draft-ietf-httpbis-p4-conditional-19.txt		draft-ietf-httpbis-p4-conditional-latest.txt
	HTTPbis Working Group R. Fielding, Ed.		HTTPbis Working Group R. Fielding, Ed.
	Internet-Draft Adobe		Internet-Draft Adobe
	Obsoletes: 2616 (if approved) Y. Lafon, Ed.		Obsoletes: 2616 (if approved) Y. Lafon, Ed.
	Intended status: Standards Track W3C		Intended status: Standards Track W3C
	Expires: September 13, 2012 J. Reschke, Ed.		Expires: November 20, 2012 J. Reschke, Ed.
	greenbytes		greenbytes
	March 12, 2012		May 19, 2012
	HTTP/1.1, part 4: Conditional Requests		HTTP/1.1, part 4: Conditional Requests
	draft-ietf-httpbis-p4-conditional-19		draft-ietf-httpbis-p4-conditional-latest
	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 37		skipping to change at page 1, line 37
	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.20.		The changes in this draft are summarized in Appendix C.1.
	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 September 13, 2012.		This Internet-Draft will expire on November 20, 2012.
	Copyright Notice		Copyright Notice
	Copyright (c) 2012 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
	skipping to change at page 3, line 28		skipping to change at page 3, line 43
	5.2. Header Field Registration . . . . . . . . . . . . . . . . 19		5.2. Header Field Registration . . . . . . . . . . . . . . . . 19
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 20		6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 20		8.1. Normative References . . . . . . . . . . . . . . . . . . . 20
	8.2. Informative References . . . . . . . . . . . . . . . . . . 21		8.2. Informative References . . . . . . . . . . . . . . . . . . 21
	Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 21		Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 21
	Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 22		Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 22
	Appendix C. Change Log (to be removed by RFC Editor before		Appendix C. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 22		publication) . . . . . . . . . . . . . . . . . . . . 22
	C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 22		C.1. Since draft-ietf-httpbis-p4-conditional-19 . . . . . . . . 22
	C.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 22		Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
	C.3. Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 23
	C.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 23
	C.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 23
	C.6. Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 23
	C.7. Since draft-ietf-httpbis-p4-conditional-05 . . . . . . . . 24
	C.8. Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 24
	C.9. Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 24
	C.10. Since draft-ietf-httpbis-p4-conditional-08 . . . . . . . . 24
	C.11. Since draft-ietf-httpbis-p4-conditional-09 . . . . . . . . 24
	C.12. Since draft-ietf-httpbis-p4-conditional-10 . . . . . . . . 24
	C.13. Since draft-ietf-httpbis-p4-conditional-11 . . . . . . . . 25
	C.14. Since draft-ietf-httpbis-p4-conditional-12 . . . . . . . . 25
	C.15. Since draft-ietf-httpbis-p4-conditional-13 . . . . . . . . 25
	C.16. Since draft-ietf-httpbis-p4-conditional-14 . . . . . . . . 25
	C.17. Since draft-ietf-httpbis-p4-conditional-15 . . . . . . . . 25
	C.18. Since draft-ietf-httpbis-p4-conditional-16 . . . . . . . . 25
	C.19. Since draft-ietf-httpbis-p4-conditional-17 . . . . . . . . 26
	C.20. Since draft-ietf-httpbis-p4-conditional-18 . . . . . . . . 26
	Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
	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 5, line 35		skipping to change at page 5, line 35
	[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 3.2.1>		OWS = <OWS, defined in [Part1], Section 3.2.1>
	obs-text = <obs-text, defined in [Part1], Section 3.2.4>		obs-text = <obs-text, defined in [Part1], Section 3.2.4>
	HTTP-date = <HTTP-date, defined in [Part2], Section 8>		HTTP-date = <HTTP-date, defined in [Part2], Section 5.1>
	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
	"validator" when it is used within a precondition.		"validator" when it is used within a precondition.
	skipping to change at page 11, line 33		skipping to change at page 11, line 33
	| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |		| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
	+--------+--------+-------------------+-----------------+		+--------+--------+-------------------+-----------------+
	| W/"1" | W/"1" | no match | match |		| W/"1" | W/"1" | no match | match |
	| W/"1" | W/"2" | no match | no match |		| W/"1" | W/"2" | no match | no match |
	| W/"1" | "1" | no match | match |		| W/"1" | "1" | no match | match |
	| "1" | "1" | match | match |		| "1" | "1" | match | match |
	+--------+--------+-------------------+-----------------+		+--------+--------+-------------------+-----------------+
	2.3.3. Example: Entity-tags varying on Content-Negotiated Resources		2.3.3. Example: Entity-tags varying on Content-Negotiated Resources
	Consider a resource that is subject to content negotiation (Section 5		Consider a resource that is subject to content negotiation (Section 8
	of [Part3]), and where the representations returned upon a GET		of [Part2]), and where the representations returned upon a GET
	request vary based on the Accept-Encoding request header field		request vary based on the Accept-Encoding request header field
	(Section 6.3 of [Part3]):		(Section 9.3 of [Part2]):
	>> Request:		>> Request:
	GET /index HTTP/1.1		GET /index HTTP/1.1
	Host: www.example.com		Host: www.example.com
	Accept-Encoding: gzip		Accept-Encoding: gzip
	In this case, the response might or might not use the gzip content		In this case, the response might or might not use the gzip content
	coding. If it does not, the response might look like:		coding. If it does not, the response might look like:
	skipping to change at page 12, line 36		skipping to change at page 12, line 36
	Date: Thu, 26 Mar 2010 00:05:00 GMT		Date: Thu, 26 Mar 2010 00:05:00 GMT
	ETag: "123-b"		ETag: "123-b"
	Content-Length: 43		Content-Length: 43
	Vary: Accept-Encoding		Vary: Accept-Encoding
	Content-Type: text/plain		Content-Type: text/plain
	Content-Encoding: gzip		Content-Encoding: gzip
	...binary data...		...binary data...
	Note: Content codings are a property of the representation, so		Note: Content codings are a property of the representation, so
	therefore an entity-tag of an encoded representation must be		therefore an entity-tag of an encoded representation has to be
	distinct from an unencoded representation to prevent conflicts		distinct from an unencoded representation to prevent conflicts
	during cache updates and range requests. In contrast, transfer		during cache updates and range requests. In contrast, transfer
	codings (Section 4 of [Part1]) apply only during message transfer		codings (Section 4 of [Part1]) apply only during message transfer
	and do not require distinct entity-tags.		and do not require distinct entity-tags.
	2.4. Rules for When to Use Entity-tags and Last-Modified Dates		2.4. Rules for When to Use Entity-tags and Last-Modified Dates
	We adopt a set of rules and recommendations for origin servers,		We adopt a set of rules and recommendations for origin servers,
	clients, and caches regarding when various validator types ought to		clients, and caches regarding when various validator types ought to
	be used, and for what purposes.		be used, and for what purposes.
	skipping to change at page 18, line 39		skipping to change at page 18, line 39
	received and would have resulted in a 200 (OK) response if it were		received and would have resulted in a 200 (OK) response if it were
	not for the fact that the condition has evaluated to false. In other		not for the fact that the condition has evaluated to false. In other
	words, there is no need for the server to transfer a representation		words, there is no need for the server to transfer a representation
	of the target resource because the client's request indicates that it		of the target resource because the client's request indicates that it
	already has a valid representation, as indicated by the 304 response		already has a valid representation, as indicated by the 304 response
	header fields, and is therefore redirecting the client to make use of		header fields, and is therefore redirecting the client to make use of
	that stored representation as if it were the payload of a 200		that stored representation as if it were the payload of a 200
	response. The 304 response MUST NOT contain a message-body, and thus		response. The 304 response MUST NOT contain a message-body, and thus
	is always terminated by the first empty line after the header fields.		is always terminated by the first empty line after the header fields.
	A 304 response MUST include a Date header field (Section 10.2 of		A 304 response MUST include a Date header field (Section 9.10 of
	[Part2]) unless the origin server does not have a clock that can		[Part2]) unless the origin server does not have a clock that can
	provide a reasonable approximation of the current time. If a 200		provide a reasonable approximation of the current time. If a 200
	response to the same request would have included any of the header		response to the same request would have included any of the header
	fields Cache-Control, Content-Location, ETag, Expires, or Vary, then		fields Cache-Control, Content-Location, ETag, Expires, or Vary, then
	those same header fields MUST be sent in a 304 response.		those same header fields MUST be sent in a 304 response.
	Since the goal of a 304 response is to minimize information transfer		Since the goal of a 304 response is to minimize information transfer
	when the recipient already has one or more cached representations,		when the recipient already has one or more cached representations,
	the response SHOULD NOT include representation metadata other than		the response SHOULD NOT include representation metadata other than
	the above listed fields unless said metadata exists for the purpose		the above listed fields unless said metadata exists for the purpose
	skipping to change at page 20, line 34		skipping to change at page 20, line 34
	7. Acknowledgments		7. Acknowledgments
	See Section 9 of [Part1].		See Section 9 of [Part1].
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[Part1] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,		[Part1] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
	"HTTP/1.1, part 1: URIs, Connections, and Message		"HTTP/1.1, part 1: URIs, Connections, and Message
	Parsing", draft-ietf-httpbis-p1-messaging-19 (work in		Parsing", draft-ietf-httpbis-p1-messaging-latest (work in
	progress), March 2012.		progress), May 2012.
	[Part2] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,		[Part2] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
	"HTTP/1.1, part 2: Message Semantics",		"HTTP/1.1, part 2: Message Semantics",
	draft-ietf-httpbis-p2-semantics-19 (work in progress),		draft-ietf-httpbis-p2-semantics-latest (work in progress),
	March 2012.		May 2012.
	[Part3] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
	"HTTP/1.1, part 3: Message Payload and Content
	Negotiation", draft-ietf-httpbis-p3-payload-19 (work in
	progress), March 2012.
	[Part5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,		[Part5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
	"HTTP/1.1, part 5: Range Requests and Partial Responses",		"HTTP/1.1, part 5: Range Requests and Partial Responses",
	draft-ietf-httpbis-p5-range-19 (work in progress),		draft-ietf-httpbis-p5-range-latest (work in progress),
	March 2012.		May 2012.
	[Part6] Fielding, R., Ed., Lafon, Y., Ed., Nottingham, M., Ed.,		[Part6] Fielding, R., Ed., Lafon, Y., Ed., Nottingham, M., Ed.,
	and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",		and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",
	draft-ietf-httpbis-p6-cache-19 (work in progress),		draft-ietf-httpbis-p6-cache-latest (work in progress),
	March 2012.		May 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 9		skipping to change at page 22, line 9
	Change ETag header field ABNF not to use quoted-string, thus avoiding		Change ETag header field ABNF not to use quoted-string, thus avoiding
	escaping issues. (Section 2.3)		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 6.1>
	If-Match = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS		If-Match = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
	entity-tag ] ) )		entity-tag ] ) )
	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
	skipping to change at page 22, line 42		skipping to change at page 22, line 42
	; 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)
	C.1. Since RFC 2616		Changes up to the first Working Group Last Call draft are summarized
			in <http://tools.ietf.org/html/
	Extracted relevant partitions from [RFC2616].		draft-ietf-httpbis-p4-conditional-19#appendix-C>.
	C.2. Since draft-ietf-httpbis-p4-conditional-00
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
	Informative references"
	Other changes:
	o Move definitions of 304 and 412 condition codes from Part2.
	C.3. Since draft-ietf-httpbis-p4-conditional-01
	Ongoing work on ABNF conversion
	(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
	o Add explicit references to BNF syntax and rules imported from
	other parts of the specification.
	C.4. Since draft-ietf-httpbis-p4-conditional-02
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/116>: "Weak ETags on
	non-GET requests"
	Ongoing work on IANA Message Header Field Registration
	(<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):
	o Reference RFC 3984, and update header field registrations for
	header fields defined in this document.
	C.5. Since draft-ietf-httpbis-p4-conditional-03
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/71>: "Examples for
	ETag matching"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/124>: "'entity
	value' undefined"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/126>: "bogus 2068
	Date header reference"
	C.6. Since draft-ietf-httpbis-p4-conditional-04
	Ongoing work on ABNF conversion
	(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
	o Use "/" instead of "|" for alternatives.
	o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
	whitespace ("OWS") and required whitespace ("RWS").
	o Rewrite ABNFs to spell out whitespace rules, factor out header
	field value format definitions.
	C.7. Since draft-ietf-httpbis-p4-conditional-05
	Final work on ABNF conversion
	(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
	o Add appendix containing collected and expanded ABNF, reorganize
	ABNF introduction.
	C.8. Since draft-ietf-httpbis-p4-conditional-06
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/153>: "case-
	sensitivity of etag weakness indicator"
	C.9. Since draft-ietf-httpbis-p4-conditional-07
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/116>: "Weak ETags on
	non-GET requests" (If-Match still was defined to require strong
	matching)
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/198>: "move IANA
	registrations for optional status codes"
	C.10. Since draft-ietf-httpbis-p4-conditional-08
	No significant changes.
	C.11. Since draft-ietf-httpbis-p4-conditional-09
	No significant changes.
	C.12. Since draft-ietf-httpbis-p4-conditional-10
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/69>: "Clarify
	'Requested Variant'"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
	entity / representation / variant terminology"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
	removing the 'changes from 2068' sections"
	C.13. Since draft-ietf-httpbis-p4-conditional-11
	None.
	C.14. Since draft-ietf-httpbis-p4-conditional-12
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/224>: "Header
	Classification"
	C.15. Since draft-ietf-httpbis-p4-conditional-13
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/89>: "If-* and
	entities"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/101>: "Definition of
	validator weakness"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
	ABNFs for header fields"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/269>: "ETags and
	Quotes"
	C.16. Since draft-ietf-httpbis-p4-conditional-14
	None.
	C.17. Since draft-ietf-httpbis-p4-conditional-15
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/304>: "If-Range
	should be listed when dicussing contexts where L-M can be
	considered strong"
	C.18. Since draft-ietf-httpbis-p4-conditional-16
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document
	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"
	C.20. Since draft-ietf-httpbis-p4-conditional-18
	Closed issues:		C.1. Since draft-ietf-httpbis-p4-conditional-19
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/345>: "Required		None yet.
	headers on 304 and 206"
	Index		Index
	3		3
	304 Not Modified (status code) 18		304 Not Modified (status code) 18
	4		4
	412 Precondition Failed (status code) 19		412 Precondition Failed (status code) 19
	E		E
End of changes. 19 change blocks.
	212 lines changed or deleted		27 lines changed or added
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