source: draft-ietf-httpbis/latest/p5-range.xml @ 150

Last change on this file since 150 was 150, checked in by julian.reschke@…, 12 years ago

do not say "obsoletes 2068"; this is implied by the fact that we obsolete 2616, which in turn obsoleted 2068.

  • Property svn:eol-style set to native
File size: 46.4 KB
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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 "January">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY weak-and-strong-validators "<xref target='Part4' x:rel='#weak.and.strong.validators' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19]>
20<?rfc toc="yes" ?>
21<?rfc symrefs="yes" ?>
22<?rfc sortrefs="yes" ?>
23<?rfc compact="yes"?>
24<?rfc subcompact="no" ?>
25<?rfc linkmailto="no" ?>
26<?rfc editing="no" ?>
27<?rfc-ext allow-markup-in-artwork="yes" ?>
28<?rfc-ext include-references-in-index="yes" ?>
29<rfc obsoletes="2616" category="std"
30     ipr="full3978" docName="draft-ietf-httpbis-p5-range-&ID-VERSION;"
31     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
32<front>
33
34  <title abbrev="HTTP/1.1, Part 5">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
35
36  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
37    <organization abbrev="Day Software">Day Software</organization>
38    <address>
39      <postal>
40        <street>23 Corporate Plaza DR, Suite 280</street>
41        <city>Newport Beach</city>
42        <region>CA</region>
43        <code>92660</code>
44        <country>USA</country>
45      </postal>
46      <phone>+1-949-706-5300</phone>
47      <facsimile>+1-949-706-5305</facsimile>
48      <email>fielding@gbiv.com</email>
49      <uri>http://roy.gbiv.com/</uri>
50    </address>
51  </author>
52
53  <author initials="J." surname="Gettys" fullname="Jim Gettys">
54    <organization>One Laptop per Child</organization>
55    <address>
56      <postal>
57        <street>21 Oak Knoll Road</street>
58        <city>Carlisle</city>
59        <region>MA</region>
60        <code>01741</code>
61        <country>USA</country>
62      </postal>
63      <email>jg@laptop.org</email>
64      <uri>http://www.laptop.org/</uri>
65    </address>
66  </author>
67 
68  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
69    <organization abbrev="HP">Hewlett-Packard Company</organization>
70    <address>
71      <postal>
72        <street>HP Labs, Large Scale Systems Group</street>
73        <street>1501 Page Mill Road, MS 1177</street>
74        <city>Palo Alto</city>
75        <region>CA</region>
76        <code>94304</code>
77        <country>USA</country>
78      </postal>
79      <email>JeffMogul@acm.org</email>
80    </address>
81  </author>
82
83  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
84    <organization abbrev="Microsoft">Microsoft Corporation</organization>
85    <address>
86      <postal>
87        <street>1 Microsoft Way</street>
88        <city>Redmond</city>
89        <region>WA</region>
90        <code>98052</code>
91        <country>USA</country>
92      </postal>
93      <email>henrikn@microsoft.com</email>
94    </address>
95  </author>
96
97  <author initials="L." surname="Masinter" fullname="Larry Masinter">
98    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
99    <address>
100      <postal>
101        <street>345 Park Ave</street>
102        <city>San Jose</city>
103        <region>CA</region>
104        <code>95110</code>
105        <country>USA</country>
106      </postal>
107      <email>LMM@acm.org</email>
108      <uri>http://larry.masinter.net/</uri>
109    </address>
110  </author>
111 
112  <author initials="P." surname="Leach" fullname="Paul J. Leach">
113    <organization abbrev="Microsoft">Microsoft Corporation</organization>
114    <address>
115      <postal>
116        <street>1 Microsoft Way</street>
117        <city>Redmond</city>
118        <region>WA</region>
119        <code>98052</code>
120      </postal>
121      <email>paulle@microsoft.com</email>
122    </address>
123  </author>
124   
125  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
126    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
127    <address>
128      <postal>
129        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
130        <street>The Stata Center, Building 32</street>
131        <street>32 Vassar Street</street>
132        <city>Cambridge</city>
133        <region>MA</region>
134        <code>02139</code>
135        <country>USA</country>
136      </postal>
137      <email>timbl@w3.org</email>
138      <uri>http://www.w3.org/People/Berners-Lee/</uri>
139    </address>
140  </author>
141
142  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
143    <organization abbrev="W3C">World Wide Web Consortium</organization>
144    <address>
145      <postal>
146        <street>W3C / ERCIM</street>
147        <street>2004, rte des Lucioles</street>
148        <city>Sophia-Antipolis</city>
149        <region>AM</region>
150        <code>06902</code>
151        <country>France</country>
152      </postal>
153      <email>ylafon@w3.org</email>
154      <uri>http://www.raubacapeu.net/people/yves/</uri>
155    </address>
156  </author>
157
158  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
159    <organization abbrev="greenbytes">greenbytes GmbH</organization>
160    <address>
161      <postal>
162        <street>Hafenweg 16</street>
163        <city>Muenster</city><region>NW</region><code>48155</code>
164        <country>Germany</country>
165      </postal>
166      <phone>+49 251 2807760</phone>   
167      <facsimile>+49 251 2807761</facsimile>   
168      <email>julian.reschke@greenbytes.de</email>       
169      <uri>http://greenbytes.de/tech/webdav/</uri>     
170    </address>
171  </author>
172
173  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
174
175<abstract>
176<t>
177   The Hypertext Transfer Protocol (HTTP) is an application-level
178   protocol for distributed, collaborative, hypermedia information
179   systems. HTTP has been in use by the World Wide Web global information
180   initiative since 1990. This document is Part 5 of the seven-part specification
181   that defines the protocol referred to as "HTTP/1.1" and, taken together,
182   obsoletes RFC 2616.  Part 5 defines range-specific requests and
183   the rules for constructing and combining responses to those requests.
184</t>
185</abstract>
186
187<note title="Editorial Note (To be removed by RFC Editor)">
188  <t>
189    Discussion of this draft should take place on the HTTPBIS working group
190    mailing list (ietf-http-wg@w3.org). The current issues list is
191    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
192    and related documents (including fancy diffs) can be found at
193    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
194  </t>
195</note>
196</front>
197<middle>
198<section title="Introduction" anchor="introduction">
199<t>
200   This document will define aspects of HTTP related to range requests,
201   partial responses, and the multipart/byteranges media type.  Right now
202   it only includes the extracted relevant sections of
203   <xref target="RFC2616">RFC 2616</xref> without edit.
204</t>
205
206<section title="Requirements" anchor="intro.requirements">
207<t>
208   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
209   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
210   document are to be interpreted as described in <xref target="RFC2119"/>.
211</t>
212<t>
213   An implementation is not compliant if it fails to satisfy one or more
214   of the &MUST; or &REQUIRED; level requirements for the protocols it
215   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
216   level and all the &SHOULD; level requirements for its protocols is said
217   to be "unconditionally compliant"; one that satisfies all the &MUST;
218   level requirements but not all the &SHOULD; level requirements for its
219   protocols is said to be "conditionally compliant."
220</t>
221</section>
222</section>
223
224<section title="Range Units" anchor="range.units">
225<t>
226   HTTP/1.1 allows a client to request that only part (a range of) the
227   response entity be included within the response. HTTP/1.1 uses range
228   units in the Range (<xref target="header.range"/>) and Content-Range (<xref target="header.content-range"/>)
229   header fields. An entity can be broken down into subranges according
230   to various structural units.
231</t>
232<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="range-unit"/><iref primary="true" item="Grammar" subitem="bytes-unit"/><iref primary="true" item="Grammar" subitem="other-range-unit"/>
233  range-unit       = bytes-unit | other-range-unit
234  bytes-unit       = "bytes"
235  other-range-unit = token
236</artwork></figure>
237<t>
238   The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
239   implementations &MAY; ignore ranges specified using other units.
240</t>
241<t>
242   HTTP/1.1 has been designed to allow implementations of applications
243   that do not depend on knowledge of ranges.
244</t>
245</section>
246
247<section title="Status Code Definitions">
248<section title="206 Partial Content" anchor="status.206">
249  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
250  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
251<t>
252   The server has fulfilled the partial GET request for the resource.
253   The request &MUST; have included a Range header field (<xref target="header.range"/>)
254   indicating the desired range, and &MAY; have included an If-Range
255   header field (<xref target="header.if-range"/>) to make the request conditional.
256</t>
257<t>
258   The response &MUST; include the following header fields:
259  <list style="symbols">
260    <t>
261        Either a Content-Range header field (<xref target="header.content-range"/>) indicating
262        the range included with this response, or a multipart/byteranges
263        Content-Type including Content-Range fields for each part. If a
264        Content-Length header field is present in the response, its
265        value &MUST; match the actual number of OCTETs transmitted in the
266        message-body.
267    </t>
268    <t>
269        Date
270    </t>
271    <t>
272        ETag and/or Content-Location, if the header would have been sent
273        in a 200 response to the same request
274    </t>
275    <t>
276        Expires, Cache-Control, and/or Vary, if the field-value might
277        differ from that sent in any previous response for the same
278        variant
279    </t>
280  </list>
281</t>
282<t>
283   If the 206 response is the result of an If-Range request, the response
284   &SHOULD-NOT; include other entity-headers. Otherwise, the response
285   &MUST; include all of the entity-headers that would have been returned
286   with a 200 (OK) response to the same request.
287</t>
288<t>
289   A cache &MUST-NOT; combine a 206 response with other previously cached
290   content if the ETag or Last-Modified headers do not match exactly,
291   see <xref target="combining.byte.ranges"/>.
292</t>
293<t>
294   A cache that does not support the Range and Content-Range headers
295   &MUST-NOT; cache 206 (Partial Content) responses.
296</t>
297</section>
298
299<section title="416 Requested Range Not Satisfiable" anchor="status.416">
300  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
301  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
302<t>
303   A server &SHOULD; return a response with this status code if a request
304   included a Range request-header field (<xref target="header.range"/>), and none of
305   the range-specifier values in this field overlap the current extent
306   of the selected resource, and the request did not include an If-Range
307   request-header field. (For byte-ranges, this means that the first-byte-pos
308   of all of the byte-range-spec values were greater than the
309   current length of the selected resource.)
310</t>
311<t>
312   When this status code is returned for a byte-range request, the
313   response &SHOULD; include a Content-Range entity-header field
314   specifying the current length of the selected resource (see <xref target="header.content-range"/>).
315   This response &MUST-NOT; use the multipart/byteranges content-type.
316</t>
317</section>
318</section>
319
320<section title="Combining Byte Ranges" anchor="combining.byte.ranges">
321<t>
322   A response might transfer only a subrange of the bytes of an entity-body,
323   either because the request included one or more Range
324   specifications, or because a connection was broken prematurely. After
325   several such transfers, a cache might have received several ranges of
326   the same entity-body.
327</t>
328<t>
329   If a cache has a stored non-empty set of subranges for an entity, and
330   an incoming response transfers another subrange, the cache &MAY;
331   combine the new subrange with the existing set if both the following
332   conditions are met:
333  <list style="symbols">
334    <t>Both the incoming response and the cache entry have a cache
335        validator.</t>
336    <t>The two cache validators match using the strong comparison
337        function (see &weak-and-strong-validators;).</t>
338  </list>
339</t>
340<t>
341   If either requirement is not met, the cache &MUST; use only the most
342   recent partial response (based on the Date values transmitted with
343   every response, and using the incoming response if these values are
344   equal or missing), and &MUST; discard the other partial information.
345</t>
346</section>
347
348<section title="Header Field Definitions" anchor="header.fields">
349<t>
350   This section defines the syntax and semantics of HTTP/1.1 header fields
351   related to range requests and partial responses.
352</t>
353<t>
354   For entity-header fields, both sender and recipient refer to either the
355   client or the server, depending on who sends and who receives the entity.
356</t>
357
358<section title="Accept-Ranges" anchor="header.accept-ranges">
359  <iref primary="true" item="Accept-Ranges header" x:for-anchor=""/>
360  <iref primary="true" item="Headers" subitem="Accept-Ranges" x:for-anchor=""/>
361<t>
362      The Accept-Ranges response-header field allows the server to
363      indicate its acceptance of range requests for a resource:
364</t>
365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Ranges"/><iref primary="true" item="Grammar" subitem="acceptable-ranges"/>
366  Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
367  acceptable-ranges = 1#range-unit | "none"
368</artwork></figure>
369<t>
370      Origin servers that accept byte-range requests &MAY; send
371</t>
372<figure><artwork type="example">
373       Accept-Ranges: bytes
374</artwork></figure>
375<t>
376      but are not required to do so. Clients &MAY; generate byte-range
377      requests without having received this header for the resource
378      involved. Range units are defined in <xref target="range.units"/>.
379</t>
380<t>
381      Servers that do not accept any kind of range request for a
382      resource &MAY; send
383</t>
384<figure><artwork type="example">
385       Accept-Ranges: none
386</artwork></figure>
387<t>
388      to advise the client not to attempt a range request.
389</t>
390</section>
391
392<section title="Content-Range" anchor="header.content-range">
393  <iref primary="true" item="Content-Range header" x:for-anchor=""/>
394  <iref primary="true" item="Headers" subitem="Content-Range" x:for-anchor=""/>
395<t>
396   The Content-Range entity-header is sent with a partial entity-body to
397   specify where in the full entity-body the partial body should be
398   applied. Range units are defined in <xref target="range.units"/>.
399</t>
400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Range"/><iref primary="true" item="Grammar" subitem="content-range-spec"/><iref primary="true" item="Grammar" subitem="byte-content-range-spec"/><iref primary="true" item="Grammar" subitem="byte-range-resp-spec"/><iref primary="true" item="Grammar" subitem="instance-length"/>
401  Content-Range = "Content-Range" ":" content-range-spec
402 
403  content-range-spec      = byte-content-range-spec
404  byte-content-range-spec = bytes-unit SP
405                            byte-range-resp-spec "/"
406                            ( instance-length | "*" )
407 
408  byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
409                                 | "*"
410  instance-length           = 1*DIGIT
411</artwork></figure>
412<t>
413   The header &SHOULD; indicate the total length of the full entity-body,
414   unless this length is unknown or difficult to determine. The asterisk
415   "*" character means that the instance-length is unknown at the time
416   when the response was generated.
417</t>
418<t>
419   Unlike byte-ranges-specifier values (see <xref target="byte.ranges"/>), a byte-range-resp-spec
420   &MUST; only specify one range, and &MUST; contain
421   absolute byte positions for both the first and last byte of the
422   range.
423</t>
424<t>
425   A byte-content-range-spec with a byte-range-resp-spec whose last-byte-pos
426   value is less than its first-byte-pos value, or whose
427   instance-length value is less than or equal to its last-byte-pos
428   value, is invalid. The recipient of an invalid byte-content-range-spec
429   &MUST; ignore it and any content transferred along with it.
430</t>
431<t>
432   A server sending a response with status code 416 (Requested range not
433   satisfiable) &SHOULD; include a Content-Range field with a byte-range-resp-spec
434   of "*". The instance-length specifies the current length of
435   the selected resource. A response with status code 206 (Partial
436   Content) &MUST-NOT; include a Content-Range field with a byte-range-resp-spec of "*".
437</t>
438<t>
439   Examples of byte-content-range-spec values, assuming that the entity
440   contains a total of 1234 bytes:
441   <list style="symbols">
442      <t>
443        The first 500 bytes:
444<figure><artwork type="text/plain">
445   bytes 0-499/1234
446</artwork></figure>
447      </t>   
448      <t>
449        The second 500 bytes:
450<figure><artwork type="text/plain">
451   bytes 500-999/1234
452</artwork></figure>
453      </t>   
454      <t>
455        All except for the first 500 bytes:
456<figure><artwork type="text/plain">
457   bytes 500-1233/1234
458</artwork></figure>
459      </t>   
460      <t>
461        The last 500 bytes:
462<figure><artwork type="text/plain">
463   bytes 734-1233/1234
464</artwork></figure>
465      </t>   
466   </list>
467</t>
468<t>
469   When an HTTP message includes the content of a single range (for
470   example, a response to a request for a single range, or to a request
471   for a set of ranges that overlap without any holes), this content is
472   transmitted with a Content-Range header, and a Content-Length header
473   showing the number of bytes actually transferred. For example,
474</t>
475<figure><artwork type="example">
476    HTTP/1.1 206 Partial Content
477    Date: Wed, 15 Nov 1995 06:25:24 GMT
478    Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
479    Content-Range: bytes 21010-47021/47022
480    Content-Length: 26012
481    Content-Type: image/gif
482</artwork></figure>
483<t>
484   When an HTTP message includes the content of multiple ranges (for
485   example, a response to a request for multiple non-overlapping
486   ranges), these are transmitted as a multipart message. The multipart
487   media type used for this purpose is "multipart/byteranges" as defined
488   in <xref target="internet.media.type.multipart.byteranges"/>. See <xref target="changes.from.rfc.2068"/> for a compatibility issue.
489</t>
490<t>
491   A response to a request for a single range &MUST-NOT; be sent using the
492   multipart/byteranges media type.  A response to a request for
493   multiple ranges, whose result is a single range, &MAY; be sent as a
494   multipart/byteranges media type with one part. A client that cannot
495   decode a multipart/byteranges message &MUST-NOT; ask for multiple
496   byte-ranges in a single request.
497</t>
498<t>
499   When a client requests multiple byte-ranges in one request, the
500   server &SHOULD; return them in the order that they appeared in the
501   request.
502</t>
503<t>
504   If the server ignores a byte-range-spec because it is syntactically
505   invalid, the server &SHOULD; treat the request as if the invalid Range
506   header field did not exist. (Normally, this means return a 200
507   response containing the full entity).
508</t>
509<t>
510   If the server receives a request (other than one including an If-Range
511   request-header field) with an unsatisfiable Range request-header
512   field (that is, all of whose byte-range-spec values have a
513   first-byte-pos value greater than the current length of the selected
514   resource), it &SHOULD; return a response code of 416 (Requested range
515   not satisfiable) (<xref target="status.416"/>).
516  <list><t>
517      <x:h>Note:</x:h> clients cannot depend on servers to send a 416 (Requested
518      range not satisfiable) response instead of a 200 (OK) response for
519      an unsatisfiable Range request-header, since not all servers
520      implement this request-header.
521  </t></list>
522</t>
523</section>
524
525<section title="If-Range" anchor="header.if-range">
526  <iref primary="true" item="If-Range header" x:for-anchor=""/>
527  <iref primary="true" item="Headers" subitem="If-Range" x:for-anchor=""/>
528<t>
529   If a client has a partial copy of an entity in its cache, and wishes
530   to have an up-to-date copy of the entire entity in its cache, it
531   could use the Range request-header with a conditional GET (using
532   either or both of If-Unmodified-Since and If-Match.) However, if the
533   condition fails because the entity has been modified, the client
534   would then have to make a second request to obtain the entire current
535   entity-body.
536</t>
537<t>
538   The If-Range header allows a client to "short-circuit" the second
539   request. Informally, its meaning is `if the entity is unchanged, send
540   me the part(s) that I am missing; otherwise, send me the entire new
541   entity'.
542</t>
543<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Range"/>
544  If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
545</artwork></figure>
546<t>
547   If the client has no entity tag for an entity, but does have a Last-Modified
548   date, it &MAY; use that date in an If-Range header. (The
549   server can distinguish between a valid HTTP-date and any form of
550   entity-tag by examining no more than two characters.) The If-Range
551   header &SHOULD; only be used together with a Range header, and &MUST; be
552   ignored if the request does not include a Range header, or if the
553   server does not support the sub-range operation.
554</t>
555<t>
556   If the entity tag given in the If-Range header matches the current
557   entity tag for the entity, then the server &SHOULD; provide the
558   specified sub-range of the entity using a 206 (Partial Content)
559   response. If the entity tag does not match, then the server &SHOULD;
560   return the entire entity using a 200 (OK) response.
561</t>
562</section>
563
564<section title="Range" anchor="header.range">
565  <iref primary="true" item="Range header" x:for-anchor=""/>
566  <iref primary="true" item="Headers" subitem="Range" x:for-anchor=""/>
567
568<section title="Byte Ranges" anchor="byte.ranges">
569<t>
570   Since all HTTP entities are represented in HTTP messages as sequences
571   of bytes, the concept of a byte range is meaningful for any HTTP
572   entity. (However, not all clients and servers need to support byte-range
573   operations.)
574</t>
575<t>
576   Byte range specifications in HTTP apply to the sequence of bytes in
577   the entity-body (not necessarily the same as the message-body).
578</t>
579<t>
580   A byte range operation &MAY; specify a single range of bytes, or a set
581   of ranges within a single entity.
582</t>
583<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="ranges-specifier"/><iref primary="true" item="Grammar" subitem="byte-ranges-specifier"/><iref primary="true" item="Grammar" subitem="byte-range-set"/><iref primary="true" item="Grammar" subitem="byte-range-spec"/><iref primary="true" item="Grammar" subitem="first-byte-pos"/><iref primary="true" item="Grammar" subitem="last-byte-pos"/>
584  ranges-specifier = byte-ranges-specifier
585  byte-ranges-specifier = bytes-unit "=" byte-range-set
586  byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
587  byte-range-spec = first-byte-pos "-" [last-byte-pos]
588  first-byte-pos  = 1*DIGIT
589  last-byte-pos   = 1*DIGIT
590</artwork></figure>
591<t>
592   The first-byte-pos value in a byte-range-spec gives the byte-offset
593   of the first byte in a range. The last-byte-pos value gives the
594   byte-offset of the last byte in the range; that is, the byte
595   positions specified are inclusive. Byte offsets start at zero.
596</t>
597<t>
598   If the last-byte-pos value is present, it &MUST; be greater than or
599   equal to the first-byte-pos in that byte-range-spec, or the byte-range-spec
600   is syntactically invalid. The recipient of a byte-range-set
601   that includes one or more syntactically invalid byte-range-spec
602   values &MUST; ignore the header field that includes that byte-range-set.
603</t>
604<t>
605   If the last-byte-pos value is absent, or if the value is greater than
606   or equal to the current length of the entity-body, last-byte-pos is
607   taken to be equal to one less than the current length of the entity-body
608   in bytes.
609</t>
610<t>
611   By its choice of last-byte-pos, a client can limit the number of
612   bytes retrieved without knowing the size of the entity.
613</t>
614<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="suffix-byte-range-spec"/><iref primary="true" item="Grammar" subitem="suffix-length"/>
615  suffix-byte-range-spec = "-" suffix-length
616  suffix-length = 1*DIGIT
617</artwork></figure>
618<t>
619   A suffix-byte-range-spec is used to specify the suffix of the
620   entity-body, of a length given by the suffix-length value. (That is,
621   this form specifies the last N bytes of an entity-body.) If the
622   entity is shorter than the specified suffix-length, the entire
623   entity-body is used.
624</t>
625<t>
626   If a syntactically valid byte-range-set includes at least one byte-range-spec
627   whose first-byte-pos is less than the current length of
628   the entity-body, or at least one suffix-byte-range-spec with a non-zero
629   suffix-length, then the byte-range-set is satisfiable.
630   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
631   is unsatisfiable, the server &SHOULD; return a response with a status
632   of 416 (Requested range not satisfiable). Otherwise, the server
633   &SHOULD; return a response with a status of 206 (Partial Content)
634   containing the satisfiable ranges of the entity-body.
635</t>
636<t>
637   Examples of byte-ranges-specifier values (assuming an entity-body of
638   length 10000):
639  <list style="symbols">
640     <t>The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-499</t>
641
642     <t>The second 500 bytes (byte offsets 500-999, inclusive):
643        bytes=500-999</t>
644
645     <t>The final 500 bytes (byte offsets 9500-9999, inclusive):
646        bytes=-500</t>
647
648     <t>Or bytes=9500-</t>
649
650     <t>The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1</t>
651
652     <t>Several legal but not canonical specifications of the second 500
653        bytes (byte offsets 500-999, inclusive):
654        <vspace/>
655         bytes=500-600,601-999<vspace/>
656         bytes=500-700,601-999</t>
657  </list>
658</t>
659</section>
660
661<section title="Range Retrieval Requests" anchor="range.retrieval.requests">
662<t>
663   HTTP retrieval requests using conditional or unconditional GET
664   methods &MAY; request one or more sub-ranges of the entity, instead of
665   the entire entity, using the Range request header, which applies to
666   the entity returned as the result of the request:
667</t>
668<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Range"/>
669  Range = "Range" ":" ranges-specifier
670</artwork></figure>
671<t>
672   A server &MAY; ignore the Range header. However, HTTP/1.1 origin
673   servers and intermediate caches ought to support byte ranges when
674   possible, since Range supports efficient recovery from partially
675   failed transfers, and supports efficient partial retrieval of large
676   entities.
677</t>
678<t>
679   If the server supports the Range header and the specified range or
680   ranges are appropriate for the entity:
681  <list style="symbols">
682     <t>The presence of a Range header in an unconditional GET modifies
683        what is returned if the GET is otherwise successful. In other
684        words, the response carries a status code of 206 (Partial
685        Content) instead of 200 (OK).</t>
686
687     <t>The presence of a Range header in a conditional GET (a request
688        using one or both of If-Modified-Since and If-None-Match, or
689        one or both of If-Unmodified-Since and If-Match) modifies what
690        is returned if the GET is otherwise successful and the
691        condition is true. It does not affect the 304 (Not Modified)
692        response returned if the conditional is false.</t>
693  </list>
694</t>
695<t>
696   In some cases, it might be more appropriate to use the If-Range
697   header (see <xref target="header.if-range"/>) in addition to the Range header.
698</t>
699<t>
700   If a proxy that supports ranges receives a Range request, forwards
701   the request to an inbound server, and receives an entire entity in
702   reply, it &SHOULD; only return the requested range to its client. It
703   &SHOULD; store the entire received response in its cache if that is
704   consistent with its cache allocation policies.
705</t>
706</section>
707</section>
708</section>
709
710<section title="IANA Considerations" anchor="IANA.considerations">
711<t>
712   TBD.
713</t>
714</section>
715
716<section title="Security Considerations" anchor="security.considerations">
717<t>
718   No additional security considerations have been identified beyond
719   those applicable to HTTP in general &messaging;.
720</t>
721</section>
722
723<section title="Acknowledgments" anchor="ack">
724<t>
725   Most of the specification of ranges is based on work originally done
726   by Ari Luotonen and John Franks, with additional input from Steve
727   Zilles.
728</t>
729</section>
730</middle>
731<back>
732
733<references title="Normative References">
734
735<reference anchor="Part1">
736  <front>
737    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
738    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
739      <organization abbrev="Day Software">Day Software</organization>
740      <address><email>fielding@gbiv.com</email></address>
741    </author>
742    <author initials="J." surname="Gettys" fullname="Jim Gettys">
743      <organization>One Laptop per Child</organization>
744      <address><email>jg@laptop.org</email></address>
745    </author>
746    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
747      <organization abbrev="HP">Hewlett-Packard Company</organization>
748      <address><email>JeffMogul@acm.org</email></address>
749    </author>
750    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
751      <organization abbrev="Microsoft">Microsoft Corporation</organization>
752      <address><email>henrikn@microsoft.com</email></address>
753    </author>
754    <author initials="L." surname="Masinter" fullname="Larry Masinter">
755      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
756      <address><email>LMM@acm.org</email></address>
757    </author>
758    <author initials="P." surname="Leach" fullname="Paul J. Leach">
759      <organization abbrev="Microsoft">Microsoft Corporation</organization>
760      <address><email>paulle@microsoft.com</email></address>
761    </author>
762    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
763      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
764      <address><email>timbl@w3.org</email></address>
765    </author>
766    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
767      <organization abbrev="W3C">World Wide Web Consortium</organization>
768      <address><email>ylafon@w3.org</email></address>
769    </author>
770    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
771      <organization abbrev="greenbytes">greenbytes GmbH</organization>
772      <address><email>julian.reschke@greenbytes.de</email></address>
773    </author>
774    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
775  </front>
776  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
777  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
778</reference>
779
780<reference anchor="Part3">
781  <front>
782    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
783    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
784      <organization abbrev="Day Software">Day Software</organization>
785      <address><email>fielding@gbiv.com</email></address>
786    </author>
787    <author initials="J." surname="Gettys" fullname="Jim Gettys">
788      <organization>One Laptop per Child</organization>
789      <address><email>jg@laptop.org</email></address>
790    </author>
791    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
792      <organization abbrev="HP">Hewlett-Packard Company</organization>
793      <address><email>JeffMogul@acm.org</email></address>
794    </author>
795    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
796      <organization abbrev="Microsoft">Microsoft Corporation</organization>
797      <address><email>henrikn@microsoft.com</email></address>
798    </author>
799    <author initials="L." surname="Masinter" fullname="Larry Masinter">
800      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
801      <address><email>LMM@acm.org</email></address>
802    </author>
803    <author initials="P." surname="Leach" fullname="Paul J. Leach">
804      <organization abbrev="Microsoft">Microsoft Corporation</organization>
805      <address><email>paulle@microsoft.com</email></address>
806    </author>
807    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
808      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
809      <address><email>timbl@w3.org</email></address>
810    </author>
811    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
812      <organization abbrev="W3C">World Wide Web Consortium</organization>
813      <address><email>ylafon@w3.org</email></address>
814    </author>
815    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
816      <organization abbrev="greenbytes">greenbytes GmbH</organization>
817      <address><email>julian.reschke@greenbytes.de</email></address>
818    </author>
819    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
820  </front>
821  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
822  <x:source href="p3-payload.xml" basename="p3-payload"/>
823</reference>
824
825<reference anchor="Part4">
826  <front>
827    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
828    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
829      <organization abbrev="Day Software">Day Software</organization>
830      <address><email>fielding@gbiv.com</email></address>
831    </author>
832    <author initials="J." surname="Gettys" fullname="Jim Gettys">
833      <organization>One Laptop per Child</organization>
834      <address><email>jg@laptop.org</email></address>
835    </author>
836    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
837      <organization abbrev="HP">Hewlett-Packard Company</organization>
838      <address><email>JeffMogul@acm.org</email></address>
839    </author>
840    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
841      <organization abbrev="Microsoft">Microsoft Corporation</organization>
842      <address><email>henrikn@microsoft.com</email></address>
843    </author>
844    <author initials="L." surname="Masinter" fullname="Larry Masinter">
845      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
846      <address><email>LMM@acm.org</email></address>
847    </author>
848    <author initials="P." surname="Leach" fullname="Paul J. Leach">
849      <organization abbrev="Microsoft">Microsoft Corporation</organization>
850      <address><email>paulle@microsoft.com</email></address>
851    </author>
852    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
853      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
854      <address><email>timbl@w3.org</email></address>
855    </author>
856    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
857      <organization abbrev="W3C">World Wide Web Consortium</organization>
858      <address><email>ylafon@w3.org</email></address>
859    </author>
860    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
861      <organization abbrev="greenbytes">greenbytes GmbH</organization>
862      <address><email>julian.reschke@greenbytes.de</email></address>
863    </author>
864    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
865  </front>
866  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
867  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
868</reference>
869
870<reference anchor="Part6">
871  <front>
872    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
873    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
874      <organization abbrev="Day Software">Day Software</organization>
875      <address><email>fielding@gbiv.com</email></address>
876    </author>
877    <author initials="J." surname="Gettys" fullname="Jim Gettys">
878      <organization>One Laptop per Child</organization>
879      <address><email>jg@laptop.org</email></address>
880    </author>
881    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
882      <organization abbrev="HP">Hewlett-Packard Company</organization>
883      <address><email>JeffMogul@acm.org</email></address>
884    </author>
885    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
886      <organization abbrev="Microsoft">Microsoft Corporation</organization>
887      <address><email>henrikn@microsoft.com</email></address>
888    </author>
889    <author initials="L." surname="Masinter" fullname="Larry Masinter">
890      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
891      <address><email>LMM@acm.org</email></address>
892    </author>
893    <author initials="P." surname="Leach" fullname="Paul J. Leach">
894      <organization abbrev="Microsoft">Microsoft Corporation</organization>
895      <address><email>paulle@microsoft.com</email></address>
896    </author>
897    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
898      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
899      <address><email>timbl@w3.org</email></address>
900    </author>
901    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
902      <organization abbrev="W3C">World Wide Web Consortium</organization>
903      <address><email>ylafon@w3.org</email></address>
904    </author>
905    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
906      <organization abbrev="greenbytes">greenbytes GmbH</organization>
907      <address><email>julian.reschke@greenbytes.de</email></address>
908    </author>
909    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
910  </front>
911  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
912  <x:source href="p6-cache.xml" basename="p6-cache"/>
913</reference>
914
915<reference anchor="RFC2046">
916  <front>
917    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
918    <author initials="N." surname="Freed" fullname="Ned Freed">
919      <organization>Innosoft International, Inc.</organization>
920      <address><email>ned@innosoft.com</email></address>
921    </author>
922    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
923      <organization>First Virtual Holdings</organization>
924      <address><email>nsb@nsb.fv.com</email></address>
925    </author>
926    <date month="November" year="1996"/>
927  </front>
928  <seriesInfo name="RFC" value="2046"/>
929</reference>
930
931<reference anchor="RFC2119">
932  <front>
933    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
934    <author initials="S." surname="Bradner" fullname="Scott Bradner">
935      <organization>Harvard University</organization>
936      <address><email>sob@harvard.edu</email></address>
937    </author>
938    <date month="March" year="1997"/>
939  </front>
940  <seriesInfo name="BCP" value="14"/>
941  <seriesInfo name="RFC" value="2119"/>
942</reference>
943
944</references>
945
946<references title="Informative References">
947
948<reference anchor="RFC2616">
949  <front>
950    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
951    <author initials="R." surname="Fielding" fullname="R. Fielding">
952      <organization>University of California, Irvine</organization>
953      <address><email>fielding@ics.uci.edu</email></address>
954    </author>
955    <author initials="J." surname="Gettys" fullname="J. Gettys">
956      <organization>W3C</organization>
957      <address><email>jg@w3.org</email></address>
958    </author>
959    <author initials="J." surname="Mogul" fullname="J. Mogul">
960      <organization>Compaq Computer Corporation</organization>
961      <address><email>mogul@wrl.dec.com</email></address>
962    </author>
963    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
964      <organization>MIT Laboratory for Computer Science</organization>
965      <address><email>frystyk@w3.org</email></address>
966    </author>
967    <author initials="L." surname="Masinter" fullname="L. Masinter">
968      <organization>Xerox Corporation</organization>
969      <address><email>masinter@parc.xerox.com</email></address>
970    </author>
971    <author initials="P." surname="Leach" fullname="P. Leach">
972      <organization>Microsoft Corporation</organization>
973      <address><email>paulle@microsoft.com</email></address>
974    </author>
975    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
976      <organization>W3C</organization>
977      <address><email>timbl@w3.org</email></address>
978    </author>
979    <date month="June" year="1999"/>
980  </front>
981  <seriesInfo name="RFC" value="2616"/>
982</reference>
983
984</references>
985
986<section title="Internet Media Type multipart/byteranges" anchor="internet.media.type.multipart.byteranges">
987<iref item="Media Type" subitem="multipart/byteranges" primary="true"/>
988<iref item="multipart/byteranges Media Type" primary="true"/>
989<t>
990   When an HTTP 206 (Partial Content) response message includes the
991   content of multiple ranges (a response to a request for multiple
992   non-overlapping ranges), these are transmitted as a multipart
993   message-body. The media type for this purpose is called
994   "multipart/byteranges".
995</t><t>
996   The multipart/byteranges media type includes two or more parts, each
997   with its own Content-Type and Content-Range fields. The required
998   boundary parameter specifies the boundary string used to separate
999   each body-part.
1000</t>
1001<t>
1002  <list style="hanging" x:indent="12em">
1003    <t hangText="Media Type name:">
1004      multipart
1005    </t>
1006    <t hangText="Media subtype name:">
1007      byteranges
1008    </t>
1009    <t hangText="Required parameters:">
1010      boundary
1011    </t>
1012    <t hangText="Optional parameters:">
1013      none
1014    </t>
1015    <t hangText="Encoding considerations:">
1016      only "7bit", "8bit", or "binary" are permitted
1017    </t>
1018    <t hangText="Security considerations:">
1019      none
1020    </t>
1021  </list>
1022</t>
1023<figure><preamble>
1024   For example:
1025</preamble><artwork type="example">
1026   HTTP/1.1 206 Partial Content
1027   Date: Wed, 15 Nov 1995 06:25:24 GMT
1028   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
1029   Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
1030
1031   --THIS_STRING_SEPARATES
1032   Content-type: application/pdf
1033   Content-range: bytes 500-999/8000
1034
1035   ...the first range...
1036   --THIS_STRING_SEPARATES
1037   Content-type: application/pdf
1038   Content-range: bytes 7000-7999/8000
1039
1040   ...the second range
1041   --THIS_STRING_SEPARATES--
1042</artwork></figure>
1043<t>
1044      Notes:
1045  <list style="numbers">
1046      <t>Additional CRLFs may precede the first boundary string in the
1047         entity.</t>
1048
1049      <t>Although <xref target="RFC2046"/> permits the boundary string to be
1050         quoted, some existing implementations handle a quoted boundary
1051         string incorrectly.</t>
1052
1053      <t>A number of browsers and servers were coded to an early draft
1054         of the byteranges specification to use a media type of
1055         multipart/x-byteranges<iref item="multipart/x-byteranges Media Type"/><iref item="Media Type" subitem="multipart/x-byteranges"/>, which is almost, but not quite
1056         compatible with the version documented in HTTP/1.1.</t>
1057  </list>
1058</t>
1059</section>
1060
1061<section title="Compatibility with Previous Versions" anchor="compatibility">
1062<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
1063<t>
1064   Transfer-coding and message lengths all interact in ways that
1065   required fixing exactly when chunked encoding is used (to allow for
1066   transfer encoding that may not be self delimiting); it was important
1067   to straighten out exactly how message lengths are computed.
1068   (<xref target="header.content-range"/>,
1069   see also <xref target="Part1"/>, <xref target="Part3"/> and <xref target="Part6"/>)
1070</t>
1071<t>
1072   There are situations where a server (especially a proxy) does not
1073   know the full length of a response but is capable of serving a
1074   byterange request. We therefore need a mechanism to allow byteranges
1075   with a content-range not indicating the full length of the message.
1076   (<xref target="header.content-range"/>)
1077</t>
1078<t>
1079   Range request responses would become very verbose if all meta-data
1080   were always returned; by allowing the server to only send needed
1081   headers in a 206 response, this problem can be avoided.
1082   (Section <xref target="status.206" format="counter"/>
1083   and <xref target="header.if-range" format="counter"/>)
1084</t>
1085<t>
1086   Fix problem with unsatisfiable range requests; there are two cases:
1087   syntactic problems, and range doesn't exist in the document. The 416
1088   status code was needed to resolve this ambiguity needed to indicate
1089   an error for a byte range request that falls outside of the actual
1090   contents of a document. (Section <xref target="status.416" format="counter"/>, <xref target="header.content-range" format="counter"/>)
1091</t>
1092</section>
1093
1094<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
1095<t>
1096  Clarify that it is not ok to use a weak cache validator in a 206 response.
1097  (<xref target="status.206"/>)
1098</t>
1099</section>
1100
1101</section>
1102
1103<section title="Change Log (to be removed by RFC Editor before publication)">
1104
1105<section title="Since RFC2616">
1106<t>
1107  Extracted relevant partitions from <xref target="RFC2616"/>.
1108</t>
1109</section>
1110
1111<section title="Since draft-ietf-httpbis-p5-range-00">
1112<t>
1113  Closed issues:
1114  <list style="symbols"> 
1115    <t>
1116      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/18"/>:
1117      "Cache validators in 206 responses"
1118      (<eref target="http://purl.org/NET/http-errata#ifrange206"/>)
1119    </t>
1120    <t>
1121      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
1122      "Normative up-to-date references"
1123    </t>
1124  </list>
1125</t>
1126<t>
1127  Other changes:
1128  <list style="symbols">
1129    <t>
1130      Categorize references as "Normative" or "Informative".
1131    </t>
1132  </list>
1133</t>
1134</section>
1135
1136</section>
1137
1138</back>
1139</rfc>
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