draft-ietf-httpbis-p4-conditional-15.txt		draft-ietf-httpbis-p4-conditional-16.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: January 12, 2012 J. Mogul		Expires: February 25, 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
	July 11, 2011		August 24, 2011
	HTTP/1.1, part 4: Conditional Requests		HTTP/1.1, part 4: Conditional Requests
	draft-ietf-httpbis-p4-conditional-15		draft-ietf-httpbis-p4-conditional-16
	Abstract		Abstract
	The Hypertext Transfer Protocol (HTTP) is an application-level		The Hypertext Transfer Protocol (HTTP) is an application-level
	protocol for distributed, collaborative, hypermedia 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. Part 4 defines		"HTTP/1.1" and, taken together, obsoletes RFC 2616.
	request header fields for indicating conditional requests and the
	rules for constructing responses to those requests.		Part 4 defines request header fields for indicating conditional
			requests and the rules for constructing responses to those requests.
	Editorial Note (To be removed by RFC Editor)		Editorial Note (To be removed by RFC Editor)
	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.16.		The changes in this draft are summarized in Appendix C.17.
	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 January 12, 2012.		This Internet-Draft will expire on February 25, 2012.
	Copyright Notice		Copyright Notice
	Copyright (c) 2011 IETF Trust and the persons identified as the		Copyright (c) 2011 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 5		skipping to change at page 3, line 5
	outside the IETF Standards Process, and derivative works of it may		outside the IETF Standards Process, and derivative works of it may
	not be created outside the IETF Standards Process, except to format		not be created outside the IETF Standards Process, except to format
	it for publication as an RFC or to translate it into languages other		it for publication as an RFC or to translate it into languages other
	than English.		than English.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
	1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5		1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5
	1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6		1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
	2. Resource State Metadata (Validators) . . . . . . . . . . . . . 6		2. Validators . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	2.1. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 6		2.1. Weak versus Strong . . . . . . . . . . . . . . . . . . . . 6
	2.1.1. Generation . . . . . . . . . . . . . . . . . . . . . . 6		2.2. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 8
	2.1.2. Comparison . . . . . . . . . . . . . . . . . . . . . . 7		2.2.1. Generation . . . . . . . . . . . . . . . . . . . . . . 8
	2.2. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 8		2.2.2. Comparison . . . . . . . . . . . . . . . . . . . . . . 9
	2.2.1. Generation . . . . . . . . . . . . . . . . . . . . . . 9		2.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
	2.2.2. Weak versus Strong . . . . . . . . . . . . . . . . . . 9		2.3.1. Generation . . . . . . . . . . . . . . . . . . . . . . 11
	2.2.3. Comparison . . . . . . . . . . . . . . . . . . . . . . 11		2.3.2. Comparison . . . . . . . . . . . . . . . . . . . . . . 11
	2.2.4. Rules for When to Use Entity-tags and		2.3.3. Example: Entity-tags varying on Content-Negotiated
	Last-Modified Dates . . . . . . . . . . . . . . . . . 11		Resources . . . . . . . . . . . . . . . . . . . . . . 12
	2.2.5. Example: Entity-tags varying on Content-Negotiated		2.4. Rules for When to Use Entity-tags and Last-Modified
	Resources . . . . . . . . . . . . . . . . . . . . . . 13		Dates . . . . . . . . . . . . . . . . . . . . . . . . . . 13
	3. Precondition Header Fields . . . . . . . . . . . . . . . . . . 14		3. Precondition Header Fields . . . . . . . . . . . . . . . . . . 14
	3.1. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 14		3.1. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 14
	3.2. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 15		3.2. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 15
	3.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 16		3.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 17
	3.4. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 18		3.4. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 18
	3.5. If-Range . . . . . . . . . . . . . . . . . . . . . . . . . 18		3.5. If-Range . . . . . . . . . . . . . . . . . . . . . . . . . 19
	4. Status Code Definitions . . . . . . . . . . . . . . . . . . . 18		4. Status Code Definitions . . . . . . . . . . . . . . . . . . . 19
	4.1. 304 Not Modified . . . . . . . . . . . . . . . . . . . . . 18		4.1. 304 Not Modified . . . . . . . . . . . . . . . . . . . . . 19
	4.2. 412 Precondition Failed . . . . . . . . . . . . . . . . . 19		4.2. 412 Precondition Failed . . . . . . . . . . . . . . . . . 20
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
	5.1. Status Code Registration . . . . . . . . . . . . . . . . . 19		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 . . . . . . . . . . . . . . . . . . . 20
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 20		8.1. Normative References . . . . . . . . . . . . . . . . . . . 21
	8.2. Informative References . . . . . . . . . . . . . . . . . . 21		8.2. Informative References . . . . . . . . . . . . . . . . . . 21
	Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 21		Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 22
	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) . . . . . . . . . . . . . . . . . . . . 23
	C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 22		C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 23
	C.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 22		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 . . . . . . . . 23
	C.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 23		C.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 23
	C.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 23		C.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 23
	C.6. Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 23		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 . . . . . . . . 24
	C.8. Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 24		C.8. Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 24
	C.9. Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 24		C.9. Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 24
	C.10. Since draft-ietf-httpbis-p4-conditional-08 . . . . . . . . 24		C.10. Since draft-ietf-httpbis-p4-conditional-08 . . . . . . . . 24
	C.11. Since draft-ietf-httpbis-p4-conditional-09 . . . . . . . . 24		C.11. Since draft-ietf-httpbis-p4-conditional-09 . . . . . . . . 25
	C.12. Since draft-ietf-httpbis-p4-conditional-10 . . . . . . . . 24		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 . . . . . . . . 25
	C.14. Since draft-ietf-httpbis-p4-conditional-12 . . . . . . . . 25		C.14. Since draft-ietf-httpbis-p4-conditional-12 . . . . . . . . 25
	C.15. Since draft-ietf-httpbis-p4-conditional-13 . . . . . . . . 25		C.15. Since draft-ietf-httpbis-p4-conditional-13 . . . . . . . . 25
	C.16. Since draft-ietf-httpbis-p4-conditional-14 . . . . . . . . 25		C.16. Since draft-ietf-httpbis-p4-conditional-14 . . . . . . . . 26
	Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25		C.17. Since draft-ietf-httpbis-p4-conditional-15 . . . . . . . . 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 response metadata that can be used to indicate or		including both metadata for indicating/observing changes in resource
	observe changes to resource state and request header fields that		representations and request header fields that specify preconditions
	specify preconditions to be checked before performing the action		on that metadata be checked before performing the request method.
	given by the request method. Conditional GET requests are the most		Conditional GET requests are the most efficient mechanism for HTTP
	efficient mechanism for HTTP cache updates [Part6]. Conditionals can		cache updates [Part6]. Conditionals can also be applied to state-
	also be applied to state-changing methods, such as PUT and DELETE, to		changing methods, such as PUT and DELETE, to prevent the "lost
	prevent the "lost update" problem: one client accidentally		update" problem: one client accidentally overwriting the work of
	overwriting the work of another client that has been acting in		another client that has been acting in parallel.
	parallel.
	Conditional request preconditions are based on the state of the		Conditional request preconditions are based on the state of the
	target resource as a whole (its current value set) or the state as		target resource as a whole (its current value set) or the state as
	observed in a previously obtained representation (one value in that		observed in a previously obtained representation (one value in that
	set). A resource might have multiple current representations, each		set). A resource might have multiple current representations, each
	with its own observable state. The conditional request mechanisms		with its own observable state. The conditional request mechanisms
	assume that the mapping of requests to corresponding representations		assume that the mapping of requests to corresponding representations
	will be consistent over time if the server intends to take advantage		will be consistent over time if the server intends to take advantage
	of conditionals. Regardless, if the mapping is inconsistent and the		of conditionals. Regardless, if the mapping is inconsistent and the
	server is unable to select the appropriate representation, then no		server is unable to select the appropriate representation, then no
	skipping to change at page 6, line 19		skipping to change at page 6, line 19
	rule). Appendix B shows the collected ABNF, with the list rule		rule). Appendix B shows the collected ABNF, with the list rule
	expanded.		expanded.
	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), VCHAR (any visible USASCII character),		sequence of data), SP (space), VCHAR (any visible USASCII character),
	and WSP (whitespace).		and WSP (whitespace).
	The ABNF rules below are defined in other parts:		The ABNF rules below are defined in [Part1]:
	quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
	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>
	HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>		HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
	2. Resource State Metadata (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.
	2.1. Last-Modified		2.1. Weak versus Strong
			Validators come in two flavors: strong or weak. Weak validators are
			easy to generate but are far less useful for comparisons. Strong
			validators are ideal for comparisons but can be very difficult (and
			occasionally impossible) to generate efficiently. Rather than impose
			that all forms of resource adhere to the same strength of validator,
			HTTP exposes the type of validator in use and imposes restrictions on
			when weak validators can be used as preconditions.
			A "strong validator" is a representation metadata value that MUST be
			changed to a new, previously unused or guaranteed unique, value
			whenever a change occurs to the representation data such that a
			change would be observable in the payload body of a 200 response to
			GET. A strong validator MAY be changed for other reasons, such as
			when a semantically significant part of the representation metadata
			is changed (e.g., Content-Type), but it is in the best interests of
			the origin server to only change the value when it is necessary to
			invalidate the stored responses held by remote caches and authoring
			tools. A strong validator MUST be unique across all representations
			of a given resource, such that no two representations of that
			resource share the same validator unless their payload body would be
			identical.
			Cache entries might persist for arbitrarily long periods, regardless
			of expiration times. Thus, a cache might attempt to validate an
			entry using a validator that it obtained in the distant past. A
			strong validator MUST be unique across all versions of all
			representations associated with a particular resource over time.
			However, there is no implication of uniqueness across representations
			of different resources (i.e., the same strong validator might be in
			use for representations of multiple resources at the same time and
			does not imply that those representations are equivalent).
			There are a variety of strong validators used in practice. The best
			are based on strict revision control, wherein each change to a
			representation always results in a unique node name and revision
			identifier being assigned before the representation is made
			accessible to GET. A cryptographic hash function applied to the
			representation data is also sufficient if the data is available prior
			to the response header fields being sent and the digest does not need
			to be recalculated every time a validation request is received.
			However, if a resource has distinct representations that differ only
			in their metadata, such as might occur with content negotiation over
			media types that happen to share the same data format, then a server
			SHOULD incorporate additional information in the validator to
			distinguish those representations and avoid confusing cache behavior.
			In contrast, a "weak validator" is a representation metadata value
			that might not be changed for every change to the representation
			data. This weakness might be due to limitations in how the value is
			calculated, such as clock resolution or an inability to ensure
			uniqueness for all possible representations of the resource, or due
			to a desire by the resource owner to group representations by some
			self-determined set of equivalency rather than unique sequences of
			data. A weak entity-tag SHOULD change whenever the origin server
			considers prior representations to be unacceptable as a substitute
			for the current representation. In other words, a weak entity-tag
			SHOULD change whenever the origin server wants caches to invalidate
			old responses.
			For example, the representation of a weather report that changes in
			content every second, based on dynamic measurements, might be grouped
			into sets of equivalent representations (from the origin server's
			perspective) with the same weak validator in order to allow cached
			representations to be valid for a reasonable period of time (perhaps
			adjusted dynamically based on server load or weather quality).
			Likewise, a representation's modification time, if defined with only
			one-second resolution, might be a weak validator if it is possible
			for the representation to be modified twice during a single second
			and retrieved between those modifications.
			A "use" of a validator occurs when either a client generates a
			request and includes the validator in a precondition or when a server
			compares two validators. Weak validators are only usable in contexts
			that do not depend on exact equality of a representation's payload
			body. Strong validators are usable and preferred for all conditional
			requests, including cache validation, partial content ranges, and
			"lost update" avoidance.
			2.2. Last-Modified
	The "Last-Modified" header field indicates the date and time at which		The "Last-Modified" header field indicates the date and time at which
	the origin server believes the selected representation was last		the origin server believes the selected representation was last
	modified.		modified.
	Last-Modified = HTTP-date		Last-Modified = HTTP-date
	An example of its use is		An example of its use is
	Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT		Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
	2.1.1. Generation		2.2.1. Generation
	Origin servers SHOULD send Last-Modified for any selected		Origin servers SHOULD send Last-Modified for any selected
	representation for which a last modification date can be reasonably		representation for which a last modification date can be reasonably
	and consistently determined, since its use in conditional requests		and consistently determined, since its use in conditional requests
	and evaluating cache freshness ([Part6]) results in a substantial		and evaluating cache freshness ([Part6]) results in a substantial
	reduction of HTTP traffic on the Internet and can be a significant		reduction of HTTP traffic on the Internet and can be a significant
	factor in improving service scalability and reliability.		factor in improving service scalability and reliability.
	A representation is typically the sum of many parts behind the		A representation is typically the sum of many parts behind the
	resource interface. The last-modified time would usually be the most		resource interface. The last-modified time would usually be the most
	skipping to change at page 7, line 31		skipping to change at page 9, line 15
	response is generated.		response is generated.
	An origin server with a clock MUST NOT send a Last-Modified date that		An origin server with a clock MUST NOT send a Last-Modified date that
	is later than the server's time of message origination (Date). If		is later than the server's time of message origination (Date). If
	the last modification time is derived from implementation-specific		the last modification time is derived from implementation-specific
	metadata that evaluates to some time in the future, according to the		metadata that evaluates to some time in the future, according to the
	origin server's clock, then the origin server MUST replace that value		origin server's clock, then the origin server MUST replace that value
	with the message origination date. This prevents a future		with the message origination date. This prevents a future
	modification date from having an adverse impact on cache validation.		modification date from having an adverse impact on cache validation.
	2.1.2. Comparison		2.2.2. Comparison
	A Last-Modified time, when used as a validator in a request, is		A Last-Modified time, when used as a validator in a request, is
	implicitly weak unless it is possible to deduce that it is strong,		implicitly weak unless it is possible to deduce that it is strong,
	using the following rules:		using the following rules:
	o The validator is being compared by an origin server to the actual		o The validator is being compared by an origin server to the actual
	current validator for the representation and,		current validator for the representation and,
	o That origin server reliably knows that the associated		o That origin server reliably knows that the associated
	representation did not change twice during the second covered by		representation did not change twice during the second covered by
	the presented validator.		the presented validator.
	or		or
	o The validator is about to be used by a client in an If-Modified-		o The validator is about to be used by a client in an If-Modified-
	Since or If-Unmodified-Since header field, because the client has		Since, If-Unmodified-Since header field, because the client has a
	a cache entry for the associated representation, and		cache entry, or If-Range for the associated representation, and
	o That cache entry includes a Date value, which gives the time when		o That cache entry includes a Date value, which gives the time when
	the origin server sent the original response, and		the origin server sent the original response, and
	o The presented Last-Modified time is at least 60 seconds before the		o The presented Last-Modified time is at least 60 seconds before the
	Date value.		Date value.
	or		or
	o The validator is being compared by an intermediate cache to the		o The validator is being compared by an intermediate cache to the
	skipping to change at page 8, line 29		skipping to change at page 10, line 13
	This method relies on the fact that if two different responses were		This method relies on the fact that if two different responses were
	sent by the origin server during the same second, but both had the		sent by the origin server during the same second, but both had the
	same Last-Modified time, then at least one of those responses would		same Last-Modified time, then at least one of those responses would
	have a Date value equal to its Last-Modified time. The arbitrary 60-		have a Date value equal to its Last-Modified time. The arbitrary 60-
	second limit guards against the possibility that the Date and Last-		second limit guards against the possibility that the Date and Last-
	Modified values are generated from different clocks, or at somewhat		Modified values are generated from different clocks, or at somewhat
	different times during the preparation of the response. An		different times during the preparation of the response. An
	implementation MAY use a value larger than 60 seconds, if it is		implementation MAY use a value larger than 60 seconds, if it is
	believed that 60 seconds is too short.		believed that 60 seconds is too short.
	2.2. ETag		2.3. ETag
	The ETag header field provides the current entity-tag for the		The ETag header field provides the current entity-tag for the
	selected representation. An entity-tag is an opaque validator for		selected representation. An entity-tag is an opaque validator for
	differentiating between multiple representations of the same		differentiating between multiple representations of the same
	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.
	skipping to change at page 9, line 11		skipping to change at page 10, line 42
	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"
	ETag: W/"xyzzy"		ETag: W/"xyzzy"
	ETag: ""		ETag: ""
	2.2.1. Generation		An entity-tag can be either a weak or strong validator, with strong
			being the default. If an origin server provides an entity-tag for a
			representation and the generation of that entity-tag does not satisfy
			the requirements for a strong validator (Section 2.1), then that
			entity-tag MUST be marked as weak by prefixing its opaque value with
			"W/" (case-sensitive).
			2.3.1. Generation
	The principle behind entity-tags is that only the service author		The principle behind entity-tags is that only the service author
	knows the implementation of a resource well enough to select the most		knows the implementation of a resource well enough to select the most
	accurate and efficient validation mechanism for that resource, and		accurate and efficient validation mechanism for that resource, and
	that any such mechanism can be mapped to a simple sequence of octets		that any such mechanism can be mapped to a simple sequence of octets
	for easy comparison. Since the value is opaque, there is no need for		for easy comparison. Since the value is opaque, there is no need for
	the client to be aware of how each entity-tag is constructed.		the client to be aware of how each entity-tag is constructed.
	For example, a resource that has implementation-specific versioning		For example, a resource that has implementation-specific versioning
	applied to all changes might use an internal revision number, perhaps		applied to all changes might use an internal revision number, perhaps
	skipping to change at page 9, line 35		skipping to change at page 11, line 29
	combination of various filesystem attributes, or a modification		combination of various filesystem attributes, or a modification
	timestamp that has sub-second resolution.		timestamp that has sub-second resolution.
	Origin servers SHOULD send ETag for any selected representation for		Origin servers SHOULD send ETag for any selected representation for
	which detection of changes can be reasonably and consistently		which detection of changes can be reasonably and consistently
	determined, since the entity-tag's use in conditional requests and		determined, since the entity-tag's use in conditional requests and
	evaluating cache freshness ([Part6]) can result in a substantial		evaluating cache freshness ([Part6]) can result in a substantial
	reduction of HTTP network traffic and can be a significant factor in		reduction of HTTP network traffic and can be a significant factor in
	improving service scalability and reliability.		improving service scalability and reliability.
	2.2.2. Weak versus Strong		2.3.2. Comparison
	Since both origin servers and caches will compare two validators to
	decide if they indicate the same or different representations, one
	normally would expect that if the representation (including both
	representation header fields and representation body) changes in any
	way, then the associated validator would change as well. If this is
	true, then we call that validator a "strong validator". One example
	of a strong validator is an integer that is incremented in stable
	storage every time a representation is changed.
	However, there might be cases when a server prefers to change the
	validator only when it desires cached representations to be
	invalidated. For example, the representation of a weather report
	that changes in content every second, based on dynamic measurements,
	might be grouped into sets of equivalent representations (from the
	origin server's perspective) in order to allow cached representations
	to be valid for a reasonable period of time (perhaps adjusted
	dynamically based on server load or weather quality). A validator
	that does not always change when the representation changes is a
	"weak validator".
	One can think of a strong validator as part of an identifier for a
	specific representation, whereas a weak validator is part of an
	identifier for a set of equivalent representations (where this notion
	of equivalence is entirely governed by the origin server and beyond
	the scope of this specification).
	An entity-tag is normally a strong validator, but the protocol
	provides a mechanism to tag an entity-tag as "weak".
	A representation's modification time, if defined with only one-
	second resolution, could be a weak validator, since it is possible
	that the representation might be modified twice during a single
	second.
	Support for weak validators is optional. However, weak validators
	allow for more efficient caching of equivalent objects; for
	example, a hit counter on a site is probably good enough if it is
	updated every few days or weeks, and any value during that period
	is likely "good enough" to be equivalent.
	A strong entity-tag MUST change whenever the associated
	representation changes in any way. A weak entity-tag SHOULD change
	whenever the origin server considers prior representations to be
	unacceptable as a substitute for the current representation. In
	other words, a weak entity tag SHOULD change whenever the origin
	server wants caches to invalidate old responses.
	A "strong entity-tag" MAY be shared by two representations of a
	resource only if they are equivalent by octet equality.
	A "weak entity-tag", indicated by the "W/" prefix, MAY be shared by
	two representations of a resource. A weak entity-tag can only be
	used for weak comparison.
	Cache entries might persist for arbitrarily long periods, regardless
	of expiration times. Thus, a cache might attempt to validate an
	entry using a validator that it obtained in the distant past. A
	strong entity-tag MUST be unique across all versions of all
	representations associated with a particular resource over time.
	However, there is no implication of uniqueness across entity-tags of
	different resources (i.e., the same entity-tag value might be in use
	for representations of multiple resources at the same time and does
	not imply that those representations are equivalent).
	2.2.3. Comparison
	There are two entity-tag comparison functions, depending on whether		There are two entity-tag comparison functions, depending on whether
	the comparison context allows the use of weak validators or not:		the comparison context allows the use of weak validators or not:
	o The strong comparison function: in order to be considered equal,		o The strong comparison function: in order to be considered equal,
	both opaque-tags MUST be identical character-by-character, and		both opaque-tags MUST be identical character-by-character, and
	both MUST NOT be weak.		both MUST NOT be weak.
	o The weak comparison function: in order to be considered equal,		o The weak comparison function: in order to be considered equal,
	both opaque-tags MUST be identical character-by-character, but		both opaque-tags MUST be identical character-by-character, but
	either or both of them MAY be tagged as "weak" without affecting		either or both of them MAY be tagged as "weak" without affecting
	the result.		the result.
	A "use" of a validator is either when a client generates a request
	and includes the validator in a precondition, or when a server
	compares two validators.
	Strong validators are usable in any context. Weak validators are
	only usable in contexts that do not depend on exact equality of a
	representation. For example, either kind is usable for a normal
	conditional GET.
	The example below shows the results for a set of entity-tag pairs,		The example below shows the results for a set of entity-tag pairs,
	and both the weak and strong comparison function results:		and both the weak and strong comparison function results:
	+--------+--------+-------------------+-----------------+		+--------+--------+-------------------+-----------------+
	| 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 |
	+--------+--------+-------------------+-----------------+		+--------+--------+-------------------+-----------------+
	An entity-tag is strong unless it is explicitly tagged as weak.		2.3.3. Example: Entity-tags varying on Content-Negotiated Resources
	2.2.4. Rules for When to Use Entity-tags and Last-Modified Dates		Consider a resource that is subject to content negotiation (Section 5
			of [Part3]), and where the representations returned upon a GET
			request vary based on the Accept-Encoding request header field
			(Section 6.3 of [Part3]):
			>> Request:
			GET /index HTTP/1.1
			Host: www.example.com
			Accept-Encoding: gzip
			In this case, the response might or might not use the gzip content
			coding. If it does not, the response might look like:
			>> Response:
			HTTP/1.1 200 OK
			Date: Thu, 26 Mar 2010 00:05:00 GMT
			ETag: "123-a"
			Content-Length: 70
			Vary: Accept-Encoding
			Content-Type: text/plain
			Hello World!
			Hello World!
			Hello World!
			Hello World!
			Hello World!
			An alternative representation that does use gzip content coding would
			be:
			>> Response:
			HTTP/1.1 200 OK
			Date: Thu, 26 Mar 2010 00:05:00 GMT
			ETag: "123-b"
			Content-Length: 43
			Vary: Accept-Encoding
			Content-Type: text/plain
			Content-Encoding: gzip
			...binary data...
			Note: Content codings are a property of the representation, so
			therefore an entity-tag of an encoded representation must be
			distinct from an unencoded representation to prevent conflicts
			during cache updates and range requests. In contrast, transfer
			codings (Section 6.2 of [Part1]) apply only during message
			transfer and do not require distinct entity-tags.
			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.
	HTTP/1.1 origin servers:		HTTP/1.1 origin servers:
	o SHOULD send an entity-tag validator unless it is not feasible to		o SHOULD send an entity-tag validator unless it is not feasible to
	generate one.		generate one.
	skipping to change at page 13, line 13		skipping to change at page 14, line 43
	conservative assumptions about the validators they receive.		conservative assumptions about the validators they receive.
	HTTP/1.0 clients and caches might ignore entity-tags. Generally,		HTTP/1.0 clients and caches might ignore entity-tags. Generally,
	last-modified values received or used by these systems will		last-modified values received or used by these systems will
	support transparent and efficient caching, and so HTTP/1.1 origin		support transparent and efficient caching, and so HTTP/1.1 origin
	servers should provide Last-Modified values. In those rare cases		servers should provide Last-Modified values. In those rare cases
	where the use of a Last-Modified value as a validator by an		where the use of a Last-Modified value as a validator by an
	HTTP/1.0 system could result in a serious problem, then HTTP/1.1		HTTP/1.0 system could result in a serious problem, then HTTP/1.1
	origin servers should not provide one.		origin servers should not provide one.
	2.2.5. Example: Entity-tags varying on Content-Negotiated Resources
	Consider a resource that is subject to content negotiation (Section 5
	of [Part3]), and where the representations returned upon a GET
	request vary based on the Accept-Encoding request header field
	(Section 6.3 of [Part3]):
	>> Request:
	GET /index HTTP/1.1
	Host: www.example.com
	Accept-Encoding: gzip
	In this case, the response might or might not use the gzip content
	coding. If it does not, the response might look like:
	>> Response:
	HTTP/1.1 200 OK
	Date: Thu, 26 Mar 2010 00:05:00 GMT
	ETag: "123-a"
	Content-Length: 70
	Vary: Accept-Encoding
	Content-Type: text/plain
	Hello World!
	Hello World!
	Hello World!
	Hello World!
	Hello World!
	An alternative representation that does use gzip content coding would
	be:
	>> Response:
	HTTP/1.1 200 OK
	Date: Thu, 26 Mar 2010 00:05:00 GMT
	ETag: "123-b"
	Content-Length: 43
	Vary: Accept-Encoding
	Content-Type: text/plain
	Content-Encoding: gzip
	...binary data...
	Note: Content codings are a property of the representation, so
	therefore an entity-tag of an encoded representation must be
	distinct from an unencoded representation to prevent conflicts
	during cache updates and range requests. In contrast, transfer
	codings (Section 6.2 of [Part1]) apply only during message
	transfer and do not require distinct entity-tags.
	3. Precondition Header Fields		3. Precondition Header Fields
	This section defines the syntax and semantics of HTTP/1.1 header		This section defines the syntax and semantics of HTTP/1.1 header
	fields for applying preconditions on requests.		fields for applying preconditions on requests.
	3.1. If-Match		3.1. If-Match
	The "If-Match" header field MAY be used to make a request method		The "If-Match" header field MAY be used to make a request method
	conditional on the current existence or value of an entity-tag for		conditional on the current existence or value of an entity-tag for
	one or more representations of the target resource. If-Match is		one or more representations of the target resource. If-Match is
	generally useful for resource update requests, such as PUT requests,		generally useful for resource update requests, such as PUT requests,
	as a means for protecting against accidental overwrites when multiple		as a means for protecting against accidental overwrites when multiple
	clients are acting in parallel on the same resource (i.e., the "lost		clients are acting in parallel on the same resource (i.e., the "lost
	update" problem). An If-Match field-value of "*" places the		update" problem). An If-Match field-value of "*" places the
	precondition on the existence of any current representation for the		precondition on the existence of any current representation for the
	target resource.		target resource.
	If-Match = "*" / 1#entity-tag		If-Match = "*" / 1#entity-tag
	If any of the entity-tags listed in the If-Match field value match		If any of the entity-tags listed in the If-Match field value match
	(as per Section 2.2.3) the entity-tag of the selected representation		(as per Section 2.3.2) the entity-tag of the selected representation
	for the target resource, or if "*" is given and any current		for the target resource, or if "*" is given and any current
	representation exists for the target resource, then the server MAY		representation exists for the target resource, then the server MAY
	perform the request method as if the If-Match header field was not		perform the request method as if the If-Match header field was not
	present.		present.
	If none of the entity-tags match, or if "*" is given and no current		If none of the entity-tags match, or if "*" is given and no current
	representation exists, the server MUST NOT perform the requested		representation exists, the server MUST NOT perform the requested
	method. Instead, the server MUST respond with the 412 (Precondition		method. Instead, the server MUST respond with the 412 (Precondition
	Failed) status code.		Failed) status code.
	skipping to change at page 15, line 44		skipping to change at page 16, line 16
	unsafe request method (e.g., PUT) from inadvertently modifying an		unsafe request method (e.g., PUT) from inadvertently modifying an
	existing representation of the target resource when the client		existing representation of the target resource when the client
	believes that the resource does not have a current representation.		believes that the resource does not have a current representation.
	This is a variation on the "lost update" problem that might arise if		This is a variation on the "lost update" problem that might arise if
	more than one client attempts to create an initial representation for		more than one client attempts to create an initial representation for
	the target resource.		the target resource.
	If-None-Match = "*" / 1#entity-tag		If-None-Match = "*" / 1#entity-tag
	If any of the entity-tags listed in the If-None-Match field-value		If any of the entity-tags listed in the If-None-Match field-value
	match (as per Section 2.2.3) the entity-tag of the selected		match (as per Section 2.3.2) the entity-tag of the selected
	representation, or if "*" is given and any current representation		representation, or if "*" is given and any current representation
	exists for that resource, then the server MUST NOT perform the		exists for that resource, then the server MUST NOT perform the
	requested method. Instead, if the request method was GET or HEAD,		requested method. Instead, if the request method was GET or HEAD,
	the server SHOULD respond with a 304 (Not Modified) status code,		the server SHOULD respond with a 304 (Not Modified) status code,
	including the cache-related header fields (particularly ETag) of the		including the cache-related header fields (particularly ETag) of the
	selected representation that has a matching entity-tag. For all		selected representation that has a matching entity-tag. For all
	other request methods, the server MUST respond with a 412		other request methods, the server MUST respond with a 412
	(Precondition Failed) status code.		(Precondition Failed) status code.
	If none of the entity-tags match, then the server MAY perform the		If none of the entity-tags match, then the server MAY perform the
	requested method as if the If-None-Match header field did not exist,		requested method as if the If-None-Match header field did not exist,
	but MUST also ignore any If-Modified-Since header field(s) in the		but MUST also ignore any If-Modified-Since header field(s) in the
	request. That is, if no entity-tags match, then the server MUST NOT		request. That is, if no entity-tags match, then the server MUST NOT
	return a 304 (Not Modified) response.		return a 304 (Not Modified) response.
	If the request would, without the If-None-Match header field, result		If the request would, without the If-None-Match header field, result
	in anything other than a 2xx or 304 status code, then the If-None-		in anything other than a 2xx or 304 status code, then the If-None-
	Match header field MUST be ignored. (See Section 2.2.4 for a		Match header field MUST be ignored. (See Section 2.4 for a
	discussion of server behavior when both If-Modified-Since and If-		discussion of server behavior when both If-Modified-Since and If-
	None-Match appear in the same request.)		None-Match appear in the same request.)
	Examples:		Examples:
	If-None-Match: "xyzzy"		If-None-Match: "xyzzy"
	If-None-Match: W/"xyzzy"		If-None-Match: W/"xyzzy"
	If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"		If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
	If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"		If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
	If-None-Match: *		If-None-Match: *
	skipping to change at page 20, line 21		skipping to change at page 20, line 38
	5.2. Header Field Registration		5.2. Header Field Registration
	The Message Header Field Registry located at <http://www.iana.org/		The Message Header Field Registry located at <http://www.iana.org/
	assignments/message-headers/message-header-index.html> shall be		assignments/message-headers/message-header-index.html> shall be
	updated with the permanent registrations below (see [RFC3864]):		updated with the permanent registrations below (see [RFC3864]):
	+---------------------+----------+----------+-------------+		+---------------------+----------+----------+-------------+
	| Header Field Name | Protocol | Status | Reference |		| Header Field Name | Protocol | Status | Reference |
	+---------------------+----------+----------+-------------+		+---------------------+----------+----------+-------------+
	| ETag | http | standard | Section 2.2 |		| ETag | http | standard | Section 2.3 |
	| If-Match | http | standard | Section 3.1 |		| If-Match | http | standard | Section 3.1 |
	| If-Modified-Since | http | standard | Section 3.3 |		| If-Modified-Since | http | standard | Section 3.3 |
	| If-None-Match | http | standard | Section 3.2 |		| If-None-Match | http | standard | Section 3.2 |
	| If-Unmodified-Since | http | standard | Section 3.4 |		| If-Unmodified-Since | http | standard | Section 3.4 |
	| Last-Modified | http | standard | Section 2.1 |		| Last-Modified | http | standard | Section 2.2 |
	+---------------------+----------+----------+-------------+		+---------------------+----------+----------+-------------+
	The change controller is: "IETF (iesg@ietf.org) - Internet		The change controller is: "IETF (iesg@ietf.org) - Internet
	Engineering Task Force".		Engineering Task Force".
	6. Security Considerations		6. Security Considerations
	No additional security considerations have been identified beyond		No additional security considerations have been identified beyond
	those applicable to HTTP in general [Part1].		those applicable to HTTP in general [Part1].
	7. Acknowledgments		7. Acknowledgments
			See Section 12 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-15		and Message Parsing", draft-ietf-httpbis-p1-messaging-16
	(work in progress), July 2011.		(work in progress), August 2011.
	[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-15		and Content Negotiation", draft-ietf-httpbis-p3-payload-16
	(work in progress), July 2011.		(work in progress), August 2011.
	[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-15 (work		Partial Responses", draft-ietf-httpbis-p5-range-16 (work
	in progress), July 2011.		in progress), August 2011.
	[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-15 (work in		6: Caching", draft-ietf-httpbis-p6-cache-16 (work in
	progress), July 2011.		progress), August 2011.
	[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 21, line 40		skipping to change at page 22, line 11
	[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration		[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
	Procedures for Message Header Fields", BCP 90, RFC 3864,		Procedures for Message Header Fields", BCP 90, RFC 3864,
	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 2.2.2 and 3.2).		(Sections 2.1 and 3.2).
	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 [Part1], Section 6.1>		HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
	skipping to change at page 22, line 26		skipping to change at page 22, line 37
	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
	opaque-tag = quoted-string		opaque-tag = quoted-string
	quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>		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
	skipping to change at page 25, line 36		skipping to change at page 26, line 9
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle		o <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
	ABNFs for header fields"		ABNFs for header fields"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/269>: "ETags and		o <http://tools.ietf.org/wg/httpbis/trac/ticket/269>: "ETags and
	Quotes"		Quotes"
	C.16. Since draft-ietf-httpbis-p4-conditional-14		C.16. Since draft-ietf-httpbis-p4-conditional-14
	None.		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"
	Index		Index
	3		3
	304 Not Modified (status code) 18		304 Not Modified (status code) 19
	4		4
	412 Precondition Failed (status code) 19		412 Precondition Failed (status code) 20
	E		E
	ETag header field 8		ETag header field 10
	G		G
	Grammar		Grammar
	entity-tag 8		entity-tag 10
	ETag 8		ETag 10
	If-Match 14		If-Match 15
	If-Modified-Since 16		If-Modified-Since 17
	If-None-Match 15		If-None-Match 16
	If-Unmodified-Since 18		If-Unmodified-Since 18
	Last-Modified 6		Last-Modified 8
	opaque-tag 8		opaque-tag 10
	weak 8		weak 10
	H		H
	Header Fields		Header Fields
	ETag 8		ETag 10
	If-Match 14		If-Match 14
	If-Modified-Since 16		If-Modified-Since 17
	If-None-Match 15		If-None-Match 15
	If-Unmodified-Since 18		If-Unmodified-Since 18
	Last-Modified 6		Last-Modified 8
	I		I
	If-Match header field 14		If-Match header field 14
	If-Modified-Since header field 16		If-Modified-Since header field 17
	If-None-Match header field 15		If-None-Match header field 15
	If-Unmodified-Since header field 18		If-Unmodified-Since header field 18
	L		L
	Last-Modified header field 6		Last-Modified header field 8
	M		M
	metadata 6		metadata 6
	S		S
	selected representation 5		selected representation 5
	Status Codes		Status Codes
	304 Not Modified 18		304 Not Modified 19
	412 Precondition Failed 19		412 Precondition Failed 20
	V		V
	validator 6		validator 6
			strong 6
			weak 6
	Authors' Addresses		Authors' Addresses
	Roy T. Fielding (editor)		Roy T. Fielding (editor)
	Adobe Systems Incorporated		Adobe Systems Incorporated
	345 Park Ave		345 Park Ave
	San Jose, CA 95110		San Jose, CA 95110
	USA		USA
	EMail: fielding@gbiv.com		EMail: fielding@gbiv.com
End of changes. 57 change blocks.
	223 lines changed or deleted		246 lines changed or added
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