draft-nottingham-http-link-header-03.txt		draft-nottingham-http-link-header-04.txt
	Network Working Group M. Nottingham		Network Working Group M. Nottingham
	Updates: 4287 (if approved)		Updates: 4287 (if approved)
	Intended status: Standards Track		Intended status: Standards Track
	Expires: June 4, 2009		Expires: August 29, 2009
	Link Relations and HTTP Header Linking		Link Relations and HTTP Header Linking
	draft-nottingham-http-link-header-03		draft-nottingham-http-link-header-04
	Status of this Memo		Status of this Memo
	By submitting this Internet-Draft, each author represents that any		This Internet-Draft is submitted to IETF in full conformance with the
	applicable patent or other IPR claims of which he or she is aware		provisions of BCP 78 and BCP 79. This document may contain material
	have been or will be disclosed, and any of which he or she becomes		from IETF Documents or IETF Contributions published or made publicly
	aware will be disclosed, in accordance with Section 6 of BCP 79.		available before November 10, 2008. The person(s) controlling the
			copyright in some of this material may not have granted the IETF
			Trust the right to allow modifications of such material outside the
			IETF Standards Process. Without obtaining an adequate license from
			the person(s) controlling the copyright in such materials, this
			document may not be modified outside the IETF Standards Process, and
			derivative works of it may not be created outside the IETF Standards
			Process, except to format it for publication as an RFC or to
			translate it into languages other than English.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	other groups may also distribute working documents as Internet-		other groups may also distribute working documents as Internet-
	Drafts.		Drafts.
	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."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt.		http://www.ietf.org/ietf/1id-abstracts.txt.
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	This Internet-Draft will expire on June 4, 2009.		This Internet-Draft will expire on August 29, 2009.
			Copyright Notice
			Copyright (c) 2009 IETF Trust and the persons identified as the
			document authors. All rights reserved.
			This document is subject to BCP 78 and the IETF Trust's Legal
			Provisions Relating to IETF Documents in effect on the date of
			publication of this document (http://trustee.ietf.org/license-info).
			Please review these documents carefully, as they describe your rights
			and restrictions with respect to this document.
	Abstract		Abstract
	This document specifies relation types for Web links, and defines a		This document specifies relation types for Web links, and defines a
	registry for them. It also defines how to send such links in HTTP		registry for them. It also defines how to send such links in HTTP
	headers with the Link header-field.		headers with the Link header-field.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3		2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
	3. Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3		3. Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	4. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 4		4. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 4
	5. The Link Header Field . . . . . . . . . . . . . . . . . . . . 5		5. The Link Header Field . . . . . . . . . . . . . . . . . . . . 5
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 10		7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10		8. Internationalisation Considerations . . . . . . . . . . . . . 11
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 10		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
	8.2. Informative References . . . . . . . . . . . . . . . . . . 11		9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
	Appendix A. Notes on Using the Link Header with HTML . . . . . . 11		9.2. Informative References . . . . . . . . . . . . . . . . . . 12
	Appendix B. Notes on Using the Link Header with Atom . . . . . . 12		Appendix A. Notes on Using the Link Header with HTML4 . . . . . . 13
	Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 13		Appendix B. Notes on Using the Link Header with Atom . . . . . . 14
	Appendix D. Document history . . . . . . . . . . . . . . . . . . 13		Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 15
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14		Appendix D. Document history . . . . . . . . . . . . . . . . . . 15
	Intellectual Property and Copyright Statements . . . . . . . . . . 15		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
	1. Introduction		1. Introduction
	A means of indicating the relationships between documents on the Web,		A means of indicating the relationships between resources on the Web,
	as well as indicating the type of those relationships, has been		as well as indicating the type of those relationships, has been
	available for some time in HTML [W3C.REC-html401-19991224], and more		available for some time in HTML [W3C.REC-html401-19991224], and more
	recently in Atom [RFC4287]. These mechanisms, although conceptually		recently in Atom [RFC4287]. These mechanisms, although conceptually
	similar, are separate. However, links between resources need not be		similar, are separately specified. However, links between resources
	format-specific; it can be useful to have typed links that are		need not be format-specific; it can be useful to have typed links
	independent of the format, especially when a resource has		that are independent of the format, especially when a resource has
	representations in multiple formats.		representations in multiple formats.
	This document defines typed link relations, independent of the		To this end, this document defines a framework for typed links that
	context they occur in. It does so by clarifying the status of the		isn't specific to a particular serialisation or context of use. It
	link relation registry established by Atom, and registering in it the		does so by re-defining the link relation registry established by Atom
	relations that are defined by HTML.		to have a broader scope, and adding to it the relations that are
			defined by HTML.
	Furthermore, an HTTP header-field for conveying typed links was		Furthermore, an HTTP header-field for conveying typed links was
	defined in [RFC2068], but removed from [RFC2616], due to a lack of		defined in [RFC2068], but removed from [RFC2616], due to a lack of
	implementation experience. Since then, several use cases for doing		implementation experience. Since then, it has been implemented in
	so have surfaced. However, because it was removed, the status of the		some User-Agents (e.g., for stylesheets), and several additional use
	Link header is unclear, leading some to consider minting new		cases have surfaced. Because it was removed, the status of the Link
	application-specific HTTP headers instead of reusing it. This		header is unclear, leading some to consider minting new application-
	document addresses this by re-specifying the Link header with updated		specific HTTP headers instead of reusing it. This document addresses
	but backwards-compatible syntax.		this by re-specifying the Link header with updated but backwards-
			compatible syntax.
	[[ Feedback is welcome on the ietf-http-wg@w3.org mailing list,		[[ Feedback is welcome on the ietf-http-wg@w3.org mailing list,
	although this is NOT a work item of the HTTPBIS WG. ]]		although this is NOT a work item of the HTTPBIS WG. ]]
	2. Notational Conventions		2. Notational Conventions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in BCP 14, [RFC2119], as		document are to be interpreted as described in BCP 14, [RFC2119], as
	scoped to those conformance targets.		scoped to those conformance targets.
	This document uses the Augmented Backus-Naur Form (ABNF) notation of		This document uses the Augmented Backus-Naur Form (ABNF) notation of
	[RFC2616], and explicitly includes the following rules from it:		[RFC2616], and explicitly includes the following rules from it:
	quoted-string, token, SP (space). Additionally, the following rules		quoted-string, token, SP (space). Additionally, the following rules
	are included from [RFC3986]: URI and URI-Reference, and from		are included from [RFC3986]: URI and URI-Reference, and from
	[RFC4288]: type-name.		[RFC4288]: type-name.
	3. Links		3. Links
	In the context of this specification, a link is comprised of:		In this specification, a link is a typed connection between two
			resources that are identified by IRIs [RFC3987], and is comprised of:
	o A target URI ([RFC3986]), and		o A context IRI, and
	o A context of use, and
	o A link relation type (Section 4), and		o A link relation type (Section 4), and
	o A link direction (outbound or inbound).		o A target IRI.
	A link can be viewed as a statement of the form "(subject) has a		A link can be viewed as a statement of the form "(context IRI) has a
	(relation type) at (object)", where for an outbound link the subject		(relation type) resource at (target IRI)."
	is the context of use and the object is the resource identified by
	the target URI, and for an inbound link the subject is the resource
	identified by the target URI and the object is the context of use.
	This specification does not define a general syntax for expressing		Note that in the common case, the context IRI will also be a URI
	links, nor the specific context for a given link; it is expected that		[RFC3986], because HTTP requires that IRIs be converted to URIs
	applications of link relations will specify both aspects. One such		before dereferencing. Likewise, the target IRI will be converted to
	application is communication of links through HTTP headers, specified		a URI in serialisations that do not support IRIs (e.g., the Link
	in Section 5.		header).
			This specification does not place restrictions on the cardinality of
			links; there can be multiple links from and to a particular IRI, and
			multiple links of different types between two given IRIs.
			Additionally, this specification does not define a general syntax for
			expressing links, nor mandate a specific context for any given link;
			it is expected that applications of links will specify both aspects.
			One such application is communication of links through HTTP headers,
			specified in Section 5.
	Such applications may further constrain or extend links (e.g.,		Such applications may further constrain or extend links (e.g.,
	associating a media type hint, only allowing links in one direction).		associating a media type hint).
	4. Link Relation Types		4. Link Relation Types
	A link relation type identifies the semantics of a link. For		A link relation type identifies the semantics of a link. For
	example, an outbound link with the relation type "copyright"		example, a link with the relation type "copyright" indicates that the
	indicates that the resource identified is a statement of the		resource identified by the target IRI is a statement of the copyright
	copyright terms applying to the current context of the link.		terms applying to the current context IRI.
	Relation types are not to be confused with media types [RFC4288];		Relation types are not to be confused with media types [RFC4288];
	they do not identify the format of the representation that results		they do not identify the format of the representation that results
	when the link is dereferenced. Rather, they only describe how the		when the link is dereferenced. Rather, they only describe how the
	current context is related to another resource.		current context is related to another resource.
	As such, relation types are not format-specific, and MUST NOT specify		As such, relation types are not format-specific, and MUST NOT specify
	a particular format or media type that they are to be used with.		a particular format or media type that they are to be used with.
	Likewise, a relation type SHOULD NOT specify what its context of its		Likewise, the context IRI for a given link is usually determined by
	use is.		the serialisation of the link (e.g., the Link header, a HTML
			document, etc.); a relation type SHOULD NOT specify the context IRI.
	Relation types are URIs. Although specific applications of links may		Consuming implementations SHOULD ignore relation types that they do
	specify the use of URI-References, they must also indicate how to		not understand or have no need to process.
	resolve them to absolute URIs.
	Although anyone may mint a URI to be used as a relation type, it is		There are two kinds of relation types; registered and extension.
	expected that a few standard types will predominate. To facilitate
	this, Section 6.2 establishes an IANA registry of relation types that		4.1. Registered Relation Types
	share a common base URI.
			Commonly-used relation types with a clear meaning that are shared
			across applications can be registered as tokens for convenience and
			to promote reuse. For example, "self" and "alternate" are registered
			relation types, because they are broadly useful.
			This draft establishes an IANA registry of such relation types; see
			Section 6.2.
			Registered relation types MUST conform to the token rule, and SHOULD
			conform to the sgml-name rule for compatibility with deployed
			implementations;
			sgml-name = ALPHA *( ALPHA | DIGIT | "." | "-" )
			Names that differ only in case from existing entries (e.g., "Foo" and
			"foo") MUST NOT be registered.
			Registered relation types MUST be compared in a case-insensitive
			fashion.
			Although they are specified as tokens, applications wishing to
			internally refer to an extension relation type using a URI MAY do so
			by considering it relative to the base URI
			"http://www.iana.org/assignments/relation/". However, the URI form
			of a registered relation type SHOULD NOT be serialised when an
			application specifies the use of a relation type, because a consuming
			implementation may not recognise it.
			4.2. Extension Relation Types
			Applications that don't merit a registered relation type may use an
			extension relation type. An extension relation type is a URI
			[RFC3986] that, when dereferenced, SHOULD yield a document describing
			that relation type.
			Extension relation types MUST be compared in a case-sensitive
			fashion, character-by-character.
	5. The Link Header Field		5. The Link Header Field
	The Link entity-header field provides a means for conveying one or		The Link entity-header field provides a means for conveying one or
	more links in HTTP headers. It is semantically equivalent to the		more links in HTTP headers. It is semantically equivalent to the
	<LINK> element in HTML, as well as the atom:link feed-level element		<LINK> element in HTML, as well as the atom:link feed-level element
	in Atom [RFC4287].		in Atom [RFC4287].
	Link = "Link" ":" #link-value		Link = "Link" ":" #link-value
	link-value = "<" URI-Reference ">" *( ";" link-param ) )		link-value = "<" URI-Reference ">" *( ";" link-param ) )
	link-param = ( ( "rel" "=" relation-type )		link-param = ( ( "rel" "=" relation-types )
	| ( "rev" "=" relation-type )		| ( "rev" "=" relation-types )
	| ( "type" "=" type-name )		| ( "type" "=" type-name )
	| ( "title" "=" quoted-string )		| ( "title" "=" quoted-string )
			| ( "title*" "=" enc2231-string )
			| ( "anchor" "=" <"> URI-Reference <"> )
	| ( link-extension ) )		| ( link-extension ) )
	link-extension = token [ "=" ( token | quoted-string ) ]		link-extension = token [ "=" ( token | quoted-string ) ]
	relation-type = URI-Reference |		enc2231-string = <extended-value, see <xref target="RFC2231"/>,
	<"> URI-Reference *( SP URI-Reference) <">		Section 7>
			relation-types = relation-type |
			<"> relation-type *( SP relation-type ) <">
			relation-type = reg-relation-type | ext-relation-type
			reg-relation-type = token
			ext-relation-type = URI
	For example:		For example:
	Link: <http://example.com/TheBook/chapter2>; rel="previous";		Link: <http://example.com/TheBook/chapter2>; rel="previous";
	title="previous chapter"		title="previous chapter"
	indicates that chapter2 is previous to this resource in a logical		indicates that chapter2 is previous to this resource in a logical
	navigation path.		navigation path.
	Each link-value conveys one target URI inside angle brackets ("<>").		Each link-value conveys one target IRI as a URI-Reference (after
	If it is relative, it MUST be resolved as per [RFC3986]. Note that		conversion, if necessary) inside angle brackets ("<>"). If the URI-
	because it is conveyed in a header, base URIs from content are not		Reference is relative, it MUST be resolved as per [RFC3986]. Note
	applied to it.		that any base IRI from the body's content is not applied.
	The context of links conveyed in the Link header field is the
	representation that the header is part of.
	Each link-value MUST have at least one "rel" or "rev" parameter whose		By default, the context of a link conveyed in the Link header field
	value indicates the relation type. If the "rel" parameter is used,		is the IRI associated with the representation it occurs in. When
	it indicates that the link's direction for that relation type is		present, the anchor parameter overrides this with another URI, such
	outbound; if the "rev" parameter is used, the given relation type's		as a fragment of this resource, or a third resource (i.e., when the
	direction is inbound.		anchor value is an absolute URI).
	If the relation-type is a relative URI, its base URI MUST be		Normally, the relation type of a link is conveyed in the "rel"
	considered to be "http://www.iana.org/assignments/relation/", and the		parameter's value. The "rev" parameter has also been used for this
	corresponding value MUST be present in the link relation registry.		purpose historically by some formats, and is included here for
			compatibility with those uses, but its use is not encouraged nor
			defined by this specification.
	Relation-types that include a semicolon (";") or comma (",") MUST be		Note that extension relation types are REQUIRED to be absolute URIs
	quoted.		in Link headers, and MUST be quoted if they contain a semicolon (";")
			or comma (",").
	The title parameter MAY be used to label the destination of a link		The title parameter is used to label the destination of a link such
	such that it can be used as identification within a human-readable		that it can be used as a human-readable identifier (e.g. a menu
	menu.		entry). The title* parameter MAY be used to instead to encode this
			label in an alternate character set, and/or contain language
			information as per [RFC2231]. When using the enc2231-string syntax,
			producers MUST NOT use a charset value other than 'ISO-8859-1' or
			'UTF-8'.
	Note that link-values may contain multiple relations; for example		Note that link-values may convey multiple links between the same
			target and context IRIs; for example
	Link: <http://example.org/>; rel="index start";		Link: <http://example.org/>; rel=index;
	rel="http://example.net/relation/other";		rel="start http://example.net/relation/other"
	rev=copyright
	Here, the link "http://example.org/" has outbound links of the types		Here, the link to "http://example.org/" has the registered relation
	"http://www.iana.org/assignments/relation/index",		types "index" and "start", and the extension relation type
	"http://www.iana.org/assignments/relation/start", and		"http://example.net/relation/other".
	"http://example.net/relation/other", as well as an inbound link of
	type "http://www.iana.org/assignments/relation/copyright".
	6. IANA Considerations		6. IANA Considerations
	6.1. Link Header Registration		6.1. Link Header Registration
	This specification updates the Message Header Registry entry for		This specification updates the Message Header Registry entry for
	"Link" in HTTP [RFC3864] to refer to this document.		"Link" in HTTP [RFC3864] to refer to this document.
	Header field: Link		Header field: Link
	Applicable protocol: http		Applicable protocol: http
	skipping to change at page 6, line 42		skipping to change at page 7, line 46
	Specification document(s):		Specification document(s):
	[ this document ]		[ this document ]
	6.2. Link Relation Type Registry		6.2. Link Relation Type Registry
	This specification establishes the Link Relation Type Registry,		This specification establishes the Link Relation Type Registry,
	located at <http://www.iana.org/assignments/relation/>, and updates		located at <http://www.iana.org/assignments/relation/>, and updates
	Atom [RFC4287] to refer to it in place of the "Registry of Link		Atom [RFC4287] to refer to it in place of the "Registry of Link
	Relations".		Relations".
	The semantics of relation types is described in Section 4. This		The requirements for registered relation types are described in
	registry is intended to contain widely-used, standard relation types		Section 4.1.
	so that they may be used in "short form" (i.e., as a relative URI) in
	applications that allow this.
	Registered relation types have an implicit base URI of
	<http://www.iana.org/assignments/relation/>, and their name SHOULD be
	limited to the sgml-name rule for simplicity and backwards-
	compatibility.
	sgml-name = ALPHA *( ALPHA | DIGIT | "." | "-" )
	Names that differ only in case (e.g., "Foo" and "foo") MUST NOT be		Relation types may be registered on the advice of a Designated Expert
	registered.		(appointed by the IESG or their delegate), with a Specification
			Required (using terminology from [RFC5226]).
	New relation types can be registered by IETF Review, as outlined in		Registration requests consist of the completed registration template
	[RFC5226]. Specifications of new values should use the following		below, typically published in an RFC or Open Standard (in the sense
	template:		described by [RFC2026], section 7). However, to allow for the
			allocation of values prior to publication, the Designated Expert may
			approve registration once they are satisfied that an RFC (or other
			Open Standard) will be published.
	o Relation Name:		o Relation Name:
	o Description:		o Description:
	o Reference:		o Reference:
			Upon receiving a registration request (usually via IANA), the
			Designated Expert should request review and comment from the apps-
			discuss mailing list (or a successor designated by the APPS Area
			Directors). Before a period of 30 days has passed, the Designated
			Expert will either approve or deny the registration request,
			communicating this decision both to the review list and to IANA.
			Denials should include an explanation and, if applicable, suggestions
			as to how to make the request successful.
	The Link Relation Type registry's initial contents are:		The Link Relation Type registry's initial contents are:
	o Relation Name: alternate		o Relation Name: alternate
	o Description: Designates a substitute for the link's context.		o Description: Designates a substitute for the link's context.
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	o Relation Name: appendix		o Relation Name: appendix
	o Description: Refers to an appendix.		o Description: Refers to an appendix.
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	skipping to change at page 7, line 44		skipping to change at page 9, line 4
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	o Relation Name: contents		o Relation Name: contents
	o Description: Refers to a table of contents.		o Description: Refers to a table of contents.
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	o Relation Name: copyright		o Relation Name: copyright
	o Description: Refers to a copyright statement that applies to the		o Description: Refers to a copyright statement that applies to the
	link's context.		link's context.
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	o Relation Name: current		o Relation Name: current
	o Description: Refers to a resource containing the most recent		o Description: Refers to a resource containing the most recent
	item(s) in a collection of resources.		item(s) in a collection of resources.
	o Reference: [RFC5005]		o Reference: [RFC5005]
			o Relation Name: describedby
			o Description: Refers to a resource providing information about the
			link's context.
			o Documentation: <http://www.w3.org/TR/powder-dr/>
	o Relation Name: edit		o Relation Name: edit
	o Description: Refers to a resource that can be used to edit the		o Description: Refers to a resource that can be used to edit the
	link's context.		link's context.
	o Reference: [RFC5023]		o Reference: [RFC5023]
	o Relation Name: edit-media		o Relation Name: edit-media
	o Description: Refers to a resource that can be used to edit media		o Description: Refers to a resource that can be used to edit media
	associated with the link's context.		associated with the link's context.
	o Reference: [RFC5023]		o Reference: [RFC5023]
	o Relation Name: enclosure		o Relation Name: enclosure
	o Description: Identifies a related resource that is potentially		o Description: Identifies a related resource that is potentially
	large and might require special handling.		large and might require special handling.
	o Reference: [RFC4287]		o Reference: [RFC4287]
	o Relation Name: first		o Relation Name: first
	o Description: A URI that refers to the furthest preceding resource		o Description: An IRI that refers to the furthest preceding resource
	in a series of resources.		in a series of resources.
	o Reference: <http://www.iana.org/assignments/link-relations/first>		o Reference: <http://www.iana.org/assignments/link-relations/first>
	o Relation Name: glossary		o Relation Name: glossary
	o Description: Refers to a glossary of terms.		o Description: Refers to a glossary of terms.
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	o Relation Name: help		o Relation Name: help
	o Description: Refers to a resource offering help (more information,		o Description: Refers to a resource offering help (more information,
	links to other sources information, etc.)		links to other sources information, etc.)
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	o Relation Name: index		o Relation Name: index
	o Description: Refers to an index.		o Description: Refers to an index.
	o Reference: [W3C.REC-html401-19991224]		o Reference: [W3C.REC-html401-19991224]
	o Relation Name: last		o Relation Name: last
	o Description: A URI that refers to the furthest following resource		o Description: An IRI that refers to the furthest following resource
	in a series of resources.		in a series of resources.
	o Reference: <http://www.iana.org/assignments/link-relations/last>		o Reference: <http://www.iana.org/assignments/link-relations/last>
	o Relation Name: license		o Relation Name: license
	o Description: Refers to a license associated with the link's		o Description: Refers to a license associated with the link's
	context.		context.
	o Reference: [RFC4946]		o Reference: [RFC4946]
	o Relation Name: next		o Relation Name: next
	o Description: Refers to the next resource in a ordered series of		o Description: Refers to the next resource in a ordered series of
	resources.		resources.
	skipping to change at page 10, line 25		skipping to change at page 11, line 38
	o Reference: [RFC4287]		o Reference: [RFC4287]
	7. Security Considerations		7. Security Considerations
	The content of the Link header-field is not secure, private or		The content of the Link header-field is not secure, private or
	integrity-guaranteed, and due caution should be exercised when using		integrity-guaranteed, and due caution should be exercised when using
	it.		it.
	Applications that take advantage of typed links should consider the		Applications that take advantage of typed links should consider the
	attack vectors opened by automatically following, trusting, or		attack vectors opened by automatically following, trusting, or
	otherwise using links gathered from HTTP headers.		otherwise using links gathered from HTTP headers. In particular,
			Link headers that use the "anchor" parameter to associate a link's
			context with another resource should be treated with due caution.
	8. References		8. Internationalisation Considerations
	8.1. Normative References		Target IRIs may need to be converted to URIs in order to serialise
			them in applications that do not support IRIs. This includes the
			Link HTTP header.
			Similarly, the anchor parameter of the Link header does not support
			IRIs, and therefore IRIs must be converted to URIs before inclusion
			there.
			Relation types are defined as URIs, not IRIs, to aid in their
			comparison. It is not expected that they will be displayed to end
			users.
			9. References
			9.1. Normative References
			[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
			3", BCP 9, RFC 2026, October 1996.
	[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.
			[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
			Word Extensions: Character Sets, Languages, and
			Continuations", RFC 2231, November 1997.
	[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,		[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext		Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
	Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.		Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
	[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.
	[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform		[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
	Resource Identifier (URI): Generic Syntax", STD 66,		Resource Identifier (URI): Generic Syntax", STD 66,
	RFC 3986, January 2005.		RFC 3986, January 2005.
			[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
			Identifiers (IRIs)", RFC 3987, January 2005.
	[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and		[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
	Registration Procedures", BCP 13, RFC 4288, December 2005.		Registration Procedures", BCP 13, RFC 4288, December 2005.
	[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an		[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
	IANA Considerations Section in RFCs", BCP 26, RFC 5226,		IANA Considerations Section in RFCs", BCP 26, RFC 5226,
	May 2008.		May 2008.
	8.2. Informative References		9.2. Informative References
	[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.		[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
	Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",		Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
	RFC 2068, January 1997.		RFC 2068, January 1997.
	[RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication		[RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication
	Format", RFC 4287, December 2005.		Format", RFC 4287, December 2005.
	[RFC4685] Snell, J., "Atom Threading Extensions", RFC 4685,		[RFC4685] Snell, J., "Atom Threading Extensions", RFC 4685,
	September 2006.		September 2006.
	skipping to change at page 11, line 32		skipping to change at page 13, line 22
	September 2007.		September 2007.
	[RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing		[RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
	Protocol", RFC 5023, October 2007.		Protocol", RFC 5023, October 2007.
	[W3C.REC-html401-19991224]		[W3C.REC-html401-19991224]
	Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01		Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01
	Specification", W3C REC REC-html401-19991224,		Specification", W3C REC REC-html401-19991224,
	December 1999.		December 1999.
	Appendix A. Notes on Using the Link Header with HTML		Appendix A. Notes on Using the Link Header with HTML4
	HTML motivated the original syntax of the Link header, and many of		HTML motivated the original syntax of the Link header, and many of
	the design decisions in this document are driven by a desire to stay		the design decisions in this document are driven by a desire to stay
	compatible with these uses.		compatible with these uses.
	In HTML4, the link element can be mapped to links as specified here		In HTML4, the link element can be mapped to links as specified here
	by using the "href" attribute for the target URI, and "rel" and rev"		by using the "href" attribute for the target URI, and "rel" to convey
	to convey both the relation type and its direction, as in the Link		both the relation type, as in the Link header. The context of the
	header. The context of the link is generally the entire HTML		link is the URI associated with the entire HTML document.
	document.
			HTML4 also has a "rev" parameter for links that allows a link's
			relation to be reversed. The Link header has a "rev" parameter to
			allow the expression of these links in HTTP headers, but its use is
			not encouraged, due to the confusion this mechanism causes as well as
			conflicting interpretations among HTML versions.
	All of the link relations defined by HTML4 have been included in the		All of the link relations defined by HTML4 have been included in the
	link relation registry, so they can be used without modification.		link relation registry, so they can be used without modification.
	However, extension link relations work differently in HTML4 and the		However, extension link relations work differently in HTML4 and the
	Link header; the former uses a document-wide "profile" URI to scope		Link header; the former uses a document-wide "profile" URI to scope
	the relations, while the latter allows the use of full URIs on		the relations, while the latter allows the use of full URIs on
	individual relations.		individual relations.
	Therefore, when using the profile mechanism in HTML4, it is necessary		Therefore, when using the profile mechanism in HTML4, it is necessary
	to map the profiled link relations to URIs when expressed in Link		to map the profiled link relations to URIs when expressed in Link
	headers. For example, in HTML:		headers. For example, in HTML:
	<html>		<html>
	<head profile="http://example.com/profile1/">		<head profile="http://example.com/profile1/">
	<link rel="foo" href="/foo">		<link rel="foo" href="/bar">
	</head>		</head>
	[...]		[...]
	could be represented as a header like this;		could be represented as a header like this;
	Link: </foo>; rel="http://example.com/profile1/foo"		Link: </bar>; rel="http://example.com/profile1/foo"
	Profile authors should note this when creating profile URIs; it may		Profile authors should note this when creating profile URIs; it may
	be desirable to use URIs that end in a delimiter (e.g., "/" or "#"),		be desirable to use URIs that end in a delimiter (e.g., "/" or "#"),
	to make extracting the specific relation in use easier.		to make extracting the specific relation in use easier.
	HTML defines link relation values as case-insensitive, while the Link		Surveys of existing HTML content have shown that unregistered link
	header's syntax does not. Therefore, it is important to case-		relation types that are not URIs are (perhaps inevitably) common.
	normalise relation values in HTML before comparing or converting them		Consuming HTML implementations should not consider such unregistered
	to Link headers.		short links to be errors, but rather relation types with a local
			scope (i.e., their meaning is specific and perhaps private to that
			document).
	HTML also defines several attributes on links that are not explicitly		HTML4 also defines several attributes on links that are not
	defined by the Link header. Although most of these are believed to		explicitly defined by the Link header. These attributes can be
	be defunct, they can be used as link-extensions.		serialised as link-extensions to maintain fidelity.
	Appendix B. Notes on Using the Link Header with Atom		Appendix B. Notes on Using the Link Header with Atom
	Atom conveys links in the atom:link element, with the "href"		Atom conveys links in the atom:link element, with the "href"
	attribute indicating the target URI and the "rel" attribute		attribute indicating the target IRI and the "rel" attribute
	containing the relation type. The context of the link is either a		containing the relation type. The context of the link is either a
	feed or an entry, depending on where it appears; generally, feed-		feed IRI or an entry ID, depending on where it appears; generally,
	level links are candidates for transmission as a Link header. Since		feed-level links are candidates for transmission as a Link header.
	atom:link only specifies "rel", only outbound links are allowed by
	non-extended Atom syntax.
	When serialising an atom:link into a Link header, it is necessary to		When serialising an atom:link into a Link header, it is necessary to
	convert IRIs (if used) to URIs. Additionally, since the base URI for		convert target IRIs (if used) to URIs.
	link relations in Link headers is fixed, extension relation types
	(i.e,. those not in the registry) must be represented as absolute		Atom defines extension relation types in terms of IRIs. This
	URIs.		specification defines them as URIs, to aid in their comparison.
			Atom allows registered link relation types to be serialised as
			absolute URIs, because a base URI is defined for the registry. Such
			relation types SHOULD be converted to the appropriate registered form
			(e.g., "http://www.iana.org/assignments/relation/self" to "self") so
			that they are not mistaken for extension relation types.
	Note also that while the Link header allows multiple relations to be		Note also that while the Link header allows multiple relations to be
	associated with a single link, atom:link does not. In this case, a		associated with a single link, atom:link does not. In this case, a
	single link-value may map to several atom:link elements.		single link-value may map to several atom:link elements.
	As with HTML, atom:link defines some attributes that are not		As with HTML, atom:link defines some attributes that are not
	explicitly mirrored in the Link header syntax, but they may also be		explicitly mirrored in the Link header syntax, but they may also be
	used as link-extensions.		used as link-extensions.
	Appendix C. Acknowledgements		Appendix C. Acknowledgements
	This specification lifts the idea and definition for the Link header		This specification lifts the idea and definition for the Link header
	from RFC2068; credit for it belongs entirely to the authors of and		from RFC2068; credit for it belongs entirely to the authors of and
	contributors to that document. The link relation registrations		contributors to that document. The link relation registrations
	themselves are sourced from several documents; see the applicable		themselves are sourced from several documents; see the applicable
	references.		references.
	The author would like to thank the many people who commented upon,		The author would like to thank the many people who commented upon,
	encouraged and gave feedback to this draft, especially including		encouraged and gave feedback to this draft, especially including
	Frank Ellermann and Julian Reschke.		Frank Ellermann, Roy Fielding and Julian Reschke.
	Appendix D. Document history		Appendix D. Document history
	[[ to be removed by the RFC editor before publication as an RFC. ]]		[[ to be removed by the RFC editor before publication as an RFC. ]]
	-03		-04
			o Defined context as a resource, rather than a representation.
			o Removed concept of link directionality; relegated to a deprecated
			Link header extension.
			o Relation types split into registered (non-URI) and extension
			(URI).
			o Changed wording around finding URIs for registered relation types.
			o Changed target and context URIs to IRIs (but not extension
			relation types).
			o Add RFC2231 encoding for title parameter, explicit BNF for title*.
			o Add i18n considerations.
			o Specify how to compare relation types.
			o Changed registration procedure to Designated Expert.
			o Softened language around presence of relations in the registry.
			o Added describedby relation.
			o Re-added 'anchor' parameter, along with security consideration for
			third-party anchors.
			o Softened language around HTML4 attributes that aren't directly
			accommodated.
			o Various tweaks to abstract, introduction and examples.
			-03
	o Inverted focus from Link headers to link relations.		o Inverted focus from Link headers to link relations.
	o Specified was a link relation type is.		o Specified was a link relation type is.
	o Based on discussion, re-added 'rev'.		o Based on discussion, re-added 'rev'.
	o Changed IESG Approval to IETF Consensus for relation registrations		o Changed IESG Approval to IETF Consensus for relation registrations
	(i.e., require a document).		(i.e., require a document).
	o Updated RFC2434 reference to RFC5226.		o Updated RFC2434 reference to RFC5226.
	o Registered relations SHOULD conform to sgml-name.		o Registered relations SHOULD conform to sgml-name.
	o Cautioned against confusing relation types with media types.		o Cautioned against confusing relation types with media types.
	-02		-02
	skipping to change at page 15, line 4		skipping to change at line 738
	-00		-00
	o Initial draft; normative text lifted from RFC2068.		o Initial draft; normative text lifted from RFC2068.
	Author's Address		Author's Address
	Mark Nottingham		Mark Nottingham
	Email: mnot@mnot.net		Email: mnot@mnot.net
	URI: http://www.mnot.net/		URI: http://www.mnot.net/
	Full Copyright Statement
	Copyright (C) The IETF Trust (2008).
	This document is subject to the rights, licenses and restrictions
	contained in BCP 78, and except as set forth therein, the authors
	retain all their rights.
	This document and the information contained herein are provided on an
	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
	THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
	OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
	THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Intellectual Property
	The IETF takes no position regarding the validity or scope of any
	Intellectual Property Rights or other rights that might be claimed to
	pertain to the implementation or use of the technology described in
	this document or the extent to which any license under such rights
	might or might not be available; nor does it represent that it has
	made any independent effort to identify any such rights. Information
	on the procedures with respect to rights in RFC documents can be
	found in BCP 78 and BCP 79.
	Copies of IPR disclosures made to the IETF Secretariat and any
	assurances of licenses to be made available, or the result of an
	attempt made to obtain a general license or permission for the use of
	such proprietary rights by implementers or users of this
	specification can be obtained from the IETF on-line IPR repository at
	http://www.ietf.org/ipr.
	The IETF invites any interested party to bring to its attention any
	copyrights, patents or patent applications, or other proprietary
	rights that may cover technology that may be required to implement
	this standard. Please address the information to the IETF at
	ietf-ipr@ietf.org.
End of changes. 57 change blocks.
	141 lines changed or deleted		281 lines changed or added
This html diff was produced by rfcdiff 1.34. The latest version is available from http://tools.ietf.org/tools/rfcdiff/