draft-ietf-httpbis-p4-conditional-17.txt		draft-ietf-httpbis-p4-conditional-18.txt
	HTTPbis Working Group R. Fielding, Ed.		HTTPbis Working Group R. Fielding, Ed.
	Internet-Draft Adobe		Internet-Draft Adobe
	Obsoletes: 2616 (if approved) J. Gettys		Obsoletes: 2616 (if approved) J. Gettys
	Intended status: Standards Track Alcatel-Lucent		Intended status: Standards Track Alcatel-Lucent
	Expires: May 3, 2012 J. Mogul		Expires: July 7, 2012 J. Mogul
	HP		HP
	H. Frystyk		H. Frystyk
	Microsoft		Microsoft
	L. Masinter		L. Masinter
	Adobe		Adobe
	P. Leach		P. Leach
	Microsoft		Microsoft
	T. Berners-Lee		T. Berners-Lee
	W3C/MIT		W3C/MIT
	Y. Lafon, Ed.		Y. Lafon, Ed.
	W3C		W3C
	J. Reschke, Ed.		J. Reschke, Ed.
	greenbytes		greenbytes
	October 31, 2011		January 4, 2012
	HTTP/1.1, part 4: Conditional Requests		HTTP/1.1, part 4: Conditional Requests
	draft-ietf-httpbis-p4-conditional-17		draft-ietf-httpbis-p4-conditional-18
	Abstract		Abstract
	The Hypertext Transfer Protocol (HTTP) is an application-level		The Hypertext Transfer Protocol (HTTP) is an application-level
	protocol for distributed, collaborative, hypertext information		protocol for distributed, collaborative, hypertext information
	systems. HTTP has been in use by the World Wide Web global		systems. HTTP has been in use by the World Wide Web global
	information initiative since 1990. This document is Part 4 of the		information initiative since 1990. This document is Part 4 of the
	seven-part specification that defines the protocol referred to as		seven-part specification that defines the protocol referred to as
	"HTTP/1.1" and, taken together, obsoletes RFC 2616.		"HTTP/1.1" and, taken together, obsoletes RFC 2616.
	skipping to change at page 1, line 49		skipping to change at page 1, line 49
	Discussion of this draft should take place on the HTTPBIS working		Discussion of this draft should take place on the HTTPBIS working
	group mailing list (ietf-http-wg@w3.org), which is archived at		group mailing list (ietf-http-wg@w3.org), which is archived at
	<http://lists.w3.org/Archives/Public/ietf-http-wg/>.		<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
	The current issues list is at		The current issues list is at
	<http://tools.ietf.org/wg/httpbis/trac/report/3> and related		<http://tools.ietf.org/wg/httpbis/trac/report/3> and related
	documents (including fancy diffs) can be found at		documents (including fancy diffs) can be found at
	<http://tools.ietf.org/wg/httpbis/>.		<http://tools.ietf.org/wg/httpbis/>.
	The changes in this draft are summarized in Appendix C.18.		The changes in this draft are summarized in Appendix C.19.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on May 3, 2012.		This Internet-Draft will expire on July 7, 2012.
	Copyright Notice		Copyright Notice
	Copyright (c) 2011 IETF Trust and the persons identified as the		Copyright (c) 2012 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	skipping to change at page 3, line 12		skipping to change at page 3, line 12
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
	1.1. Conformance and Error Handling . . . . . . . . . . . . . . 5		1.1. Conformance and Error Handling . . . . . . . . . . . . . . 5
	1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6		1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
	2. Validators . . . . . . . . . . . . . . . . . . . . . . . . . . 6		2. Validators . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	2.1. Weak versus Strong . . . . . . . . . . . . . . . . . . . . 6		2.1. Weak versus Strong . . . . . . . . . . . . . . . . . . . . 6
	2.2. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 8		2.2. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 8
	2.2.1. Generation . . . . . . . . . . . . . . . . . . . . . . 8		2.2.1. Generation . . . . . . . . . . . . . . . . . . . . . . 8
	2.2.2. Comparison . . . . . . . . . . . . . . . . . . . . . . 9		2.2.2. Comparison . . . . . . . . . . . . . . . . . . . . . . 9
	2.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 10		2.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
	2.3.1. Generation . . . . . . . . . . . . . . . . . . . . . . 11		2.3.1. Generation . . . . . . . . . . . . . . . . . . . . . . 11
	2.3.2. Comparison . . . . . . . . . . . . . . . . . . . . . . 11		2.3.2. Comparison . . . . . . . . . . . . . . . . . . . . . . 12
	2.3.3. Example: Entity-tags varying on Content-Negotiated		2.3.3. Example: Entity-tags varying on Content-Negotiated
	Resources . . . . . . . . . . . . . . . . . . . . . . 12		Resources . . . . . . . . . . . . . . . . . . . . . . 12
	2.4. Rules for When to Use Entity-tags and Last-Modified		2.4. Rules for When to Use Entity-tags and Last-Modified
	Dates . . . . . . . . . . . . . . . . . . . . . . . . . . 13		Dates . . . . . . . . . . . . . . . . . . . . . . . . . . 13
	3. Precondition Header Fields . . . . . . . . . . . . . . . . . . 14		3. Precondition Header Fields . . . . . . . . . . . . . . . . . . 15
	3.1. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 15		3.1. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 15
	3.2. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 15		3.2. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 16
	3.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 17		3.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 17
	3.4. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 18		3.4. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 18
	3.5. If-Range . . . . . . . . . . . . . . . . . . . . . . . . . 19		3.5. If-Range . . . . . . . . . . . . . . . . . . . . . . . . . 19
	4. Status Code Definitions . . . . . . . . . . . . . . . . . . . 19		4. Status Code Definitions . . . . . . . . . . . . . . . . . . . 19
	4.1. 304 Not Modified . . . . . . . . . . . . . . . . . . . . . 19		4.1. 304 Not Modified . . . . . . . . . . . . . . . . . . . . . 19
	4.2. 412 Precondition Failed . . . . . . . . . . . . . . . . . 20		4.2. 412 Precondition Failed . . . . . . . . . . . . . . . . . 20
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
	5.1. Status Code Registration . . . . . . . . . . . . . . . . . 20		5.1. Status Code Registration . . . . . . . . . . . . . . . . . 20
	5.2. Header Field Registration . . . . . . . . . . . . . . . . 20		5.2. Header Field Registration . . . . . . . . . . . . . . . . 20
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 20		6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 21		8.1. Normative References . . . . . . . . . . . . . . . . . . . 21
	8.2. Informative References . . . . . . . . . . . . . . . . . . 21		8.2. Informative References . . . . . . . . . . . . . . . . . . 22
	Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 22		Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 22
	Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 22		Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 23
	Appendix C. Change Log (to be removed by RFC Editor before		Appendix C. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 23		publication) . . . . . . . . . . . . . . . . . . . . 23
	C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 23		C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 23
	C.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 23		C.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 23
	C.3. Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 23		C.3. Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 24
	C.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 23		C.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 24
	C.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 24		C.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 24
	C.6. Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 24		C.6. Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 24
	C.7. Since draft-ietf-httpbis-p4-conditional-05 . . . . . . . . 24		C.7. Since draft-ietf-httpbis-p4-conditional-05 . . . . . . . . 25
	C.8. Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 24		C.8. Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 25
	C.9. Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 24		C.9. Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 25
	C.10. Since draft-ietf-httpbis-p4-conditional-08 . . . . . . . . 25		C.10. Since draft-ietf-httpbis-p4-conditional-08 . . . . . . . . 25
	C.11. Since draft-ietf-httpbis-p4-conditional-09 . . . . . . . . 25		C.11. Since draft-ietf-httpbis-p4-conditional-09 . . . . . . . . 25
	C.12. Since draft-ietf-httpbis-p4-conditional-10 . . . . . . . . 25		C.12. Since draft-ietf-httpbis-p4-conditional-10 . . . . . . . . 25
	C.13. Since draft-ietf-httpbis-p4-conditional-11 . . . . . . . . 25		C.13. Since draft-ietf-httpbis-p4-conditional-11 . . . . . . . . 26
	C.14. Since draft-ietf-httpbis-p4-conditional-12 . . . . . . . . 25		C.14. Since draft-ietf-httpbis-p4-conditional-12 . . . . . . . . 26
	C.15. Since draft-ietf-httpbis-p4-conditional-13 . . . . . . . . 25		C.15. Since draft-ietf-httpbis-p4-conditional-13 . . . . . . . . 26
	C.16. Since draft-ietf-httpbis-p4-conditional-14 . . . . . . . . 26		C.16. Since draft-ietf-httpbis-p4-conditional-14 . . . . . . . . 26
	C.17. Since draft-ietf-httpbis-p4-conditional-15 . . . . . . . . 26		C.17. Since draft-ietf-httpbis-p4-conditional-15 . . . . . . . . 26
	C.18. Since draft-ietf-httpbis-p4-conditional-16 . . . . . . . . 26		C.18. Since draft-ietf-httpbis-p4-conditional-16 . . . . . . . . 26
	Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26		C.19. Since draft-ietf-httpbis-p4-conditional-17 . . . . . . . . 27
			Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
	1. Introduction		1. Introduction
	This document defines the HTTP/1.1 conditional request mechanisms,		This document defines the HTTP/1.1 conditional request mechanisms,
	including both metadata for indicating/observing changes in resource		including both metadata for indicating/observing changes in resource
	representations and request header fields that specify preconditions		representations and request header fields that specify preconditions
	on that metadata be checked before performing the request method.		on that metadata be checked before performing the request method.
	Conditional GET requests are the most efficient mechanism for HTTP		Conditional GET requests are the most efficient mechanism for HTTP
	cache updates [Part6]. Conditionals can also be applied to state-		cache updates [Part6]. Conditionals can also be applied to state-
	changing methods, such as PUT and DELETE, to prevent the "lost		changing methods, such as PUT and DELETE, to prevent the "lost
	skipping to change at page 6, line 34		skipping to change at page 6, line 34
	The following core rules are included by reference, as defined in		The following core rules are included by reference, as defined in
	[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF		[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
	(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),		(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
	HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit		HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
	sequence of data), SP (space), and VCHAR (any visible US-ASCII		sequence of data), SP (space), and VCHAR (any visible US-ASCII
	character).		character).
	The ABNF rules below are defined in [Part1] and [Part2]:		The ABNF rules below are defined in [Part1] and [Part2]:
	OWS = <OWS, defined in [Part1], Section 1.2.2>		OWS = <OWS, defined in [Part1], Section 1.2.2>
	quoted-string = <quoted-string, defined in [Part1], Section 3.2.3>		obs-text = <obs-text, defined in [Part1], Section 3.2.3>
	HTTP-date = <HTTP-date, defined in [Part2], Section 8>		HTTP-date = <HTTP-date, defined in [Part2], Section 8>
	2. Validators		2. Validators
	This specification defines two forms of metadata that are commonly		This specification defines two forms of metadata that are commonly
	used to observe resource state and test for preconditions:		used to observe resource state and test for preconditions:
	modification dates and opaque entity tags. Additional metadata that		modification dates and opaque entity tags. Additional metadata that
	reflects resource state has been defined by various extensions of		reflects resource state has been defined by various extensions of
	HTTP, such as WebDAV [RFC4918], that are beyond the scope of this		HTTP, such as WebDAV [RFC4918], that are beyond the scope of this
	specification. A resource metadata value is referred to as a		specification. A resource metadata value is referred to as a
	skipping to change at page 10, line 47		skipping to change at page 10, line 47
	resource, regardless of whether those multiple representations are		resource, regardless of whether those multiple representations are
	due to resource state changes over time, content negotiation		due to resource state changes over time, content negotiation
	resulting in multiple representations being valid at the same time,		resulting in multiple representations being valid at the same time,
	or both. An entity-tag consists of an opaque quoted string, possibly		or both. An entity-tag consists of an opaque quoted string, possibly
	prefixed by a weakness indicator.		prefixed by a weakness indicator.
	ETag = entity-tag		ETag = entity-tag
	entity-tag = [ weak ] opaque-tag		entity-tag = [ weak ] opaque-tag
	weak = %x57.2F ; "W/", case-sensitive		weak = %x57.2F ; "W/", case-sensitive
	opaque-tag = quoted-string		opaque-tag = DQUOTE *etagc DQUOTE
			etagc = %x21 / %x23-7E / obs-text
			; VCHAR except double quotes, plus obs-text
			Note: Previously, opaque-tag was defined to be a quoted-string
			([RFC2616], Section 3.11), thus some recipients might perform
			backslash unescaping. Servers therefore ought to avoid backslash
			characters in entity tags.
	An entity-tag can be more reliable for validation than a modification		An entity-tag can be more reliable for validation than a modification
	date in situations where it is inconvenient to store modification		date in situations where it is inconvenient to store modification
	dates, where the one-second resolution of HTTP date values is not		dates, where the one-second resolution of HTTP date values is not
	sufficient, or where modification dates are not consistently		sufficient, or where modification dates are not consistently
	maintained.		maintained.
	Examples:		Examples:
	ETag: "xyzzy"		ETag: "xyzzy"
	skipping to change at page 21, line 16		skipping to change at page 21, line 35
	See Section 11 of [Part1].		See Section 11 of [Part1].
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,		and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,
	and Message Parsing", draft-ietf-httpbis-p1-messaging-17		and Message Parsing", draft-ietf-httpbis-p1-messaging-18
	(work in progress), October 2011.		(work in progress), January 2012.
	[Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	and J. Reschke, Ed., "HTTP/1.1, part 2: Message		and J. Reschke, Ed., "HTTP/1.1, part 2: Message
	Semantics", draft-ietf-httpbis-p2-semantics-17 (work in		Semantics", draft-ietf-httpbis-p2-semantics-18 (work in
	progress), October 2011.		progress), January 2012.
	[Part3] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part3] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload		and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload
	and Content Negotiation", draft-ietf-httpbis-p3-payload-17		and Content Negotiation", draft-ietf-httpbis-p3-payload-18
	(work in progress), October 2011.		(work in progress), January 2012.
	[Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and		and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
	Partial Responses", draft-ietf-httpbis-p5-range-17 (work		Partial Responses", draft-ietf-httpbis-p5-range-18 (work
	in progress), October 2011.		in progress), January 2012.
	[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part		Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part
	6: Caching", draft-ietf-httpbis-p6-cache-17 (work in		6: Caching", draft-ietf-httpbis-p6-cache-18 (work in
	progress), October 2011.		progress), January 2012.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax		[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234, January 2008.		Specifications: ABNF", STD 68, RFC 5234, January 2008.
	8.2. Informative References		8.2. Informative References
	[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,		[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
	skipping to change at page 22, line 18		skipping to change at page 22, line 37
	September 2004.		September 2004.
	[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed		[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
	Authoring and Versioning (WebDAV)", RFC 4918, June 2007.		Authoring and Versioning (WebDAV)", RFC 4918, June 2007.
	Appendix A. Changes from RFC 2616		Appendix A. Changes from RFC 2616
	Allow weak entity-tags in all requests except range requests		Allow weak entity-tags in all requests except range requests
	(Sections 2.1 and 3.2).		(Sections 2.1 and 3.2).
			Change ETag header field ABNF not to use quoted-string, thus avoiding
			escaping issues. (Section 2.3)
	Change ABNF productions for header fields to only define the field		Change ABNF productions for header fields to only define the field
	value. (Section 3)		value. (Section 3)
	Appendix B. Collected ABNF		Appendix B. Collected ABNF
	ETag = entity-tag		ETag = entity-tag
	HTTP-date = <HTTP-date, defined in [Part2], Section 8>		HTTP-date = <HTTP-date, defined in [Part2], Section 8>
	If-Match = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS		If-Match = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
	skipping to change at page 22, line 39		skipping to change at page 23, line 23
	If-Modified-Since = HTTP-date		If-Modified-Since = HTTP-date
	If-None-Match = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS		If-None-Match = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
	entity-tag ] ) )		entity-tag ] ) )
	If-Unmodified-Since = HTTP-date		If-Unmodified-Since = HTTP-date
	Last-Modified = HTTP-date		Last-Modified = HTTP-date
	OWS = <OWS, defined in [Part1], Section 1.2.2>		OWS = <OWS, defined in [Part1], Section 1.2.2>
	entity-tag = [ weak ] opaque-tag		entity-tag = [ weak ] opaque-tag
			etagc = "!" / %x23-7E ; '#'-'~'
			/ obs-text
	opaque-tag = quoted-string		obs-text = <obs-text, defined in [Part1], Section 3.2.3>
			opaque-tag = DQUOTE *etagc DQUOTE
	quoted-string = <quoted-string, defined in [Part1], Section 3.2.3>
	weak = %x57.2F ; W/		weak = %x57.2F ; W/
	ABNF diagnostics:		ABNF diagnostics:
	; ETag defined but not used		; ETag defined but not used
	; If-Match defined but not used		; If-Match defined but not used
	; If-Modified-Since defined but not used		; If-Modified-Since defined but not used
	; If-None-Match defined but not used		; If-None-Match defined but not used
	; If-Unmodified-Since defined but not used		; If-Unmodified-Since defined but not used
	; Last-Modified defined but not used		; Last-Modified defined but not used
	Appendix C. Change Log (to be removed by RFC Editor before publication)		Appendix C. Change Log (to be removed by RFC Editor before publication)
	skipping to change at page 26, line 27		skipping to change at page 27, line 5
	should be listed when dicussing contexts where L-M can be		should be listed when dicussing contexts where L-M can be
	considered strong"		considered strong"
	C.18. Since draft-ietf-httpbis-p4-conditional-16		C.18. Since draft-ietf-httpbis-p4-conditional-16
	Closed issues:		Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document		o <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document
	HTTP's error-handling philosophy"		HTTP's error-handling philosophy"
			C.19. Since draft-ietf-httpbis-p4-conditional-17
			Closed issues:
			o <http://tools.ietf.org/wg/httpbis/trac/ticket/306>: "does etag
			value really use quoted-string"
	Index		Index
	3		3
	304 Not Modified (status code) 19		304 Not Modified (status code) 19
	4		4
	412 Precondition Failed (status code) 20		412 Precondition Failed (status code) 20
	E		E
	ETag header field 10		ETag header field 10
	G		G
	Grammar		Grammar
	entity-tag 10		entity-tag 10
	ETag 10		ETag 10
			etagc 10
	If-Match 15		If-Match 15
	If-Modified-Since 17		If-Modified-Since 17
	If-None-Match 16		If-None-Match 16
	If-Unmodified-Since 18		If-Unmodified-Since 18
	Last-Modified 8		Last-Modified 8
	opaque-tag 10		opaque-tag 10
	weak 10		weak 10
	H		H
	Header Fields		Header Fields
	ETag 10		ETag 10
	If-Match 15		If-Match 15
	If-Modified-Since 17		If-Modified-Since 17
	If-None-Match 15		If-None-Match 16
	If-Unmodified-Since 18		If-Unmodified-Since 18
	Last-Modified 8		Last-Modified 8
	I		I
	If-Match header field 15		If-Match header field 15
	If-Modified-Since header field 17		If-Modified-Since header field 17
	If-None-Match header field 15		If-None-Match header field 16
	If-Unmodified-Since header field 18		If-Unmodified-Since header field 18
	L		L
	Last-Modified header field 8		Last-Modified header field 8
	M		M
	metadata 6		metadata 6
	S		S
	selected representation 5		selected representation 5
End of changes. 31 change blocks.
	38 lines changed or deleted		59 lines changed or added
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