timbl@w3.org</email></address>
1444    </author>
1445    <date month="June" year="1999"/>
1446  </front>
1447  <seriesInfo name="RFC" value="2616"/>
1448</reference>
1449
1450<reference anchor='RFC3864'>
1451  <front>
1452    <title>Registration Procedures for Message Header Fields</title>
1453    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
1454      <organization>Nine by Nine</organization>
1455      <address><email>GK-IETF@ninebynine.org</email></address>
1456    </author>
1457    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
1458      <organization>BEA Systems</organization>
1459      <address><email>mnot@pobox.com</email></address>
1460    </author>
1461    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
1462      <organization>HP Labs</organization>
1463      <address><email>JeffMogul@acm.org</email></address>
1464    </author>
1465    <date year='2004' month='September' />
1466  </front>
1467  <seriesInfo name='BCP' value='90' />
1468  <seriesInfo name='RFC' value='3864' />
1469</reference>
1470
1471<reference anchor='RFC4918'>
1472  <front>
1473    <title>HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)</title>
1474    <author initials="L.M." surname="Dusseault" fullname="Lisa Dusseault" role="editor" >
1475      <organization abbrev="CommerceNet">CommerceNet</organization>
1476      <address><email>ldusseault@commerce.net</email></address>
1477    </author>
1478    <date month="June" year="2007" />
1479  </front>
1480  <seriesInfo name='RFC' value='4918' />
1481</reference>
1482</references>
1483
1484<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
1485<t>
1486  Allow weak entity-tags in all requests except range requests (Sections
1487  <xref target="weak.and.strong.validators" format="counter"/> and
1488  <xref target="header.if-none-match" format="counter"/>).
1489</t>
1490<t>
1491  Change ABNF productions for header fields to only define the field value.
1492  (<xref target="header.fields"/>)
1493</t>
1494</section>
1495
1496<?BEGININC p4-conditional.abnf-appendix ?>
1497<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
1498<figure>
1499<artwork type="abnf" name="p4-conditional.parsed-abnf">
1500<x:ref>ETag</x:ref> = entity-tag
1501
1502<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
1503
1504<x:ref>If-Match</x:ref> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
1505 entity-tag ] ) )
1506<x:ref>If-Modified-Since</x:ref> = HTTP-date
1507<x:ref>If-None-Match</x:ref> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
1508 entity-tag ] ) )
1509<x:ref>If-Unmodified-Since</x:ref> = HTTP-date
1510
1511<x:ref>Last-Modified</x:ref> = HTTP-date
1512
1513<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
1514
1515<x:ref>entity-tag</x:ref> = [ weak ] opaque-tag
1516
1517<x:ref>opaque-tag</x:ref> = quoted-string
1518
1519<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
1520
1521<x:ref>weak</x:ref> = %x57.2F ; W/
1522</artwork>
1523</figure>
1524<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
1525; ETag defined but not used
1526; If-Match defined but not used
1527; If-Modified-Since defined but not used
1528; If-None-Match defined but not used
1529; If-Unmodified-Since defined but not used
1530; Last-Modified defined but not used
1531</artwork></figure></section>
1532<?ENDINC p4-conditional.abnf-appendix ?>
1533
1534<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
1535
1536<section title="Since RFC 2616">
1537<t>
1538  Extracted relevant partitions from <xref target="RFC2616"/>.
1539</t>
1540</section>
1541
1542<section title="Since draft-ietf-httpbis-p4-conditional-00">
1543<t>
1544  Closed issues:
1545  <list style="symbols"> 
1546    <t>
1547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
1548      "Normative and Informative references"
1549    </t>
1550  </list>
1551</t>
1552<t>
1553  Other changes:
1554  <list style="symbols"> 
1555    <t>
1556      Move definitions of 304 and 412 condition codes from Part2.
1557    </t>
1558  </list>
1559</t>
1560</section>
1561
1562<section title="Since draft-ietf-httpbis-p4-conditional-01">
1563<t>
1564  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
1565  <list style="symbols"> 
1566    <t>
1567      Add explicit references to BNF syntax and rules imported from other parts of the specification.
1568    </t>
1569  </list>
1570</t>
1571</section>
1572
1573<section title="Since draft-ietf-httpbis-p4-conditional-02" anchor="changes.since.02">
1574<t>
1575  Closed issues:
1576  <list style="symbols"> 
1577    <t>
1578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/116"/>:
1579      "Weak ETags on non-GET requests"
1580    </t>
1581  </list>
1582</t>
1583<t>
1584  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
1585  <list style="symbols"> 
1586    <t>
1587      Reference RFC 3984, and update header field registrations for header fields defined
1588      in this document.
1589    </t>
1590  </list>
1591</t>
1592</section>
1593
1594<section title="Since draft-ietf-httpbis-p4-conditional-03" anchor="changes.since.03">
1595<t>
1596  Closed issues:
1597  <list style="symbols"> 
1598    <t>
1599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/71"/>:
1600      "Examples for ETag matching"
1601    </t>
1602    <t>
1603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/124"/>:
1604      "'entity value' undefined"
1605    </t>
1606    <t>
1607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/126"/>:
1608      "bogus 2068 Date header reference"
1609    </t>
1610  </list>
1611</t>
1612</section>
1613
1614<section title="Since draft-ietf-httpbis-p4-conditional-04" anchor="changes.since.04">
1615<t>
1616  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
1617  <list style="symbols"> 
1618    <t>
1619      Use "/" instead of "|" for alternatives.
1620    </t>
1621    <t>
1622      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
1623      whitespace ("OWS") and required whitespace ("RWS").
1624    </t>
1625    <t>
1626      Rewrite ABNFs to spell out whitespace rules, factor out
1627      header field value format definitions.
1628    </t>
1629  </list>
1630</t>
1631</section>
1632
1633<section title="Since draft-ietf-httpbis-p4-conditional-05" anchor="changes.since.05">
1634<t>
1635  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
1636  <list style="symbols"> 
1637    <t>
1638      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
1639    </t>
1640  </list>
1641</t>
1642</section>
1643
1644<section title="Since draft-ietf-httpbis-p4-conditional-06" anchor="changes.since.06">
1645<t>
1646  Closed issues:
1647  <list style="symbols"> 
1648    <t>
1649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/153"/>:
1650      "case-sensitivity of etag weakness indicator"
1651    </t>
1652  </list>
1653</t>
1654</section>
1655
1656<section title="Since draft-ietf-httpbis-p4-conditional-07" anchor="changes.since.07">
1657<t>
1658  Closed issues:
1659  <list style="symbols"> 
1660    <t>
1661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/116"/>:
1662      "Weak ETags on non-GET requests" (If-Match still was defined to require
1663      strong matching)
1664    </t>
1665    <t>
1666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
1667      "move IANA registrations for optional status codes"
1668    </t>
1669  </list>
1670</t>
1671</section>
1672
1673<section title="Since draft-ietf-httpbis-p4-conditional-08" anchor="changes.since.08">
1674<t>
1675  No significant changes.
1676</t>
1677</section>
1678
1679<section title="Since draft-ietf-httpbis-p4-conditional-09" anchor="changes.since.09">
1680<t>
1681  No significant changes.
1682</t>
1683</section>
1684
1685<section title="Since draft-ietf-httpbis-p4-conditional-10" anchor="changes.since.10">
1686<t>
1687  Closed issues:
1688  <list style="symbols"> 
1689    <t>
1690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
1691      "Clarify 'Requested Variant'"
1692    </t>
1693    <t>
1694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
1695      "Clarify entity / representation / variant terminology"
1696    </t>
1697    <t>
1698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
1699      "consider removing the 'changes from 2068' sections"
1700    </t>
1701  </list>
1702</t>
1703</section>
1704
1705<section title="Since draft-ietf-httpbis-p4-conditional-11" anchor="changes.since.11">
1706<t>
1707  None.
1708</t>
1709</section>
1710
1711<section title="Since draft-ietf-httpbis-p4-conditional-12" anchor="changes.since.12">
1712<t>
1713  Closed issues:
1714  <list style="symbols"> 
1715    <t>
1716      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
1717      "Header Classification"
1718    </t>
1719  </list>
1720</t>
1721</section>
1722
1723<section title="Since draft-ietf-httpbis-p4-conditional-13" anchor="changes.since.13">
1724<t>
1725  Closed issues:
1726  <list style="symbols"> 
1727    <t>
1728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/89"/>:
1729      "If-* and entities"
1730    </t>
1731    <t>
1732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/101"/>:
1733      "Definition of validator weakness"
1734    </t>
1735    <t>
1736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
1737      "untangle ABNFs for header fields"
1738    </t>
1739    <t>
1740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/269"/>:
1741      "ETags and Quotes"
1742    </t>
1743  </list>
1744</t>
1745</section>
1746
1747<section title="Since draft-ietf-httpbis-p4-conditional-14" anchor="changes.since.14">
1748<t>
1749  None.
1750</t>
1751</section>
1752
1753<section title="Since draft-ietf-httpbis-p4-conditional-15" anchor="changes.since.15">
1754<t>
1755  Closed issues:
1756  <list style="symbols"> 
1757    <t>
1758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/304"/>:
1759      "If-Range should be listed when dicussing contexts where L-M can be considered strong"
1760    </t>
1761  </list>
1762</t>
1763</section>
1764
1765</section>
1766
1767</back>
1768</rfc>
Note: See TracBrowser for help on using the repository browser.