< draft-fielding-uri-rfc2396bis-01.txt		draft-fielding-uri-rfc2396bis-02.txt >
	Network Working Group T. Berners-Lee		Network Working Group T. Berners-Lee
	Internet-Draft MIT/LCS		Internet-Draft MIT/LCS
	Updates: 1738 (if approved) R. Fielding		Updates: 1738 (if approved) R. Fielding
	Obsoletes: 2732, 2396, 1808 (if approved) Day Software		Obsoletes: 2732, 2396, 1808 (if approved) Day Software
	Expires: September 1, 2003 L. Masinter		L. Masinter
	Adobe		Expires: November 21, 2003 Adobe
	March 3, 2003		May 23, 2003
	Uniform Resource Identifier (URI): Generic Syntax		Uniform Resource Identifier (URI): Generic Syntax
	draft-fielding-uri-rfc2396bis-01		draft-fielding-uri-rfc2396bis-02
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is in full conformance with		This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC2026.		all provisions of Section 10 of RFC2026.
	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 other		Task Force (IETF), its areas, and its working groups. Note that other
	groups may also distribute working documents as Internet-Drafts.		groups may also distribute working documents as Internet-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 September 1, 2003.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2003). All Rights Reserved.		Copyright (C) The Internet Society (2003). All Rights Reserved.
	Abstract		Abstract
	A Uniform Resource Identifier (URI) is a compact string of characters		A Uniform Resource Identifier (URI) is a compact string of characters
	for identifying an abstract or physical resource. This document		for identifying an abstract or physical resource. This document
	defines the generic syntax of a URI, including both absolute and		defines the generic syntax of a URI, including both absolute and
	skipping to change at page 2, line 11 ¶		skipping to change at page 2, line 9 ¶
	such that an implementation can parse the common components of a URI		such that an implementation can parse the common components of a URI
	reference without knowing the scheme-specific requirements of every		reference without knowing the scheme-specific requirements of every
	possible identifier type. This document does not define a generative		possible identifier type. This document does not define a generative
	grammar for all URIs; that task will be performed by the individual		grammar for all URIs; that task will be performed by the individual
	specifications of each URI scheme.		specifications of each URI scheme.
	Editorial Note		Editorial Note
	Discussion of this draft and comments to the editors should be sent		Discussion of this draft and comments to the editors should be sent
	to the uri@w3.org mailing list. An issues list and version history		to the uri@w3.org mailing list. An issues list and version history
	is available at <http://www.apache.org/~fielding/uri/rev-2002/>.		is available at <http://www.apache.org/~fielding/uri/rev-2002/
			issues.html>.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
	1.1 Overview of URIs . . . . . . . . . . . . . . . . . . . . . . 4		1.1 Overview of URIs . . . . . . . . . . . . . . . . . . . . . . 4
	1.2 URI, URL, and URN . . . . . . . . . . . . . . . . . . . . . 5		1.1.1 Generic Syntax . . . . . . . . . . . . . . . . . . . . . . . 5
	1.3 Example URIs . . . . . . . . . . . . . . . . . . . . . . . . 6		1.1.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	1.4 Hierarchical URIs and Relative Forms . . . . . . . . . . . . 6		1.1.3 URI, URL, and URN . . . . . . . . . . . . . . . . . . . . . 6
	1.5 URI Transcribability . . . . . . . . . . . . . . . . . . . . 7		1.2 Design Considerations . . . . . . . . . . . . . . . . . . . 6
	1.6 Syntax Notation and Common Elements . . . . . . . . . . . . 8		1.2.1 Transcription . . . . . . . . . . . . . . . . . . . . . . . 6
	2. URI Characters and Escape Sequences . . . . . . . . . . . . 9		1.2.2 Separating Identification from Interaction . . . . . . . . . 7
	2.1 URIs and non-ASCII characters . . . . . . . . . . . . . . . 9		1.2.3 Hierarchical Identifiers . . . . . . . . . . . . . . . . . . 9
			1.3 Syntax Notation . . . . . . . . . . . . . . . . . . . . . . 9
			2. Characters . . . . . . . . . . . . . . . . . . . . . . . . . 10
			2.1 Encoding of Characters . . . . . . . . . . . . . . . . . . . 10
	2.2 Reserved Characters . . . . . . . . . . . . . . . . . . . . 10		2.2 Reserved Characters . . . . . . . . . . . . . . . . . . . . 10
	2.3 Unreserved Characters . . . . . . . . . . . . . . . . . . . 11		2.3 Unreserved Characters . . . . . . . . . . . . . . . . . . . 11
	2.4 Escape Sequences . . . . . . . . . . . . . . . . . . . . . . 11		2.4 Escaped Characters . . . . . . . . . . . . . . . . . . . . . 12
	2.4.1 Escaped Encoding . . . . . . . . . . . . . . . . . . . . . . 11		2.4.1 Escaped Encoding . . . . . . . . . . . . . . . . . . . . . . 12
	2.4.2 When to Escape and Unescape . . . . . . . . . . . . . . . . 11		2.4.2 When to Escape and Unescape . . . . . . . . . . . . . . . . 12
	2.4.3 Excluded US-ASCII Characters . . . . . . . . . . . . . . . . 12		2.5 Excluded Characters . . . . . . . . . . . . . . . . . . . . 13
	3. URI Syntactic Components . . . . . . . . . . . . . . . . . . 14		3. Syntax Components . . . . . . . . . . . . . . . . . . . . . 15
	3.1 Scheme Component . . . . . . . . . . . . . . . . . . . . . . 15		3.1 Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
	3.2 Authority Component . . . . . . . . . . . . . . . . . . . . 15		3.2 Authority . . . . . . . . . . . . . . . . . . . . . . . . . 16
	3.2.1 Registry-based Naming Authority . . . . . . . . . . . . . . 16		3.2.1 User Information . . . . . . . . . . . . . . . . . . . . . . 16
	3.2.2 Server-based Naming Authority . . . . . . . . . . . . . . . 16		3.2.2 Host . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
	3.3 Path Component . . . . . . . . . . . . . . . . . . . . . . . 18		3.2.3 Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
	3.4 Query Component . . . . . . . . . . . . . . . . . . . . . . 19		3.3 Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
	4. URI References . . . . . . . . . . . . . . . . . . . . . . . 20		3.4 Query . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
	4.1 Fragment Identifier . . . . . . . . . . . . . . . . . . . . 20		3.5 Fragment . . . . . . . . . . . . . . . . . . . . . . . . . . 20
	4.2 Same-document References . . . . . . . . . . . . . . . . . . 21		4. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
	4.3 Parsing a URI Reference . . . . . . . . . . . . . . . . . . 21		4.1 URI Reference . . . . . . . . . . . . . . . . . . . . . . . 22
	5. Relative URI References . . . . . . . . . . . . . . . . . . 22		4.2 Relative URI . . . . . . . . . . . . . . . . . . . . . . . . 22
	5.1 Establishing a Base URI . . . . . . . . . . . . . . . . . . 23		4.3 Absolute URI . . . . . . . . . . . . . . . . . . . . . . . . 23
	5.1.1 Base URI within Document Content . . . . . . . . . . . . . . 24		4.4 Same-document Reference . . . . . . . . . . . . . . . . . . 23
	5.1.2 Base URI from the Encapsulating Entity . . . . . . . . . . . 24		4.5 Suffix Reference . . . . . . . . . . . . . . . . . . . . . . 23
	5.1.3 Base URI from the Retrieval URI . . . . . . . . . . . . . . 25		5. Relative Resolution . . . . . . . . . . . . . . . . . . . . 25
	5.1.4 Default Base URI . . . . . . . . . . . . . . . . . . . . . . 25		5.1 Establishing a Base URI . . . . . . . . . . . . . . . . . . 25
	5.2 Resolving Relative References to Absolute Form . . . . . . . 25		5.1.1 Base URI within Document Content . . . . . . . . . . . . . . 26
	6. URI Normalization and Comparison . . . . . . . . . . . . . . 29		5.1.2 Base URI from the Encapsulating Entity . . . . . . . . . . . 26
	6.1 URI Equivalence . . . . . . . . . . . . . . . . . . . . . . 29		5.1.3 Base URI from the Retrieval URI . . . . . . . . . . . . . . 27
	6.2 Comparison Ladder . . . . . . . . . . . . . . . . . . . . . 29		5.1.4 Default Base URI . . . . . . . . . . . . . . . . . . . . . . 27
	6.2.1 Simple String Comparison . . . . . . . . . . . . . . . . . . 30		5.2 Obtaining the Referenced URI . . . . . . . . . . . . . . . . 27
	6.2.2 Syntax-based Normalization . . . . . . . . . . . . . . . . . 31		5.3 Recomposition of a Parsed URI . . . . . . . . . . . . . . . 29
	6.2.3 Scheme-based Normalization . . . . . . . . . . . . . . . . . 32		5.4 Examples of Relative Resolution . . . . . . . . . . . . . . 30
	6.2.4 Protocol-based Normalization . . . . . . . . . . . . . . . . 32		5.4.1 Normal Examples . . . . . . . . . . . . . . . . . . . . . . 30
	6.3 Good Practice When Using URIs . . . . . . . . . . . . . . . 32		5.4.2 Abnormal Examples . . . . . . . . . . . . . . . . . . . . . 31
	7. Security Considerations . . . . . . . . . . . . . . . . . . 34		6. Normalization and Comparison . . . . . . . . . . . . . . . . 33
	7.1 Reliability and Consistency . . . . . . . . . . . . . . . . 34		6.1 Equivalence . . . . . . . . . . . . . . . . . . . . . . . . 33
	7.2 Malicious Construction . . . . . . . . . . . . . . . . . . . 34		6.2 Comparison Ladder . . . . . . . . . . . . . . . . . . . . . 33
	7.3 Rare IP Address Formats . . . . . . . . . . . . . . . . . . 35		6.2.1 Simple String Comparison . . . . . . . . . . . . . . . . . . 34
	7.4 Sensitive Information . . . . . . . . . . . . . . . . . . . 35		6.2.2 Syntax-based Normalization . . . . . . . . . . . . . . . . . 35
	7.5 Semantic Attacks . . . . . . . . . . . . . . . . . . . . . . 36		6.2.3 Scheme-based Normalization . . . . . . . . . . . . . . . . . 36
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37		6.2.4 Protocol-based Normalization . . . . . . . . . . . . . . . . 36
	Normative References . . . . . . . . . . . . . . . . . . . . 38		6.3 Canonical Form . . . . . . . . . . . . . . . . . . . . . . . 36
	Non-normative References . . . . . . . . . . . . . . . . . . 39		7. Security Considerations . . . . . . . . . . . . . . . . . . 38
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 40		7.1 Reliability and Consistency . . . . . . . . . . . . . . . . 38
	A. Collected BNF for URI . . . . . . . . . . . . . . . . . . . 42		7.2 Malicious Construction . . . . . . . . . . . . . . . . . . . 38
	B. Parsing a URI Reference with a Regular Expression . . . . . 43		7.3 Rare IP Address Formats . . . . . . . . . . . . . . . . . . 39
	C. Examples of Resolving Relative URI References . . . . . . . 44		7.4 Sensitive Information . . . . . . . . . . . . . . . . . . . 39
	C.1 Normal Examples . . . . . . . . . . . . . . . . . . . . . . 44		7.5 Semantic Attacks . . . . . . . . . . . . . . . . . . . . . . 39
	C.2 Abnormal Examples . . . . . . . . . . . . . . . . . . . . . 44		8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 41
	D. Embedding the Base URI in HTML documents . . . . . . . . . . 46		Normative References . . . . . . . . . . . . . . . . . . . . 42
	E. Recommendations for Delimiting URI in Context . . . . . . . 47		Informative References . . . . . . . . . . . . . . . . . . . 43
	F. Abbreviated URIs . . . . . . . . . . . . . . . . . . . . . . 49		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 45
	G. Summary of Non-editorial Changes . . . . . . . . . . . . . . 50		A. Collected ABNF for URI . . . . . . . . . . . . . . . . . . . 46
	G.1 Additions . . . . . . . . . . . . . . . . . . . . . . . . . 50		B. Parsing a URI Reference with a Regular Expression . . . . . 47
	G.2 Modifications from RFC 2396 . . . . . . . . . . . . . . . . 50		C. Embedding the Base URI in HTML documents . . . . . . . . . . 48
	Index . . . . . . . . . . . . . . . . . . . . . . . . . . . 52		D. Delimiting a URI in Context . . . . . . . . . . . . . . . . 49
	Intellectual Property and Copyright Statements . . . . . . . 55		E. Summary of Non-editorial Changes . . . . . . . . . . . . . . 51
			E.1 Additions . . . . . . . . . . . . . . . . . . . . . . . . . 51
			E.2 Modifications from RFC 2396 . . . . . . . . . . . . . . . . 51
			Index . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
			Intellectual Property and Copyright Statements . . . . . . . 57
	1. Introduction		1. Introduction
	A Uniform Resource Identifier (URI) provides a simple and extensible		A Uniform Resource Identifier (URI) provides a simple and extensible
	means for identifying a resource. This specification of URI syntax		means for identifying a resource. This specification of URI syntax
	and semantics is derived from concepts introduced by the World Wide		and semantics is derived from concepts introduced by the World Wide
	Web global information initiative, whose use of such objects dates		Web global information initiative, whose use of such identifiers
	from 1990 and is described in "Universal Resource Identifiers in WWW"		dates from 1990 and is described in "Universal Resource Identifiers
	[RFC1630], and is designed to meet the recommendations laid out in		in WWW" [RFC1630], and is designed to meet the recommendations laid
	"Functional Recommendations for Internet Resource Locators" [RFC1736]		out in "Functional Recommendations for Internet Resource Locators"
	and "Functional Requirements for Uniform Resource Names" [RFC1737].		[RFC1736] and "Functional Requirements for Uniform Resource Names"
			[RFC1737].
	This document obsoletes [RFC2396], which merged "Uniform Resource		This document obsoletes [RFC2396], which merged "Uniform Resource
	Locators" [RFC1738] and "Relative Uniform Resource Locators"		Locators" [RFC1738] and "Relative Uniform Resource Locators"
	[RFC1808] in order to define a single, generic syntax for all URIs.		[RFC1808] in order to define a single, generic syntax for all URIs.
	It excludes those portions of RFC 1738 that defined the specific		It excludes those portions of RFC 1738 that defined the specific
	syntax of individual URI schemes; those portions will be updated as		syntax of individual URI schemes; those portions will be updated as
	separate documents. The process for registration of new URI schemes		separate documents. The process for registration of new URI schemes
	is defined separately by [RFC2717].		is defined separately by [RFC2717].
	All significant changes from RFC 2396 are noted in Appendix G.		All significant changes from RFC 2396 are noted in Appendix G.
	1.1 Overview of URIs		1.1 Overview of URIs
	URIs are characterized by the following definitions:		URIs are characterized as follows:
	Uniform		Uniform
	Uniformity provides several benefits: it allows different types of		Uniformity provides several benefits: it allows different types of
	resource identifiers to be used in the same context, even when the		resource identifiers to be used in the same context, even when the
	mechanisms used to access those resources may differ; it allows		mechanisms used to access those resources may differ; it allows
	uniform semantic interpretation of common syntactic conventions		uniform semantic interpretation of common syntactic conventions
	across different types of resource identifiers; it allows		across different types of resource identifiers; it allows
	introduction of new types of resource identifiers without		introduction of new types of resource identifiers without
	interfering with the way that existing identifiers are used; and,		interfering with the way that existing identifiers are used; and,
	it allows the identifiers to be reused in many different contexts,		it allows the identifiers to be reused in many different contexts,
	thus permitting new applications or protocols to leverage a		thus permitting new applications or protocols to leverage a
	pre-existing, large, and widely-used set of resource identifiers.		pre-existing, large, and widely-used set of resource identifiers.
	Resource		Resource
	A resource can be anything that has identity. Familiar examples		Anything that can be named or described can be a resource.
	include an electronic document, an image, a service (e.g.,		Familiar examples include an electronic document, an image, a
	"today's weather report for Los Angeles"), and a collection of		service (e.g., "today's weather report for Los Angeles"), and a
	other resources. Not all resources are network "retrievable";		collection of other resources. A resource is not necessarily
	e.g., human beings, corporations, and bound books in a library can		accessible via the Internet; e.g., human beings, corporations, and
	also be considered resources.		bound books in a library can also be resources. Likewise, abstract
			concepts can be resources, such as the operators and operands of a
	The resource is the conceptual mapping to an entity or set of		mathematical equation or the types of a relationship (e.g.,
	entities, not necessarily the entity which corresponds to that		"parent" or "employee").
	mapping at any particular instance in time. Thus, a resource can
	remain constant even when its content---the entities to which it
	currently corresponds---changes over time, provided that the
	conceptual mapping is not changed in the process.
	Identifier		Identifier
	An identifier is an object that can act as a reference to		An identifier embodies the information required to distinguish
	something that has identity. In the case of a URI, the object is		what is being identified from all other things within its scope of
	a sequence of characters with a restricted syntax.		identification.
	Having identified a resource, a system may perform a variety of
	operations on the resource, as might be characterized by such words
	as `access', `update', `replace', or `find attributes'.
	1.2 URI, URL, and URN
	A URI can be further classified as a locator, a name, or both. The		A URI is an identifier that consists of a sequence of characters
	term "Uniform Resource Locator" (URL) refers to the subset of URIs		matching the restricted syntax defined by this specification. A URI
	that, in addition to identifying the resource, provide a means of		can be used to refer to a resource. This specification does not
	locating the resource by describing its primary access mechanism		place any limits on the nature of a resource or the reasons why an
	(e.g., its network "location"). The term "Uniform Resource Name"		application might wish to refer to a resource. URIs have a global
	(URN) refers to the subset of URIs that are required to remain		scope and should be interpreted consistently regardless of context,
	globally unique and persistent even when the resource ceases to exist		but that interpretation may be defined in relation to the user's
	or becomes unavailable.		context (e.g., "http://localhost/" refers to a resource that is
			relative to the user's network interface and yet not specific to any
			one user).
	An individual scheme does not need to be cast into one of a discrete		1.1.1 Generic Syntax
	set of URI types such as "URL", "URN", "URC", etc. Any given URI
	scheme may define subspaces that have the characteristics of a name,
	a locator, or both, often depending on the persistence and care in
	the assignment of identifiers by the naming authority, rather than on
	any quality of the URI scheme. For that reason, this specification
	deprecates use of the terms URL or URN to distinguish between
	schemes, instead using the term URI throughout.
	Each URI scheme (Section 3.1) defines the namespace of the URI, and		Each URI begins with a scheme name, as defined in Section 3.1, that
	thus may further restrict the syntax and semantics of identifiers		refers to a specification for assigning identifiers within that
	using that scheme. This specification defines those elements of the		scheme. As such, the URI syntax is a federated and extensible naming
	URI syntax that are either required of all URI schemes or are common		system wherein each scheme's specification may further restrict the
	to many URI schemes. It thus defines the syntax and semantics that		syntax and semantics of identifiers using that scheme.
	are needed to implement a scheme-independent parsing mechanism for
	URI references, such that the scheme-dependent handling of a URI can
	be postponed until the scheme-dependent semantics are needed.
	Although many URI schemes are named after protocols, this does not		This specification defines those elements of the URI syntax that are
	imply that use of such a URI will result in access to the resource		required of all URI schemes or are common to many URI schemes. It
	via the named protocol. URIs are often used in contexts that are		thus defines the syntax and semantics that are needed to implement a
	purely for identification, just like any other identifier. Even when		scheme-independent parsing mechanism for URI references, such that
	a URI is used to obtain a representation of a resource, that access		the scheme-dependent handling of a URI can be postponed until the
	might be through gateways, proxies, caches, and name resolution		scheme-dependent semantics are needed. Likewise, protocols and data
	services that are independent of the protocol of the resource origin,		formats that make use of URI references can refer to this
	and the resolution of some URIs may require the use of more than one		specification as defining the range of syntax allowed for all URIs,
	protocol (e.g., both DNS and HTTP are typically used to access an		including those schemes that have yet to be defined.
	"http" URI's resource when it can't be found in a local cache).
	A parser of the generic URI syntax is capable of parsing any URI		A parser of the generic URI syntax is capable of parsing any URI
	reference into its major components; once the scheme is determined,		reference into its major components; once the scheme is determined,
	further scheme-specific parsing can be performed on the components.		further scheme-specific parsing can be performed on the components.
	In other words, the URI generic syntax is a superset of the syntax of		In other words, the URI generic syntax is a superset of the syntax of
	all URI schemes.		all URI schemes.
	1.3 Example URIs		1.1.2 Examples
	The following examples illustrate URIs that are in common use.		The following examples illustrate URIs that are in common use.
	ftp://ftp.is.co.za/rfc/rfc1808.txt		ftp://ftp.is.co.za/rfc/rfc1808.txt
	-- ftp scheme for File Transfer Protocol services		-- ftp scheme for File Transfer Protocol services
	gopher://gopher.tc.umn.edu:70/11/Mailing%20Lists/		gopher://gopher.tc.umn.edu:70/11/Mailing%20Lists/
	-- gopher scheme for Gopher and Gopher+ Protocol services		-- gopher scheme for Gopher and Gopher+ Protocol services
	http://www.ietf.org/rfc/rfc2396.txt		http://www.ietf.org/rfc/rfc2396.txt
	skipping to change at page 6, line 40 ¶		skipping to change at page 6, line 27 ¶
	mailto:John.Doe@example.com		mailto:John.Doe@example.com
	-- mailto scheme for electronic mail addresses		-- mailto scheme for electronic mail addresses
	news:comp.infosystems.www.servers.unix		news:comp.infosystems.www.servers.unix
	-- news scheme for USENET news groups and articles		-- news scheme for USENET news groups and articles
	telnet://melvyl.ucop.edu/		telnet://melvyl.ucop.edu/
	-- telnet scheme for interactive TELNET services		-- telnet scheme for interactive TELNET services
	1.4 Hierarchical URIs and Relative Forms		1.1.3 URI, URL, and URN
	An absolute identifier refers to a resource independent of the		A URI can be further classified as a locator, a name, or both. The
	context in which the identifier is used. In contrast, a relative		term "Uniform Resource Locator" (URL) refers to the subset of URIs
	identifier refers to a resource by describing the difference within a		that, in addition to identifying the resource, provide a means of
	hierarchical namespace between the current context and an absolute		locating the resource by describing its primary access mechanism
	identifier of the resource.		(e.g., its network "location"). The term "Uniform Resource Name"
			(URN) refers to the subset of URIs that are required to remain
			globally unique and persistent even when the resource ceases to exist
			or becomes unavailable.
	Some URI schemes support a hierarchical naming system, where the		An individual scheme does not need to be classified as being just one
	hierarchy of the name is denoted by a "/" delimiter separating the		of "name" or "locator". Instances of URIs from any given scheme may
	components in the scheme. This document defines a scheme-independent		have the characteristics of names or locators or both, often
	`relative' form of URI reference that can be used in conjunction with		depending on the persistence and care in the assignment of
	a `base' URI of a hierarchical scheme to produce the `absolute' URI		identifiers by the naming authority, rather than any quality of the
	form of the reference. The syntax of a hierarchical URI is described		scheme. This specification deprecates use of the term "URN" for
	in Section 3; the relative URI calculation is described in Section 5.		anything but URIs in the "urn" scheme [RFC2141]. This specification
			also deprecates the term "URL".
	1.5 URI Transcribability		1.2 Design Considerations
	The URI syntax was designed with global transcribability as one of		1.2.1 Transcription
	its main concerns. A URI is a sequence of characters from a very
	limited set, i.e. the letters of the basic Latin alphabet, digits,		The URI syntax has been designed with global transcription as one of
			its main considerations. A URI is a sequence of characters from a
			very limited set: the letters of the basic Latin alphabet, digits,
	and a few special characters. A URI may be represented in a variety		and a few special characters. A URI may be represented in a variety
	of ways: e.g., ink on paper, pixels on a screen, or a sequence of		of ways: e.g., ink on paper, pixels on a screen, or a sequence of
	octets in a coded character set. The interpretation of a URI depends		octets in a coded character set. The interpretation of a URI depends
	only on the characters used and not how those characters are		only on the characters used and not how those characters are
	represented in a network protocol.		represented in a network protocol.
	The goal of transcribability can be described by a simple scenario.		The goal of transcription can be described by a simple scenario.
	Imagine two colleagues, Sam and Kim, sitting in a pub at an		Imagine two colleagues, Sam and Kim, sitting in a pub at an
	international conference and exchanging research ideas. Sam asks Kim		international conference and exchanging research ideas. Sam asks Kim
	for a location to get more information, so Kim writes the URI for the		for a location to get more information, so Kim writes the URI for the
	research site on a napkin. Upon returning home, Sam takes out the		research site on a napkin. Upon returning home, Sam takes out the
	napkin and types the URI into a computer, which then retrieves the		napkin and types the URI into a computer, which then retrieves the
	information to which Kim referred.		information to which Kim referred.
	There are several design concerns revealed by the scenario:		There are several design considerations revealed by the scenario:
	o A URI is a sequence of characters, which is not always represented		o A URI is a sequence of characters that is not always represented
	as a sequence of octets.		as a sequence of octets.
	o A URI may be transcribed from a non-network source, and thus		o A URI might be transcribed from a non-network source, and thus
	should consist of characters that are most likely to be able to be		should consist of characters that are most likely to be able to be
	typed into a computer, within the constraints imposed by keyboards		entered into a computer, within the constraints imposed by
	(and related input devices) across languages and locales.		keyboards (and related input devices) across languages and
			locales.
	o A URI often needs to be remembered by people, and it is easier for		o A URI often needs to be remembered by people, and it is easier for
	people to remember a URI when it consists of meaningful		people to remember a URI when it consists of meaningful or
	components.		familiar components.
	These design concerns are not always in alignment. For example, it		These design considerations are not always in alignment. For
	is often the case that the most meaningful name for a URI component		example, it is often the case that the most meaningful name for a URI
	would require characters that cannot be typed into some systems. The		component would require characters that cannot be typed into some
	ability to transcribe the resource identifier from one medium to		systems. The ability to transcribe a resource identifier from one
	another was considered more important than having its URI consist of		medium to another has been considered more important than having a
	the most meaningful of components. In local and regional contexts		URI consist of the most meaningful of components. In local or
	and with improving technology, users might benefit from being able to		regional contexts and with improving technology, users might benefit
	use a wider range of characters; such use is not defined in this		from being able to use a wider range of characters; such use is not
	document.		defined in this document.
	1.6 Syntax Notation and Common Elements		1.2.2 Separating Identification from Interaction
	This document uses two conventions to describe and define the syntax		A common misunderstanding of URIs is that they are only used to refer
	for URI. The first, called the layout form, is a general description		to accessible resources. In fact, the URI alone only provides
	of the order of components and component separators, as in		identification; access to the resource is neither guaranteed nor
			implied by the presence of a URI. Instead, an operation (if any)
			associated with a URI reference is defined by the protocol element,
			data format attribute, or natural language text in which it appears.
	<first>/<second>;<third>?<fourth>		Given a URI, a system may attempt to perform a variety of operations
			on the resource, as might be characterized by such words as "denote",
			"access", "update", "replace", or "find attributes". Such operations
			are defined by the protocols that make use of URIs, not by this
			specification. However, we do use a few general terms for describing
			common operations on URIs. URI "resolution" is the process of
			determining an access mechanism and the appropriate parameters
			necessary to dereference a URI; such resolution may require several
			iterations. Using that access mechanism to perform some action on
			the URI's resource is termed a "dereference" of the URI.
	The component names are enclosed in angle-brackets and any characters		When URIs are used within information systems to identify sources of
	outside angle-brackets are literal separators. Whitespace should be		information, the most common form of URI dereference is "retrieval":
	ignored. These descriptions are used informally and do not define		making use of a URI in order to retrieve a representation of its
	the syntax requirements.		associated resource. A "representation" is a sequence of octets,
			along with metadata describing those octets, that constitutes a
			record of the state of the resource at the time that the
			representation is generated. Retrieval is achieved by a process that
			might include using the URI as a cache key to check for a locally
			cached representation, resolution of the URI to determine an
			appropriate access mechanism (if any), and dereference of the URI for
			the sake of applying a retrieval operation.
	The second convention is a formal grammar defined using the Augmented		URI references in information systems are designed to be
	Backus-Naur Form (ABNF) notation of [RFC2234]. Although the ABNF		late-binding: the result of an access is generally determined at the
	defines syntax in terms of the ASCII character encoding [ASCII], the		time it is accessed and may vary over time or due to other aspects of
	URI syntax should be interpreted in terms of the character that the		the interaction. When an author creates a reference to such a
	ASCII-encoded octet represents, rather than the octet encoding		resource, they do so with the intention that the reference be used in
	itself. How a URI is represented in terms of bits and bytes on the		the future; what is being identified is not some specific result that
	wire is dependent upon the character encoding of the protocol used to		was obtained in the past, but rather some characteristic that is
	transport it, or the charset of the document that contains it.		expected to be true for future results. In such cases, the resource
			referred to by the URI is actually a sameness of characteristics as
			observed over time, perhaps elucidated by additional comments or
			assertions made by the resource provider.
	The complete URI syntax is collected in Appendix A.		Although many URI schemes are named after protocols, this does not
			imply that use of such a URI will result in access to the resource
			via the named protocol. URIs are often used simply for the sake of
			identification. Even when a URI is used to retrieve a representation
			of a resource, that access might be through gateways, proxies,
			caches, and name resolution services that are independent of the
			protocol associated with the scheme name, and the resolution of some
			URIs may require the use of more than one protocol (e.g., both DNS
			and HTTP are typically used to access an "http" URI's origin server
			when a representation isn't found in a local cache).
	2. URI Characters and Escape Sequences		1.2.3 Hierarchical Identifiers
	A URI consists of a restricted set of characters, primarily chosen		The URI syntax is organized hierarchically, with components listed in
	to aid transcribability and usability both in computer systems and in		decreasing order from left to right. For some URI schemes, the
	non-computer communications. Characters used conventionally as		visible hierarchy is limited to the scheme itself: everything after
	delimiters around a URI are excluded. The restricted set of		the scheme component delimiter is considered opaque to URI
	characters consists of digits, letters, and a few graphic symbols		processing. Other URI schemes make the hierarchy explicit and visible
	chosen from those common to most of the character encodings and input		to generic parsing algorithms.
	facilities available to Internet users.
	uric = reserved / unreserved / escaped		The URI syntax reserves the slash ("/"), question-mark ("?"), and
			crosshatch ("#") characters for the purpose of delimiting components
			that are significant to the generic parser's hierarchical
			interpretation of an identifier. In addition to aiding the
			readability of such identifiers through the consistent use of
			familiar syntax, this uniform representation of hierarchy across
			naming schemes allows scheme-independent references to be made
			relative to that hierarchy.
	Within a URI, characters are either used as delimiters or to		An "absolute" URI refers to a resource independent of the naming
	represent strings of data (octets) within the delimited portions.		hierarchy in which the identifier is used. In contrast, a "relative"
	Octets are either represented directly by a character (using the		URI refers to a resource by describing the difference within a
	US-ASCII character for that octet [ASCII]) or by an escape encoding.		hierarchical name space between the current context and an absolute
	This representation is elaborated below.		URI of the resource. Section 4.2 defines a scheme-independent form
			of relative URI reference that can be used in conjunction with a base
			URI of a hierarchical scheme to produce the absolute URI form of that
			reference.
	2.1 URIs and non-ASCII characters		1.3 Syntax Notation
	The relationship between URIs and characters has been a source of		This document uses the Augmented Backus-Naur Form (ABNF) notation of
	confusion for characters that are not part of US-ASCII. To describe		[RFC2234] to define the URI syntax. Although the ABNF defines syntax
	the relationship, it is useful to distinguish between a "character"		in terms of the US-ASCII character encoding [ASCII], the URI syntax
	(as a distinguishable semantic entity) and an "octet" (an 8-bit		should be interpreted in terms of the character that the
	byte). There are two mappings, one from URI characters to octets, and		ASCII-encoded octet represents, rather than the octet encoding
	a second from octets to original characters:		itself. How a URI is represented in terms of bits and bytes on the
			wire is dependent upon the character encoding of the protocol used to
			transport it, or the charset of the document that contains it.
	URI character sequence->octet sequence->original character sequence		The following core ABNF productions are used by this specification as
			defined by Section 6.1 of [RFC2234]: ALPHA, CR, CTL, DIGIT, DQUOTE,
			HEXDIG, LF, OCTET, and SP. The complete URI syntax is collected in
			Appendix A.
	A URI is represented as a sequence of characters, not as a sequence		2. Characters
	of octets. That is because a URI might be "transported" by means that
	are not through a computer network, e.g., printed on paper, read over
	the radio, etc.
	Within a delimited component of a URI, a sequence of characters is		A URI consists of a restricted set of characters, primarily chosen
	used to represent a sequence of octets. For example, the character		to aid transcription and usability both in computer systems and in
	"a" represents the octet 97 (decimal), while the character sequence		non-computer communications. Characters used conventionally as
	"%", "0", "a" represents the octet 10 (decimal).		delimiters around a URI are excluded. The set of URI characters
			consists of digits, letters, and a few graphic symbols chosen from
			those common to most of the character encodings and input facilities
			available to Internet users.
	There is a second translation for some resources: the sequence of		uric = reserved / unreserved / escaped
	octets defined by a component of the URI is subsequently used to
	represent a sequence of characters. A 'charset' defines this mapping.
	There are many charsets in use in Internet protocols. For example,
	UTF-8 [UTF-8] defines a mapping from sequences of octets to sequences
	of characters in the repertoire of ISO 10646.
	In the simplest case, the original character sequence contains only		Within a URI, reserved characters are used to delimit syntax
	characters that are defined in US-ASCII, and the two levels of		components, unreserved characters are used to describe registered
	mapping are simple and easily invertible: each 'original character'		names, and unreserved, non-delimiting reserved, and escaped
	is represented as the octet for the US-ASCII code for it, which is,		characters are used to represent strings of data (1*OCTET) within the
	in turn, represented as either the US-ASCII character, or else the		components.
	"%" escape sequence for that octet.
	For original character sequences that contain non-ASCII characters,		2.1 Encoding of Characters
	however, the situation is more difficult. Internet protocols that
	transmit octet sequences intended to represent character sequences
	are expected to provide some way of identifying the charset used, if
	there might be more than one [RFC2277]. However, there is currently
	no provision within the generic URI syntax to accomplish this
	identification. An individual URI scheme may require a single
	charset, define a default charset, or provide a way to indicate the
	charset used. For example, a new scheme "foo" might be defined such
	that any escaped octet is keyed to the UTF-8 encoding in order to
	determine the corresponding Unicode character.
	It is expected that a systematic treatment of character encoding		As described above (Section 1.3), the URI syntax is defined in terms
	within URIs will be developed as a future modification of this		of characters by reference to the US-ASCII encoding of characters to
	specification.		octets. This specification does not mandate the use of any
			particular mapping between its character set and the octets used to
			store or transmit those characters.
			URI characters representing strings of data within a component may,
			if allowed by the component production, represent an arbitrary
			sequence of octets. For example, portions of a given URI might
			correspond to a filename on a non-ASCII file system, a query on
			non-ASCII data, numeric coordinates on a map, etc. Some URI schemes
			define a specific encoding of raw data to US-ASCII characters as part
			of their scheme-specific requirements. Most URI schemes represent
			data octets by the US-ASCII character corresponding to that octet,
			either directly in the form of the character's glyph or by use of an
			escape triplet (Section 2.4).
			When a URI scheme defines a component that represents textual data
			consisting of characters from the Unicode (ISO 10646) character set,
			we recommend that the data be encoded first as octets according to
			the UTF-8 [UTF-8] character encoding, and then escaping any octets
			that are not in the unreserved character set.
	2.2 Reserved Characters		2.2 Reserved Characters
	Many URI include components consisting of or delimited by, certain		URIs include components and sub-components that are delimited by
	special characters. These characters are called "reserved", since		certain special characters. These characters are called "reserved",
	their usage within the URI component is limited to their reserved		since their usage within a URI component is limited to their reserved
	purpose. If the data for a URI component would conflict with the		purpose within that component. If data for a URI component would
	reserved purpose, then the conflicting data must be escaped before		conflict with the reserved purpose, then the conflicting data must be
	forming the URI.		escaped (Section 2.4) before forming the URI.
	reserved = "[" / "]" / ";" / "/" / "?" /		reserved = "/" / "?" / "#" / "[" / "]" / ";" /
	":" / "@" / "&" / "=" / "+" / "$" / ","		":" / "@" / "&" / "=" / "+" / "$" / ","
	The "reserved" syntax class above refers to those characters that are		Reserved characters are used as delimiters of the generic URI
	allowed within a URI, but which may not be allowed within a		components described in Section 3, as well as within those components
	particular component of the generic URI syntax; they are used as		for delimiting sub-components. A component's ABNF syntax rule will
	delimiters of the components described in Section 3.		not use the "reserved" production directly; instead, each rule lists
			those reserved characters that are allowed within that component.
			Allowed reserved characters that are not assigned a sub-component
			delimiter role by this specification should be considered reserved
			for special use by whatever software generates the URI (i.e., they
			may be used to delimit or indicate information that is significant to
			interpretation of the identifier, but that significance is outside
			the scope of this specification). Outside of the URI's origin, a
			reserved character cannot be escaped without fear of changing how it
			will be interpreted; likewise, an escaped octet that corresponds to a
			reserved character cannot be unescaped outside the software that is
			responsible for interpreting it during URI resolution.
	Characters in the "reserved" set are not reserved in all contexts.		The slash ("/"), question-mark ("?"), and crosshatch ("#") characters
	The set of characters actually reserved within any given URI		are reserved in all URI for the purpose of delimiting components that
	component is defined by that component. In general, a character is		are significant to the generic parser's hierarchical interpretation
	reserved if the semantics of the URI changes if the character is		of an identifier. The hierarchical prefix of a URI, wherein the
	replaced with its escaped US-ASCII encoding.		slash ("/") character signifies a hierarchy delimiter, extends from
			the scheme (Section 3.1) through to the first question-mark ("?"),
			crosshatch ("#"), or the end of the URI string. In other words, the
			slash ("/") character is not treated as a hierarchical separator
			within the query (Section 3.4) and fragment (Section 3.5) components
			of a URI, but is still considered reserved within those components
			for purposes outside the scope of this specification.
	2.3 Unreserved Characters		2.3 Unreserved Characters
	Data characters that are allowed in a URI but do not have a reserved		Data characters that are allowed in a URI but do not have a reserved
	purpose are called unreserved. These include upper and lower case		purpose are called unreserved. These include uppercase and lowercase
	letters, decimal digits, and a limited set of punctuation marks and		letters, decimal digits, and a limited set of punctuation marks and
	symbols.		symbols.
	unreserved = ALPHA / DIGIT / mark		unreserved = ALPHA / DIGIT / mark
	mark = "-" / "_" / "." / "!" / "~" / "*" / "'" / "(" / ")"		mark = "-" / "_" / "." / "!" / "~" / "*" / "'" / "(" / ")"
	Unreserved characters can be escaped without changing the semantics		Unreserved characters can be escaped without changing the semantics
	of the URI, but this should not be done unless the URI is being used		of a URI, but this should not be done unless the URI is being used in
	in a context that does not allow the unescaped character to appear.		a context that does not allow the unescaped character to appear. URI
	URI normalization processes may unescape sequences in the ranges of		normalization processes may unescape sequences in the ranges of ALPHA
	ALPHA (%41-%5A and %61-%7A), DIGIT (%30-%39), underscore (%5F), or		(%41-%5A and %61-%7A), DIGIT (%30-%39), hyphen (%2D), underscore
	tilde (%7E) without fear of creating a conflict, but unescaping the		(%5F), or tilde (%7E) without fear of creating a conflict, but
	other mark characters is usually counterproductive.		unescaping the other mark characters is usually counterproductive.
	2.4 Escape Sequences		2.4 Escaped Characters
	Data must be escaped if it does not have a representation using an		Data must be escaped if it does not have a representation using an
	unreserved character; this includes data that does not correspond to		unreserved character; this includes data that does not correspond to
	a printable character of the US-ASCII coded character set, or that		a printable character of the US-ASCII coded character set or
	corresponds to any US-ASCII character that is disallowed, as		corresponds to a US-ASCII character that delimits the component from
	explained below.		others, is reserved in that component for delimiting sub-components,
			or is excluded from any use within a URI (Section 2.5).
	2.4.1 Escaped Encoding		2.4.1 Escaped Encoding
	An escaped octet is encoded as a character triplet, consisting of		An escaped octet is encoded as a character triplet, consisting of
	the percent character "%" followed by the two hexadecimal digits		the percent character "%" followed by the two hexadecimal digits
	representing the octet code in . For example, "%20" is the escaped		representing that octet's numeric value. For example, "%20" is the
	encoding for the US-ASCII space character.		escaped encoding for the US-ASCII space character (SP). This is
			sometimes referred to as "percent-encoding" the octet.
	escaped = "%" HEXDIG HEXDIG		escaped = "%" HEXDIG HEXDIG
			The uppercase hexadecimal digits 'A' through 'F' are equivalent to
			the lowercase digits 'a' through 'f', respectively. Two URIs that
			differ only in the case of hexadecimal digits used in escaped octets
			are equivalent. For consistency, we recommend that uppercase digits
			be used by URI generators and normalizers.
	2.4.2 When to Escape and Unescape		2.4.2 When to Escape and Unescape
	A URI is always in an "escaped" form, since escaping or unescaping a		Under normal circumstances, the only time that characters within a
	completed URI might change its semantics. Normally, the only time		URI string are escaped is during the process of generating the URI
	escape encodings can safely be made is when the URI is being created		from its component parts. Each component may have its own set of
	from its component parts; each component may have its own set of
	characters that are reserved, so only the mechanism responsible for		characters that are reserved, so only the mechanism responsible for
	generating or interpreting that component can determine whether or		generating or interpreting that component can determine whether or
	not escaping a character will change its semantics. Likewise, a URI		not escaping a character will change its semantics. The exception is
	must be separated into its components before the escaped characters		when a URI is being used within a context where the unreserved "mark"
	within those components can be safely decoded.		characters might need to be escaped, such as when used for a
			command-line argument or within a single-quoted attribute.
			Once generated, a URI is always in an escaped form. When a URI is
			resolved, the components significant to that scheme-specific
			resolution process (if any) must be parsed and separated before the
			escaped characters within those components can be safely unescaped.
	In some cases, data that could be represented by an unreserved		In some cases, data that could be represented by an unreserved
	character may appear escaped; for example, some of the unreserved		character may appear escaped; for example, some of the unreserved
	"mark" characters are automatically escaped by some systems. If the		"mark" characters are automatically escaped by some systems. A URI
	given URI scheme defines a canonicalization algorithm, then		normalizer may unescape escaped octets that are represented by
	unreserved characters may be unescaped according to that algorithm.		characters in the unreserved set. For example, "%7E" is sometimes
	For example, "%7e" is sometimes used instead of "~" in an http URI		used instead of tilde ("~") in an "http" URI path and can be
	path, but the two are equivalent for an http URI.		converted to "~" without changing the interpretation of the URI.
	Because the percent "%" character always has the reserved purpose of		Because the percent ("%") character serves as the escape indicator,
	being the escape indicator, it must be escaped as "%25" in order to		it must be escaped as "%25" in order for that octet to be used as
	be used as data within a URI. Implementers should be careful not to		data within a URI. Implementers should be careful not to escape or
	escape or unescape the same string more than once, since unescaping		unescape the same string more than once, since unescaping an already
	an already unescaped string might lead to misinterpreting a percent		unescaped string might lead to misinterpreting a percent data
	data character as another escaped character, or vice versa in the		character as another escaped character, or vice versa in the case of
	case of escaping an already escaped string.		escaping an already escaped string.
	2.4.3 Excluded US-ASCII Characters		2.5 Excluded Characters
	Although they are disallowed within the URI syntax, we include here a		Although they are disallowed within the URI syntax, we include here
	description of those US-ASCII characters that have been excluded and		a description of those characters that have been excluded and the
	the reasons for their exclusion.		reasons for their exclusion.
			excluded = invisible / delims / unwise
	The control characters (CTL) in the US-ASCII coded character set are		The control characters (CTL) in the US-ASCII coded character set are
	not used within a URI, both because they are non-printable and		not used within a URI, both because they are non-printable and
	because they are likely to be misinterpreted by some control		because they are likely to be misinterpreted by some control
	mechanisms.		mechanisms. The space character (SP) is excluded because significant
			spaces may disappear and insignificant spaces may be introduced when
	The space character (SP) is excluded because significant spaces may		a URI is transcribed, typeset, or subjected to the treatment of
	disappear and insignificant spaces may be introduced when a URI is
	transcribed or typeset or subjected to the treatment of
	word-processing programs. Whitespace is also used to delimit a URI		word-processing programs. Whitespace is also used to delimit a URI
	in many contexts.		in many contexts. Characters outside the US-ASCII set are excluded as
			well.
	The angle-bracket "<" and ">" and double-quote (") characters are		invisible = CTL / SP / %x80-FF
			The angle-bracket ("<" and ">") and double-quote (") characters are
	excluded because they are often used as the delimiters around a URI		excluded because they are often used as the delimiters around a URI
	in text documents and protocol fields. The character "#" is excluded		in text documents and protocol fields. The percent character ("%")
	because it is used to delimit a URI from a fragment identifier in a		is excluded because it is used for the encoding of escaped (Section
	URI reference (Section 4). The percent character "%" is excluded		2.4) characters.
	because it is used for the encoding of escaped characters.
	delims = "<" / ">" / "#" / "%" / DQUOTE		delims = "<" / ">" / "%" / DQUOTE
	Other characters are excluded because gateways and other transport		Other characters are excluded because gateways and other transport
	agents are known to sometimes modify such characters, or they are		agents are known to sometimes modify such characters.
	used as delimiters.
	unwise = "{" / "}" / "|" / "\" / "^" / "`"		unwise = "{" / "}" / "|" / "\" / "^" / "`"
	Data corresponding to excluded characters must be escaped in order to		Data octets corresponding to excluded characters must be escaped in
	be properly represented within a URI.		order to be represented within a URI.
	3. URI Syntactic Components
	The URI syntax is dependent upon the scheme. In general, absolute
	URIs are written as follows:
	<scheme>:<scheme-specific-part>
	An absolute URI contains the name of the scheme being used (<scheme>)
	followed by a colon (":") and then a string (the
	<scheme-specific-part>) whose interpretation depends on the scheme.
	The URI syntax does not require that the scheme-specific-part have
	any general structure or set of semantics which is common among all
	URIs. However, a subset of URI do share a common syntax for
	representing hierarchical relationships within the namespace. This
	"generic URI" syntax consists of a sequence of four main components:
	<scheme>://<authority><path>?<query>
	each of which, except <scheme>, may be absent from a particular URI.
	For example, some URI schemes do not allow an <authority> component,
	and others do not use a <query> component.
	absolute-URI = scheme ":" ( hier-part / opaque-part )
	URIs that are hierarchical in nature use the slash "/" character for
	separating hierarchical components. For some file systems, a "/"
	character (used to denote the hierarchical structure of a URI) is the
	delimiter used to construct a file name hierarchy, and thus the URI
	path will look similar to a file pathname. This does NOT imply that
	the resource is a file or that the URI maps to an actual filesystem
	pathname.
	hier-part = [ net-path / abs-path ] [ "?" query ]		3. Syntax Components
	net-path = "//" authority [ abs-path ]		The generic URI syntax consists of a hierarchical sequence of
			components referred to as the scheme, authority, path, query, and
			fragment.
	abs-path = "/" path-segments		URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
	URIs that do not make use of the slash "/" character for separating		hier-part = net-path / abs-path / rel-path
	hierarchical components are considered opaque by the generic URI
	parser.
	opaque-part = uric-no-slash *uric		net-path = "//" authority [ abs-path ]
			abs-path = "/" path-segments
			rel-path = path-segments
	uric-no-slash = unreserved / escaped / "[" / "]" / ";" / "?" /		The scheme and path components are required, though path may be empty
	":" / "@" / "&" / "=" / "+" / "$" / ","		(no characters). An ABNF-driven parser of hier-part will find that
			the three productions in the rule are ambiguous: they are
			disambiguated by the "first-match-wins" (a.k.a. "greedy") algorithm.
			In other words, if the string begins with two slash characters ("//
			"), then it is a net-path; if it begins with only one slash
			character, then it is an abs-path; otherwise, it is a rel-path. Note
			that rel-path does not necessarily contain any slash ("/")
			characters; a non-hierarchical path will be treated as opaque data by
			a generic URI parser.
	We use the term <path> to refer to both the <abs-path> and		The authority component is only present when a string matches the
	<opaque-part> constructs, since they are mutually exclusive for any		net-path production. Since the presence of an authority component
	given URI and can be parsed as a single component.		restricts the remaining syntax for path, we have not included a
			specific "path" rule in the syntax. Instead, what we refer to as the
			URI path is that part of the parsed URI string matching the abs-path
			or rel-path production in the syntax above, since they are mutually
			exclusive for any given URI and can be parsed as a single component.
	3.1 Scheme Component		3.1 Scheme
	Just as there are many different methods of access to resources,		Each URI begins with a scheme name that refers to a specification for
	there are a variety of schemes for identifying such resources. The		assigning identifiers within that scheme. As such, the URI syntax is
	URI syntax consists of a sequence of components separated by reserved		a federated and extensible naming system wherein each scheme's
	characters, with the first component defining the semantics for the		specification may further restrict the syntax and semantics of
	remainder of the URI string.		identifiers using that scheme.
	Scheme names consist of a sequence of characters beginning with a		Scheme names consist of a sequence of characters beginning with a
	lower case letter and followed by any combination of lower case		letter and followed by any combination of letters, digits, plus
	letters, digits, plus ("+"), period ("."), or hyphen ("-"). For		("+"), period ("."), or hyphen ("-"). Although scheme is
	resiliency, programs interpreting a URI should treat upper case		case-insensitive, the canonical form is lowercase and documents that
	letters as equivalent to lower case in scheme names (e.g., allow		specify schemes must do so using lowercase letters. An
	"HTTP" as well as "http").		implementation should accept uppercase letters as equivalent to
			lowercase in scheme names (e.g., allow "HTTP" as well as "http"), for
	scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )		the sake of robustness, but should only generate lowercase scheme
			names, for consistency.
	Relative URI references are distinguished from absolute URI in that
	they do not begin with a scheme name. Instead, the scheme is
	inherited from the base URI, as described in Section 5.2.
	3.2 Authority Component
	Many URI schemes include a top hierarchical element for a naming
	authority, such that the namespace defined by the remainder of the
	URI is governed by that authority. This authority component is
	typically defined by an Internet-based server or a scheme-specific
	registry of naming authorities.
	authority = server / reg-name
	The authority component is preceded by a double slash "//" and is
	terminated by the next slash "/", question-mark "?", or by the end of
	the URI. Within the authority component, the characters ";", ":",
	"@", "?", "/", "[", and "]" are reserved.
	An authority component is not required for a URI scheme to make use		scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
	of relative references. A base URI without an authority component
	implies that any relative reference will also be without an authority
	component.
	3.2.1 Registry-based Naming Authority		Individual schemes are not specified by this document. The process
			for registration of new URI schemes is defined separately by
			[RFC2717]. The scheme registry maintains the mapping between scheme
			names and their specifications.
	The structure of a registry-based naming authority is specific to		3.2 Authority
	the URI scheme, but constrained to the allowed characters for an
	authority component.
	reg-name = 1*( unreserved / escaped / ";" /		Many URI schemes include a hierarchical element for a naming
	":" / "@" / "&" / "=" / "+" / "$" / "," )		authority, such that governance of the name space defined by the
			remainder of the URI is delegated to that authority (which may, in
			turn, delegate it further). The generic syntax provides a common
			means for distinguishing an authority based on a registered domain
			name or server address, along with optional port and user
			information.
	3.2.2 Server-based Naming Authority		The authority component is preceded by a double slash ("//") and is
			terminated by the next slash ("/"), question-mark ("?"), or
			crosshatch ("#") character, or by the end of the URI.
	URI schemes that involve the direct use of an IP-based protocol to a		authority = [ userinfo "@" ] host [ ":" port ]
	specified server on the Internet use a common syntax for the server
	component of the URI's scheme-specific data:
	<userinfo>@<host>:<port>		The parts "<userinfo>@" and ":<port>" may be omitted.
	where <userinfo> may consist of a user name and, optionally,		Some schemes do not allow the userinfo and/or port sub-components.
	scheme-specific information about how to gain authorization to access		When presented with a URI that violates one or more scheme-specific
	the server. The parts "<userinfo>@" and ":<port>" may be omitted. If		restrictions, the scheme-specific URI resolution process should flag
	<host> is omitted, the default host is defined by the scheme-specific		the reference as an error rather than ignore the unused parts; doing
	semantics of the URI (e.g., the "file" URI scheme defaults to		so reduces the number of equivalent URIs and helps detect abuses of
	"localhost", whereas the "http" URI scheme does not allow host to be		the generic syntax that might indicate the URI has been constructed
	omitted).		to mislead the user (Section 7.5).
	server = [ [ userinfo "@" ] hostport ]		3.2.1 User Information
	The user information, if present, is followed by a commercial		The userinfo sub-component may consist of a user name and,
	at-sign "@".		optionally, scheme-specific information about how to gain
			authorization to access the server. The user information, if
			present, is followed by a commercial at-sign ("@") that delimits it
			from the host.
	userinfo = *( unreserved / escaped / ";" /		userinfo = *( unreserved / escaped / ";" /
	":" / "&" / "=" / "+" / "$" / "," )		":" / "&" / "=" / "+" / "$" / "," )
	Some URI schemes use the format "user:password" in the userinfo		Some URI schemes use the format "user:password" in the userinfo
	field. This practice is NOT RECOMMENDED, because the passing of		field. This practice is NOT RECOMMENDED, because the passing of
	authentication information in clear text has proven to be a security		authentication information in clear text has proven to be a security
	risk in almost every case where it has been used. Note also that		risk in almost every case where it has been used. Note also that
	userinfo which is crafted to look like a trusted domain name might be		userinfo might be crafted to look like a trusted domain name in order
	used to mislead users, as described in Section 7.5.		to mislead users, as described in Section 7.5.
	The server is identified by a network host --- as described by an		3.2.2 Host
	IPv6 literal encapsulated within square brackets, an IPv4 address in
	dotted-decimal form, or a domain name --- and an optional port
	number. The server's port, if any is required by the URI scheme, can
	be specified by a port number in decimal following the host and
	delimited from it by a colon (":") character. If no explicit port
	number is given, the default port number, as defined by the URI
	scheme, is assumed. The type of network port identified by the URI
	(e.g., TCP, UDP, SCTP, etc.) is defined by the scheme-specific
	semantics of the URI scheme.
	hostport = host [ ":" port ]		The host sub-component of authority is identified by an IPv6 literal
	host = IPv6reference / IPv4address / hostname		encapsulated within square brackets, an IPv4 address in
	port = *DIGIT		dotted-decimal form, or a domain name.
			host = [ IPv6reference / IPv4address / hostname ]
			If host is omitted, a default may be defined by the scheme-specific
			semantics of the URI. For example, the "file" URI scheme defaults to
			"localhost", whereas the "http" URI scheme does not allow host to be
			omitted.
			The production for host is ambiguous because it does not completely
			distinguish between an IPv4address and a hostname. Again, the
			"first-match-wins" algorithm applies: If host matches the production
			for IPv4address, then it should be considered an IPv4 address literal
			and not a hostname.
	A hostname takes the form described in Section 3 of [RFC1034] and		A hostname takes the form described in Section 3 of [RFC1034] and
	Section 2.1 of [RFC1123]: a sequence of domain labels separated by		Section 2.1 of [RFC1123]: a sequence of domain labels separated by
	".", each domain label starting and ending with an alphanumeric		".", each domain label starting and ending with an alphanumeric
	character and possibly also containing "-" characters. The rightmost		character and possibly also containing "-" characters. The rightmost
	domain label of a fully qualified domain name will never start with a		domain label of a fully qualified domain name may be followed by a
	digit, thus syntactically distinguishing domain names from IPv4		single "." if it is necessary to distinguish between the complete
	addresses, and may be followed by a single "." if it is necessary to		domain name and some local domain.
	distinguish between the complete domain name and any local domain.
	hostname = domainlabel qualified		hostname = domainlabel qualified
	qualified = *( "." domainlabel ) [ "." toplabel "." ]		qualified = *( "." domainlabel ) [ "." ]
	domainlabel = alphanum [ 0*61( alphanum | "-" ) alphanum ]		domainlabel = alphanum [ 0*61( alphanum / "-" ) alphanum ]
	toplabel = alpha [ 0*61( alphanum | "-" ) alphanum ]		alphanum = ALPHA / DIGIT
	alphanum = ALPHA / DIGIT
	A host identified by an IPv4 literal address is represented in		A host identified by an IPv4 literal address is represented in
	dotted-decimal notation (a sequence of four decimal numbers in the		dotted-decimal notation (a sequence of four decimal numbers in the
	range 0 to 255, separated by "."), as described in [RFC1123] by		range 0 to 255, separated by "."), as described in [RFC1123] by
	reference to [RFC0952]. Note that other forms of dotted notation may		reference to [RFC0952]. Note that other forms of dotted notation may
	be interpreted on some platforms, as described in Section 7.3, but		be interpreted on some platforms, as described in Section 7.3, but
	only the dotted-decimal form of four octets is allowed by this		only the dotted-decimal form of four octets is allowed by this
	grammar.		grammar.
	IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet		IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
	dec-octet = DIGIT / ; 0-9		dec-octet = DIGIT ; 0-9
	( %x31-39 DIGIT ) / ; 10-99		/ %x31-39 DIGIT ; 10-99
	( "1" 2DIGIT ) / ; 100-199		/ "1" 2DIGIT ; 100-199
	( "2" %x30-34 DIGIT ) / ; 200-249		/ "2" %x30-34 DIGIT ; 200-249
	( "25" %x30-35 ) ; 250-255		/ "25" %x30-35 ; 250-255
	A host identified by an IPv6 literal address [RFC2373] is		A host identified by an IPv6 literal address [RFC3513] is
	distinguished by enclosing the IPv6 literal within square-brakets		distinguished by enclosing the IPv6 literal within square-brackets
	("[" and "]"). This is the only place where square-bracket		("[" and "]"). This is the only place where square-bracket
	characters are allowed in the hierarchical URI syntax.		characters are allowed in the URI syntax.
	IPv6reference = "[" IPv6address "]"		IPv6reference = "[" IPv6address "]"
	IPv6address = ( 6( h4 ":" ) ls32 )		IPv6address = 6( h4 ":" ) ls32
	/ ( "::" 5( h4 ":" ) ls32 )		/ "::" 5( h4 ":" ) ls32
	/ ( [ h4 ] "::" 4( h4 ":" ) ls32 )		/ [ h4 ] "::" 4( h4 ":" ) ls32
	/ ( [ *1( h4 ":" ) h4 ] "::" 3( h4 ":" ) ls32 )		/ [ *1( h4 ":" ) h4 ] "::" 3( h4 ":" ) ls32
	/ ( [ *2( h4 ":" ) h4 ] "::" 2( h4 ":" ) ls32 )		/ [ *2( h4 ":" ) h4 ] "::" 2( h4 ":" ) ls32
	/ ( [ *3( h4 ":" ) h4 ] "::" h4 ":" ls32 )		/ [ *3( h4 ":" ) h4 ] "::" h4 ":" ls32
	/ ( [ *4( h4 ":" ) h4 ] "::" ls32 )		/ [ *4( h4 ":" ) h4 ] "::" ls32
	/ ( [ *5( h4 ":" ) h4 ] "::" h4 )		/ [ *5( h4 ":" ) h4 ] "::" h4
	/ ( [ *6( h4 ":" ) h4 ] "::" )		/ [ *6( h4 ":" ) h4 ] "::"
	ls32 = ( h4 ":" h4 ) / IPv4address		ls32 = ( h4 ":" h4 ) / IPv4address
	; least-significant 32 bits of address		; least-significant 32 bits of address
	h4 = 1*4HEXDIG		h4 = 1*4HEXDIG
	3.3 Path Component		The presence of host within a URI does not imply that the scheme
			requires access to the given host on the Internet. In many cases,
			the host syntax is used only for the sake of reusing the existing
			registration process created and deployed for DNS, thus obtaining a
			globally unique name without the cost of deploying another registry.
			However, such use comes with its own costs: domain name ownership may
			change over time for reasons not anticipated by the URI creator.
	The path component contains data, specific to the authority (or the		3.2.3 Port
	scheme if there is no authority component), identifying the resource
	within the scope of that scheme and authority.
	path = [ abs-path / opaque-part ]		The port sub-component of authority is designated by an optional
			port number in decimal following the host and delimited from it by a
			single colon (":") character.
			port = *DIGIT
			If port is omitted, a default may be defined by the scheme-specific
			semantics of the URI. Likewise, the type of network port designated
			by the port number (e.g., TCP, UDP, SCTP, etc.) is defined by the URI
			scheme. For example, the "http" URI scheme defines a default of TCP
			port 80.
			3.3 Path
			The path component contains hierarchical data that, along with data
			in the optional query (Section 3.4) component, serves to identify a
			resource within the scope of that URI's scheme and naming authority
			(if any). There is no specific "path" syntax production in the
			generic URI syntax. Instead, what we refer to as the URI path is
			that part of the parsed URI string matching either the abs-path or
			the rel-path production, since they are mutually exclusive for any
			given URI and can be parsed as a single component. The path is
			terminated by the first question-mark ("?") or crosshatch ("#")
			character, or by the end of the URI.
	path-segments = segment *( "/" segment )		path-segments = segment *( "/" segment )
	segment = *pchar		segment = *pchar
	pchar = unreserved / escaped / ";" /		pchar = unreserved / escaped / ";" /
	":" / "@" / "&" / "=" / "+" / "$" / ","		":" / "@" / "&" / "=" / "+" / "$" / ","
	The path may consist of a sequence of path segments separated by a		The path consists of a sequence of path segments separated by a slash
	single slash "/" character. Within a path segment, the characters "/		("/") character. A path is always defined for a URI, though the
	", ";", "=", and "?" are reserved. The semicolon (";") and equals		defined path may be empty (zero length) or opaque (not containing any
	("=") characters have the reserved purpose of delimiting parameters		"/" delimiters). For example, the URI <mailto:fred@example.com> has
	and parameter values within a path segment. However, parameters are		a path of "fred@example.com".
	not significant to the parsing of relative references.
	3.4 Query Component		Within a path segment, the semicolon (";") and equals ("=") reserved
			characters are often used for delimiting parameters and parameter
			values applicable to that segment. The comma (",") reserved
			character is often used for similar purposes. For example, one URI
			generator might use a segment like "name;v=1.1" to indicate a
			reference to version 1.1 of "name", whereas another might use a
			segment like "name,1.1" to indicate the same. Parameter types may be
			defined by scheme-specific semantics, but in most cases the meaning
			of a parameter is specific to the URI originator. Parameters are not
			significant to the parsing of relative references.
	The query component is a string of information to be interpreted by		The path segments "." and ".." are defined for relative reference
	the resource.		within the path name hierarchy. They are intended for use at the
			beginning of a relative path reference (Section 4.2) for indicating
			relative position within the hierarchical tree of names, with a
			similar effect to how they are used within some operating systems'
			file directory structure to indicate the current directory and parent
			directory, respectively. Unlike a file system, however, these
			dot-segments are only interpreted within the URI path hierarchy and
			must be removed as part of the URI normalization or resolution
			process, in accordance with the process described in Section 5.2.
	query = *( pchar / "/" / "?" )		3.4 Query
	Within a query component, the characters ";", "/", "?", ":", "@",		The query component contains non-hierarchical data that, along with
	"&", "=", "+", ",", and "$" are reserved.		data in the path (Section 3.3) component, serves to identify a
			resource within the scope of that URI's scheme and naming authority
			(if any). The query component is indicated by the first question-mark
			("?") character and terminated by a crosshatch ("#") character or by
			the end of the URI.
	4. URI References		query = *( pchar / "/" / "?" )
	The term "URI-reference" is used here to denote the common usage of		The characters slash ("/") and question-mark ("?") are allowed to
	a resource identifier. A URI reference may be absolute or relative,		represent data within the query component, but such use is
	and may have additional information attached in the form of a		discouraged; incorrect implementations of relative URI resolution
	fragment identifier. However, "the URI" that results from such a		often fail to distinguish them from hierarchical separators, thus
	reference includes only the absolute URI after the fragment		resulting in non-interoperable results while parsing relative
	identifier (if any) is removed and after any relative URI is resolved		references. However, since query components are often used to carry
	to its absolute form. Although it is possible to limit the		identifying information in the form of "key=value" pairs, and one
	discussion of URI syntax and semantics to that of the absolute		frequently used value is a reference to another URI, it is sometimes
	result, most usage of URI is within general URI references, and it is		better for usability to include those characters unescaped.
	impossible to obtain the URI from such a reference without also
	parsing the fragment and resolving the relative form.
	URI-reference = [ absolute-URI / relative-URI ] [ "#" fragment ]		3.5 Fragment
	Many protocol elements allow only the absolute form of a URI with an		The fragment identifier component allows indirect identification of
	optional fragment identifier.		a secondary resource by reference to a primary resource and
			additional identifying information that is selective within that
			resource. The identified secondary resource may be some portion or
			subset of the primary resource, some view on representations of the
			primary resource, or some other resource that is merely named within
			the primary resource. A fragment identifier component is indicated
			by the presence of a crosshatch ("#") character and terminated by the
			end of the URI string.
	absolute-URI-reference = absolute-URI [ "#" fragment ]		fragment = *( pchar / "/" / "?" )
	The syntax for a relative URI is a shortened form of that for an		The semantics of a fragment identifier are defined by the set of
	absolute URI, where some prefix of the URI is missing and certain		representations that might result from a retrieval action on the
	path components ("." and "..") have a special meaning when, and only		primary resource. Therefore, the format and interpretation of a
	when, interpreting a relative path. The relative URI syntax is		fragment identifier component is dependent on the media type
	defined in Section 5.		[RFC2046] of a potential retrieval result. Individual media types
			may define their own restrictions on, or structure within, the
			fragment identifier syntax for specifying different types of subsets,
			views, or external references that are identifiable as fragments by
			that media type. If the primary resource is represented by multiple
			media types, as is often the case for resources whose representation
			is selected based on attributes of the retrieval request, then
			interpretation of the given fragment identifier must be consistent
			across all of those media types in order for it to be viable as an
			identifier.
	4.1 Fragment Identifier		As with any URI, use of a fragment identifier component does not
			imply that a retrieval action will take place. A URI with a fragment
			identifier may be used to refer to the secondary resource without any
			implication that the primary resource is accessible. However, if
			that URI is used in a context that does call for retrieval and is not
			a same-document reference (Section 4.4), the fragment identifier is
			only valid as a reference if a retrieval action on the primary
			resource succeeds and results in a representation that defines the
			fragment.
	When a URI reference is used to perform a retrieval action on the		Fragment identifiers have a special role in information systems as
	identified resource, the optional fragment identifier, separated from		the primary form of client-side indirect referencing, allowing an
	the URI by a crosshatch ("#") character, consists of additional		author to specifically identify those aspects of an existing resource
	reference information to be interpreted by the user agent after the		that are only indirectly provided by the resource owner. As such,
	retrieval action has been successfully completed. As such, it is not		interpretation of the fragment identifier during a retrieval action
	part of a URI, but is often used in conjunction with a URI.		is performed solely by the user agent; the fragment identifier is not
			passed to other systems during the process of retrieval. Although
			this is often perceived to be a loss of information, particularly in
			regards to accurate redirection of references as content moves over
			time, it also serves to prevent information providers from denying
			reference authors the right to selectively refer to information
			within a resource.
	fragment = *( pchar / "/" / "?" )		The characters slash ("/") and question-mark ("?") are allowed to
			represent data within the fragment identifier, but such use is
			discouraged for the same reasons as described above for query.
	The semantics of a fragment identifier is a property of the data		4. Usage
	resulting from a retrieval action, regardless of the type of URI used
	in the reference. Therefore, the format and interpretation of
	fragment identifiers is dependent on the media type [RFC2046] of the
	retrieval result. The character restrictions described in Section 2
	for a URI also apply to the fragment in a URI-reference. Individual
	media types may define additional restrictions or structure within
	the fragment for specifying different types of "partial views" that
	can be identified within that media type.
	A fragment identifier is only meaningful when a URI reference is		When applications make reference to a URI, they do not always use the
	intended for retrieval and the result of that retrieval is a document		full form of reference defined by the "URI" syntax production. In
	for which the identified fragment is consistently defined.		order to save space and take advantage of hierarchical locality, many
			Internet protocol elements and media type formats allow an
			abbreviation of a URI, while others restrict the syntax to a
			particular form of URI. We define the most common forms of reference
			syntax in this specification because they impact and depend upon the
			design of the generic syntax, requiring a uniform parsing algorithm
			in order to be interpreted consistently.
	4.2 Same-document References		4.1 URI Reference
	A URI reference that does not contain a URI is a reference to the		The ABNF rule URI-reference is used to denote the most common usage
	current document. In other words, an empty URI reference within a		of a resource identifier.
	document is interpreted as a reference to the start of that document,
	and a reference containing only a fragment identifier is a reference
	to the identified fragment of that document. Traversal of such a
	reference should not result in an additional retrieval action.
	However, if the URI reference occurs in a context that is always
	intended to result in a new request, as in the case of HTML's FORM
	element [HTML], then an empty URI reference represents the base URI
	of the current document and should be replaced by that URI when
	transformed into a request.
	4.3 Parsing a URI Reference		URI-reference = URI / relative-URI
	A URI reference is typically parsed according to the four main		A URI-reference may be absolute or relative: if the reference
	components and fragment identifier in order to determine what		string's prefix matches the syntax of a scheme followed by its colon
	components are present and whether the reference is relative or		separator, then the reference is a URI rather than a relative-URI.
	absolute. The individual components are then parsed for their
	subparts and, if not opaque, to verify their validity.
	Although the BNF defines what is allowed in each component, it is		A URI-reference is typically parsed first into the five URI
	ambiguous in terms of differentiating between an authority component		components, in order to determine what components are present and
	and a path component that begins with two slash characters. The		whether the reference is relative or absolute, and then each
	greedy algorithm is used for disambiguation: the left-most matching		component is parsed for its subparts and their validation. The ABNF
	rule soaks up as much of the URI reference string as it is capable of		of URI-reference, along with the "first-match-wins" disambiguation
	matching. In other words, the authority component wins.		rule, is sufficient to define a validating parser for the generic
			syntax. Readers familiar with regular expressions should see
			Appendix B for an example of a non-validating URI-reference parser
			that will take any given string and extract the URI components.
	Readers familiar with regular expressions should see Appendix B for a		4.2 Relative URI
	concrete parsing example and test oracle.
	5. Relative URI References		A relative URI reference takes advantage of the hier-part syntax
			(Section 3) in order to express a reference that is relative to the
			name space of another hierarchical URI.
			relative-URI = hier-part [ "?" query ] [ "#" fragment ]
			The URI referred to by a relative URI reference is obtained by
			applying the relative resolution algorithm of Section 5.
			A relative reference that begins with two slash characters is termed
			a network-path reference; such references are rarely used. A relative
			reference that begins with a single slash character is termed an
			absolute-path reference. A relative reference that does not begin
			with a slash character is termed a relative-path reference.
			A path segment that contains a colon character (e.g., "this:that")
			cannot be used as the first segment of a relative-path reference
			because it might be mistaken for a scheme name. Such a segment must
			be preceded by a dot-segment (e.g., "./this:that") to make a
			relative-path reference.
			4.3 Absolute URI
			Some protocol elements allow only the absolute form of a URI without
			a fragment identifier. For example, defining the base URI for later
			use by relative references calls for an absolute-URI production that
			does not allow a fragment.
			absolute-URI = scheme ":" hier-part [ "?" query ]
			4.4 Same-document Reference
			When a URI reference occurring within a document or message refers to
			a URI that is, aside from its fragment component (if any), identical
			to the base URI (Section 5), that reference is called a
			"same-document" reference. The most frequent examples of
			same-document references are relative references that are empty or
			include only the crosshatch ("#") separator followed by a fragment
			identifier.
			When a same-document reference is dereferenced for the purpose of a
			retrieval action, the target of that reference is defined to be
			within that current document or message; the dereference should not
			result in a new retrieval.
			4.5 Suffix Reference
			The URI syntax is designed for unambiguous reference to resources and
			extensibility via the URI scheme. However, as URI identification and
			usage have become commonplace, traditional media (television, radio,
			newspapers, billboards, etc.) have increasingly used a suffix of the
			URI as a reference, consisting of only the authority and path
			portions of the URI, such as
			www.w3.org/Addressing/
			or simply the DNS hostname on its own. Such references are primarily
			intended for human interpretation rather than machine, with the
			assumption that context-based heuristics are sufficient to complete
			the URI (e.g., most hostnames beginning with "www" are likely to have
			a URI prefix of "http://"). Although there is no standard set of
			heuristics for disambiguating a URI suffix, many client
			implementations allow them to be entered by the user and
			heuristically resolved. It should be noted that such heuristics may
			change over time, particularly when new URI schemes are introduced.
			Since a URI suffix has the same syntax as a relative path reference,
			a suffix reference cannot be used in contexts where relative URIs are
			expected. This limits use of suffix references to those places where
			there is no defined base URI, such as dialog boxes and off-line
			advertisements.
			5. Relative Resolution
	It is often the case that a group or "tree" of documents has been		It is often the case that a group or "tree" of documents has been
	constructed to serve a common purpose; the vast majority of URIs in		constructed to serve a common purpose; the vast majority of URIs in
	these documents point to resources within the tree rather than		these documents point to resources within the tree rather than
	outside of it. Similarly, documents located at a particular site are		outside of it. Similarly, documents located at a particular site are
	much more likely to refer to other resources at that site than to		much more likely to refer to other resources at that site than to
	resources at remote sites.		resources at remote sites.
	Relative addressing of URIs allows document trees to be partially		Relative referencing of URIs allows document trees to be partially
	independent of their location and access scheme. For instance, it is		independent of their location and access scheme. For instance, it is
	possible for a single set of hypertext documents to be simultaneously		possible for a single set of hypertext documents to be simultaneously
	accessible and traversable via each of the "file", "http", and "ftp"		accessible and traversable via each of the "file", "http", and "ftp"
	schemes if the documents refer to each other using relative URIs.		schemes if the documents refer to each other using relative URIs.
	Furthermore, such document trees can be moved, as a whole, without		Furthermore, such document trees can be moved, as a whole, without
	changing any of the relative references. Experience within the WWW		changing any of the relative references. Experience within the WWW
	has demonstrated that the ability to perform relative referencing is		has demonstrated that the ability to perform relative referencing is
	necessary for the long-term usability of embedded URIs.		necessary for the long-term usability of embedded URIs.
	The relative URI syntax takes advantage of the <hier-part> syntax of
	<absolute-URI> (Section 3) in order to express a reference that is
	relative to the namespace of another hierarchical URI.
	relative-URI = [ net-path / abs-path / rel-path ] [ "?" query ]
	A relative reference beginning with two slash characters is termed a
	network-path reference, as defined by <net-path> in Section 3. Such
	references are rarely used.
	A relative reference beginning with a single slash character is
	termed an absolute-path reference, as defined by <abs-path> in
	Section 3.
	A relative reference that does not begin with a scheme name or a
	slash character is termed a relative-path reference.
	rel-path = rel-segment [ abs-path ]
	rel-segment = 1*( unreserved / escaped / ";" /
	"@" / "&" / "=" / "+" / "$" / "," )
	Within a relative-path reference, the complete path segments "." and
	".." have special meanings: "the current hierarchy level" and "the
	level above this hierarchy level", respectively. Although this is
	very similar to their use within Unix-based filesystems to indicate
	directory levels, these path components are only considered special
	when resolving a relative-path reference to its absolute form
	(Section 5.2).
	Authors should be aware that a path segment which contains a colon
	character cannot be used as the first segment of a relative URI path
	(e.g., "this:that"), because it would be mistaken for a scheme name.
	It is therefore necessary to precede such segments with other
	segments (e.g., "./this:that") in order for them to be referenced as
	a relative path.
	It is not necessary for all URI within a given scheme to be
	restricted to the <hier-part> syntax, since the hierarchical
	properties of that syntax are only necessary when a relative URI is
	used within a particular document. Documents can only make use of a
	relative URI when their base URI fits within the <hier-part> syntax.
	It is assumed that any document which contains a relative reference
	will also have a base URI that obeys the syntax. In other words, a
	relative URI cannot be used within a document that has an unsuitable
	base URI.
	Some URI schemes do not allow a hierarchical syntax matching the
	<hier-part> syntax, and thus cannot use relative references.
	5.1 Establishing a Base URI		5.1 Establishing a Base URI
	The term "relative URI" implies that there exists some absolute "base		The term "relative URI" implies that there exists some absolute "base
	URI" against which the relative reference is applied. Indeed, the		URI" against which the relative reference is applied. Indeed, the
	base URI is necessary to define the semantics of any relative URI		base URI is necessary to define the semantics of any relative URI
	reference; without it, a relative reference is meaningless. In order		reference; without it, a relative reference is meaningless. In order
	for relative URI to be usable within a document, the base URI of that		for relative URI to be usable within a document, the base URI of that
	document must be known to the parser.		document must be known to the parser.
			A document that contains relative references must have a base URI
			that contains a hierarchical path component. In other words, a
			relative-URI cannot be used within a document that has an unsuitable
			base URI. Some URI schemes do not allow a hierarchical path component
			and are thus restricted to full URI references.
			An authority component is not required for a URI scheme to make use
			of relative references. A base URI without an authority component
			implies that any relative reference will also be without an authority
			component.
	The base URI of a document can be established in one of four ways,		The base URI of a document can be established in one of four ways,
	listed below in order of precedence. The order of precedence can be		listed below in order of precedence. The order of precedence can be
	thought of in terms of layers, where the innermost defined base URI		thought of in terms of layers, where the innermost defined base URI
	has the highest precedence. This can be visualized graphically as:		has the highest precedence. This can be visualized graphically as:
	.----------------------------------------------------------.		.----------------------------------------------------------.
	| .----------------------------------------------------. |		| .----------------------------------------------------. |
	| | .----------------------------------------------. | |		| | .----------------------------------------------. | |
	| | | .----------------------------------------. | | |		| | | .----------------------------------------. | | |
	| | | | .----------------------------------. | | | |		| | | | .----------------------------------. | | | |
	skipping to change at page 24, line 42 ¶		skipping to change at page 26, line 37 ¶
	It is beyond the scope of this document to specify how, for each		It is beyond the scope of this document to specify how, for each
	media type, the base URI can be embedded. It is assumed that user		media type, the base URI can be embedded. It is assumed that user
	agents manipulating such media types will be able to obtain the		agents manipulating such media types will be able to obtain the
	appropriate syntax from that media type's specification. An example		appropriate syntax from that media type's specification. An example
	of how the base URI can be embedded in the Hypertext Markup Language		of how the base URI can be embedded in the Hypertext Markup Language
	(HTML) [HTML] is provided in Appendix D.		(HTML) [HTML] is provided in Appendix D.
	A mechanism for embedding the base URI within MIME container types		A mechanism for embedding the base URI within MIME container types
	(e.g., the message and multipart types) is defined by MHTML		(e.g., the message and multipart types) is defined by MHTML
	[RFC2110]. Protocols that do not use the MIME message header syntax,		[RFC2110]. Protocols that do not use the MIME message header syntax,
	but which do allow some form of tagged metainformation to be included		but do allow some form of tagged metadata to be included within
	within messages, may define their own syntax for defining the base		messages, may define their own syntax for defining the base URI as
	URI as part of a message.		part of a message.
	5.1.2 Base URI from the Encapsulating Entity		5.1.2 Base URI from the Encapsulating Entity
	If no base URI is embedded, the base URI of a document is defined by		If no base URI is embedded, the base URI of a document is defined by
	the document's retrieval context. For a document that is enclosed		the document's retrieval context. For a document that is enclosed
	within another entity (such as a message or another document), the		within another entity (such as a message or another document), the
	retrieval context is that entity; thus, the default base URI of the		retrieval context is that entity; thus, the default base URI of the
	document is the base URI of the entity in which the document is		document is the base URI of the entity in which the document is
	encapsulated.		encapsulated.
	skipping to change at page 25, line 18 ¶		skipping to change at page 27, line 16 ¶
	If no base URI is embedded and the document is not encapsulated		If no base URI is embedded and the document is not encapsulated
	within some other entity (e.g., the top level of a composite entity),		within some other entity (e.g., the top level of a composite entity),
	then, if a URI was used to retrieve the base document, that URI shall		then, if a URI was used to retrieve the base document, that URI shall
	be considered the base URI. Note that if the retrieval was the		be considered the base URI. Note that if the retrieval was the
	result of a redirected request, the last URI used (i.e., that which		result of a redirected request, the last URI used (i.e., that which
	resulted in the actual retrieval of the document) is the base URI.		resulted in the actual retrieval of the document) is the base URI.
	5.1.4 Default Base URI		5.1.4 Default Base URI
	If none of the conditions described in Sections 5.1.1--5.1.3 apply,		If none of the conditions described in above apply, then the base URI
	then the base URI is defined by the context of the application. Since		is defined by the context of the application. Since this definition
	this definition is necessarily application-dependent, failing to		is necessarily application-dependent, failing to define the base URI
	define the base URI using one of the other methods may result in the		using one of the other methods may result in the same content being
	same content being interpreted differently by different types of		interpreted differently by different types of application.
	application.
	It is the responsibility of the distributor(s) of a document		It is the responsibility of the distributor(s) of a document
	containing a relative URI to ensure that the base URI for that		containing a relative URI to ensure that the base URI for that
	document can be established. It must be emphasized that a relative		document can be established. It must be emphasized that a relative
	URI cannot be used reliably in situations where the document's base		URI cannot be used reliably in situations where the document's base
	URI is not well-defined.		URI is not well-defined.
	5.2 Resolving Relative References to Absolute Form		5.2 Obtaining the Referenced URI
	This section describes an example algorithm for resolving URI		This section describes an example algorithm for resolving URI
	references that might be relative to a given base URI. The algorithm		references that might be relative to a given base URI. The algorithm
	is intended to provide a definitive result that can be used to test		is intended to provide a definitive result that can be used to test
	the output of other implementations. Implementation of the algorithm		the output of other implementations. Implementation of the algorithm
	itself is not required, but the result given by an implementation		itself is not required, but the result given by an implementation
	must match the result that would be given by this algorithm.		must match the result that would be given by this algorithm.
	The base URI is established according to the rules of Section 5.1 and		The base URI (Base) is established according to the rules of Section
	parsed into the four main components as described in Section 3. Note		5.1 and parsed into the five main components described in Section 3.
	that only the scheme component is required to be present in the base		Note that only the scheme component is required to be present in the
	URI; the other components may be empty or undefined. A component is		base URI; the other components may be empty or undefined. A
	undefined if its preceding separator does not appear in the URI		component is undefined if its preceding separator does not appear in
	reference; the path component is never undefined, though it may be		the URI reference; the path component is never undefined, though it
	empty. The base URI's query component is not used by the resolution		may be empty.
	algorithm and may be discarded.
	For each URI reference (R), the following pseudocode describes an		For each URI reference (R), the following pseudocode describes an
	algorithm for transforming R into its target (T), which is either an		algorithm for transforming R into its target URI (T):
	absolute URI or the current document, and R's optional fragment:
	(R.scheme, R.authority, R.path, R.query, fragment) = parse(R);		(R.scheme, R.authority, R.path, R.query, R.fragment) = parse(R);
	-- The URI reference is parsed into the four components and		-- The URI reference is parsed into the five URI components
	-- fragment identifier, as described in Section 4.3.
	if ((not validating) and (R.scheme == Base.scheme)) then		if ((not validating) and (R.scheme == Base.scheme)) then
	-- A non-validating parser may ignore a scheme in the		-- A non-validating parser may ignore a scheme in the
	-- reference if it is identical to the base URI's scheme.		-- reference if it is identical to the base URI's scheme.
	undefine(R.scheme);		undefine(R.scheme);
	endif;		endif;
	if defined(R.scheme) then		if defined(R.scheme) then
	T.scheme = R.scheme;		T.scheme = R.scheme;
	T.authority = R.authority;		T.authority = R.authority;
	T.path = R.path;		T.path = R.path;
	T.query = R.query;		T.query = R.query;
	else		else
	if defined(R.authority) then		if defined(R.authority) then
	T.authority = R.authority;		T.authority = R.authority;
	T.path = R.path;		T.path = R.path;
	T.query = R.query;		T.query = R.query;
	else		else
	if (R.path == "") then		if (R.path == "") then
			T.path = Base.path;
	if defined(R.query) then		if defined(R.query) then
	T.path = Base.path;
	T.query = R.query;		T.query = R.query;
	else		else
	-- An empty reference refers to the current document		T.query = Base.query;
	return (current-document, fragment);
	endif;		endif;
	else		else
	if (R.path starts-with "/") then		if (R.path starts-with "/") then
	T.path = R.path;		T.path = R.path;
	else		else
	T.path = merge(Base.path, R.path);		T.path = merge(Base.path, R.path);
	endif;		endif;
	T.query = R.query;		T.query = R.query;
	endif;		endif;
	T.authority = Base.authority;		T.authority = Base.authority;
	endif;		endif;
	T.scheme = Base.scheme;		T.scheme = Base.scheme;
	endif;		endif;
	return (T, fragment);		T.fragment = R.fragment;
	The pseudocode above refers to a merge routine for merging a		The pseudocode above refers to a merge routine for merging a
	relative-path reference with the path of the base URI to obtain the		relative-path reference with the path of the base URI to obtain the
	target path. Although there are many ways to do this, we will		target path. Although there are many ways to do this, we will
	describe a simple method using a separate string buffer:		describe a simple method using a separate string buffer:
	1. All but the last segment of the base URI's path component is		1. All but the last segment of the base URI's path component is
	copied to the buffer. In other words, any characters after the		copied to the buffer. In other words, any characters after the
	last (right-most) slash character, if any, are excluded. If the		last (right-most) slash character, if any, are excluded. If the
	base URI's path component is the empty string, then a single		base URI's path component is the empty string, then a single
	skipping to change at page 27, line 32 ¶		skipping to change at page 29, line 26 ¶
	removing the leftmost matching pattern on each iteration, until		removing the leftmost matching pattern on each iteration, until
	no matching pattern remains.		no matching pattern remains.
	6. If the buffer string ends with "<segment>/..", where <segment> is		6. If the buffer string ends with "<segment>/..", where <segment> is
	a complete path segment not equal to "..", that "<segment>/.." is		a complete path segment not equal to "..", that "<segment>/.." is
	removed.		removed.
	7. If the resulting buffer string still begins with one or more		7. If the resulting buffer string still begins with one or more
	complete path segments of "..", then the reference is considered		complete path segments of "..", then the reference is considered
	to be in error. Implementations may handle this error by		to be in error. Implementations may handle this error by
	retaining these components in the resolved path (i.e., treating		removing them from the resolved path (i.e., discarding relative
	them as part of the final URI), by removing them from the		levels above the root) or by avoiding traversal of the reference.
	resolved path (i.e., discarding relative levels above the root),
	or by avoiding traversal of the reference.
	8. The remaining buffer string is the target URI's path component.		8. The remaining buffer string is the target URI's path component.
	Some systems may find it more efficient to implement the merge		Some systems may find it more efficient to implement the merge
	algorithm as a pair of path segment stacks being merged, rather than		algorithm as a pair of path segment stacks being merged, rather than
	as a series of string pattern replacements.		as a series of string pattern replacements.
	Note: Some WWW client applications will fail to separate the		Note: Some WWW client applications will fail to separate the
	reference's query component from its path component before merging		reference's query component from its path component before merging
	the base and reference paths. This may result in a loss of		the base and reference paths. This may result in a loss of
	information if the query component contains the strings "/../" or		information if the query component contains the strings "/../" or
	"/./".		"/./".
	The resulting target URI components and fragment can be recombined to		5.3 Recomposition of a Parsed URI
	provide the absolute form of the URI reference. Using pseudocode,
	this would be:		Parsed URI components can be recombined to obtain the referenced URI.
			Using pseudocode, this would be:
	result = ""		result = ""
	if defined(T.scheme) then		if defined(T.scheme) then
	append T.scheme to result;		append T.scheme to result;
	append ":" to result;		append ":" to result;
	endif;		endif;
	if defined(T.authority) then		if defined(T.authority) then
	append "//" to result;		append "//" to result;
	append T.authority to result;		append T.authority to result;
	endif;		endif;
	append T.path to result;		append T.path to result;
	if defined(T.query) then		if defined(T.query) then
	append "?" to result;		append "?" to result;
	append T.query to result;		append T.query to result;
	endif;		endif;
	if defined(fragment) then		if defined(fragment) then
	append "#" to result;		append "#" to result;
	append fragment to result;		append fragment to result;
	endif;		endif;
	return result;		return result;
	Note that we must be careful to preserve the distinction between a		Note that we are careful to preserve the distinction between a
	component that is undefined, meaning that its separator was not		component that is undefined, meaning that its separator was not
	present in the reference, and a component that is empty, meaning that		present in the reference, and a component that is empty, meaning that
	the separator was present and was immediately followed by the next		the separator was present and was immediately followed by the next
	component separator or the end of the reference.		component separator or the end of the reference.
	Resolution examples are provided in Appendix C.		5.4 Examples of Relative Resolution
	6. URI Normalization and Comparison		Within an object with a well-defined base URI of
			http://a/b/c/d;p?q
			a relative URI reference would be resolved as follows:
			5.4.1 Normal Examples
			"g:h" = "g:h"
			"g" = "http://a/b/c/g"
			"./g" = "http://a/b/c/g"
			"g/" = "http://a/b/c/g/"
			"/g" = "http://a/g"
			"//g" = "http://g"
			"?y" = "http://a/b/c/d;p?y"
			"g?y" = "http://a/b/c/g?y"
			"#s" = "http://a/b/c/d;p?q#s"
			"g#s" = "http://a/b/c/g#s"
			"g?y#s" = "http://a/b/c/g?y#s"
			";x" = "http://a/b/c/;x"
			"g;x" = "http://a/b/c/g;x"
			"g;x?y#s" = "http://a/b/c/g;x?y#s"
			"." = "http://a/b/c/"
			"./" = "http://a/b/c/"
			".." = "http://a/b/"
			"../" = "http://a/b/"
			"../g" = "http://a/b/g"
			"../.." = "http://a/"
			"../../" = "http://a/"
			"../../g" = "http://a/g"
			5.4.2 Abnormal Examples
			Although the following abnormal examples are unlikely to occur in
			normal practice, all URI parsers should be capable of resolving them
			consistently. Each example uses the same base as above.
			An empty reference refers to the current base URI.
			"" = "http://a/b/c/d;p?q"
			Parsers must be careful in handling the case where there are more
			relative path ".." segments than there are hierarchical levels in the
			base URI's path. Note that the ".." syntax cannot be used to change
			the authority component of a URI.
			"../../../g" = "http://a/g"
			"../../../../g" = "http://a/g"
			Similarly, parsers should remove the dot-segments "." and ".." when
			they are complete components of a path, but not when they are only
			part of a segment.
			"/./g" = "http://a/g"
			"/../g" = "http://a/g"
			"g." = "http://a/b/c/g."
			".g" = "http://a/b/c/.g"
			"g.." = "http://a/b/c/g.."
			"..g" = "http://a/b/c/..g"
			Less likely are cases where the relative URI uses unnecessary or
			nonsensical forms of the "." and ".." complete path segments.
			"./../g" = "http://a/b/g"
			"./g/." = "http://a/b/c/g/"
			"g/./h" = "http://a/b/c/g/h"
			"g/../h" = "http://a/b/c/h"
			"g;x=1/./y" = "http://a/b/c/g;x=1/y"
			"g;x=1/../y" = "http://a/b/c/y"
			Some applications fail to separate the reference's query and/or
			fragment components from a relative path before merging it with the
			base path. This error is rarely noticed, since typical usage of a
			fragment never includes the hierarchy ("/") character, and the query
			component is not normally used within relative references.
			"g?y/./x" = "http://a/b/c/g?y/./x"
			"g?y/../x" = "http://a/b/c/g?y/../x"
			"g#s/./x" = "http://a/b/c/g#s/./x"
			"g#s/../x" = "http://a/b/c/g#s/../x"
			Some parsers allow the scheme name to be present in a relative URI if
			it is the same as the base URI scheme. This is considered to be a
			loophole in prior specifications of partial URI [RFC1630]. Its use
			should be avoided, but is allowed for backward compatibility.
			"http:g" = "http:g" ; for validating parsers
			/ "http://a/b/c/g" ; for backward compatibility
			6. Normalization and Comparison
	One of the most common operations on URIs is simple comparison:		One of the most common operations on URIs is simple comparison:
	determining if two URIs are equivalent without using the URIs to		determining if two URIs are equivalent without using the URIs to
	access their respective resource(s). A comparison is performed every		access their respective resource(s). A comparison is performed every
	time a response cache is accessed, a browser checks its history to		time a response cache is accessed, a browser checks its history to
	color a link, or an XML parser processes tags within a namespace.		color a link, or an XML parser processes tags within a namespace.
	Extensive normalization prior to comparison of URIs is often used by		Extensive normalization prior to comparison of URIs is often used by
	spiders and indexing engines to prune a search space or reduce		spiders and indexing engines to prune a search space or reduce
	duplication of request actions and response storage.		duplication of request actions and response storage.
	URI comparison is performed in respect to some particular purpose,		URI comparison is performed in respect to some particular purpose,
	and software with differing purposes will often be subject to		and software with differing purposes will often be subject to
	differing design trade-offs in regards to how much effort should be		differing design trade-offs in regards to how much effort should be
	spent in reducing duplicate identifiers. This section describes a		spent in reducing duplicate identifiers. This section describes a
	variety of methods that may be used to compare URIs, the trade-offs		variety of methods that may be used to compare URIs, the trade-offs
	between them, and the types of applications that might use them.		between them, and the types of applications that might use them.
	6.1 URI Equivalence		6.1 Equivalence
	Since URIs exist to identify resources, presumably they should be		Since URIs exist to identify resources, presumably they should be
	considered equivalent when they identify the same resource. However,		considered equivalent when they identify the same resource. However,
	such a definition of equivalence is not of much practical use, since		such a definition of equivalence is not of much practical use, since
	there is no way for software to compare two resources without		there is no way for software to compare two resources without
	knowledge of their origin. For this reason, determination of		knowledge of their origin. For this reason, determination of
	equivalence or difference of URIs is based on string comparison,		equivalence or difference of URIs is based on string comparison,
	perhaps augmented by reference to additional rules provided by URI		perhaps augmented by reference to additional rules provided by URI
	scheme definitions. We use the terms "different" and "equivalent" to		scheme definitions. We use the terms "different" and "equivalent" to
	describe the possible outcomes of such comparisons, but there are		describe the possible outcomes of such comparisons, but there are
	skipping to change at page 29, line 46 ¶		skipping to change at page 33, line 46 ¶
	Even though it is possible to determine that two URIs are equivalent,		Even though it is possible to determine that two URIs are equivalent,
	it is never possible to be sure that two URIs identify different		it is never possible to be sure that two URIs identify different
	resources. Therefore, comparison methods are designed to minimize		resources. Therefore, comparison methods are designed to minimize
	false negatives while strictly avoiding false positives.		false negatives while strictly avoiding false positives.
	In testing for equivalence, it is generally unwise to directly		In testing for equivalence, it is generally unwise to directly
	compare relative URI references; they should be converted to their		compare relative URI references; they should be converted to their
	absolute forms before comparison. Furthermore, when URI references		absolute forms before comparison. Furthermore, when URI references
	are being compared for the purpose of selecting (or avoiding) a		are being compared for the purpose of selecting (or avoiding) a
	network action, such as retrieval of a representation, it is often		network action, such as retrieval of a representation, it is often
	necessary to separate fragment identifiers from the URIs prior to		necessary to remove fragment identifiers from the URIs prior to
	comparison.		comparison.
	6.2 Comparison Ladder		6.2 Comparison Ladder
	A variety of methods are used in practice to test URI equivalence.		A variety of methods are used in practice to test URI equivalence.
	These methods fall into a range, distinguished by the amount of		These methods fall into a range, distinguished by the amount of
	processing required and the degree to which the probability of false		processing required and the degree to which the probability of false
	negatives is reduced. As noted above, false negatives cannot in		negatives is reduced. As noted above, false negatives cannot in
	principle be eliminated. In practice, their probability can be		principle be eliminated. In practice, their probability can be
	reduced, but this reduction requires more processing and is not		reduced, but this reduction requires more processing and is not
	skipping to change at page 30, line 29 ¶		skipping to change at page 34, line 29 ¶
	is safe to conclude that they are equivalent. This type of		is safe to conclude that they are equivalent. This type of
	equivalence test has very low computational cost and is in wide use		equivalence test has very low computational cost and is in wide use
	in a variety of applications, particularly in the domain of parsing.		in a variety of applications, particularly in the domain of parsing.
	Testing strings for equivalence requires some basic precautions. This		Testing strings for equivalence requires some basic precautions. This
	procedure is often referred to as "bit-for-bit" or "byte-for-byte"		procedure is often referred to as "bit-for-bit" or "byte-for-byte"
	comparison, which is potentially misleading. Testing of strings for		comparison, which is potentially misleading. Testing of strings for
	equality is normally based on pairwise comparison of the characters		equality is normally based on pairwise comparison of the characters
	that make up the strings, starting from the first and proceeding		that make up the strings, starting from the first and proceeding
	until both strings are exhausted and all characters found to be		until both strings are exhausted and all characters found to be
	equal, or a pair of characters compares unequal or one of the strings		equal, a pair of characters compares unequal, or one of the strings
	is exhausted before the other.		is exhausted before the other.
	Such character comparisons require that each pair of characters be		Such character comparisons require that each pair of characters be
	put in comparable form. For example, should one URI be stored in a		put in comparable form. For example, should one URI be stored in a
	byte array in EBCDIC encoding, and the second be in a Java String		byte array in EBCDIC encoding, and the second be in a Java String
	object, bit-for-bit comparisons applied naively will produce both		object, bit-for-bit comparisons applied naively will produce both
	false-positive and false-negative errors. Thus, in principle, it is		false-positive and false-negative errors. Thus, in principle, it is
	better to speak of equality on a character-for-character rather than		better to speak of equality on a character-for-character rather than
	byte-for-byte or bit-for-bit basis.		byte-for-byte or bit-for-bit basis.
	Unicode defines a character as being identified by number		Unicode defines a character as being identified by number
	("codepoint") with an associated bundle of visual and other		("codepoint") with an associated bundle of visual and other
	semantics. At the software level, it is not practical to compare		semantics. At the software level, it is not practical to compare
	semantic bundles, so in practical terms, character-by-character		semantic bundles, so in practical terms, character-by-character
	comparisons are done codepoint-by-codepoint.		comparisons are done codepoint-by-codepoint.
	6.2.2 Syntax-based Normalization		6.2.2 Syntax-based Normalization
	Software may use logic based on the definitions provided by this		Software may use logic based on the definitions provided by this
	specification to reduce the probability of false negatives. Such		specification to reduce the probability of false negatives. Such
	processing is (moderately) higher in cost than		processing is moderately higher in cost than character-for-character
	character-for-character string comparison. For example, an		string comparison. For example, an application using this approach
	application using this approach could reasonably consider the		could reasonably consider the following two URIs equivalent:
	following two URIs equivalent:
	example://a/b/c/%7A		example://a/b/c/%7A
	eXAMPLE://a/./b/../b/c/%7a		eXAMPLE://a/./b/../b/c/%7a
	Web user agents, such as browsers, typically apply this type of URI		Web user agents, such as browsers, typically apply this type of URI
	normalization when determining whether a cached response is		normalization when determining whether a cached response is
	available. Syntax-based normalization includes such techniques as		available. Syntax-based normalization includes such techniques as
	case normalization, escape normalization, and removal of leftover		case normalization, escape normalization, and removal of leftover
	relative path segments.		relative path segments.
	6.2.2.1 Case Normalization		6.2.2.1 Case Normalization
	When a URI scheme uses elements of the common syntax, it will also		When a URI scheme uses components of the generic syntax, it will also
	use the common syntax equivalence rules, namely that the scheme and		use the common syntax equivalence rules, namely that the scheme and
	hostname are case insensitive and therefore can be normailized to		hostname are case insensitive and therefore can be normalized to
	lowercase. For example, the URI <HTTP://www.EXAMPLE.com/> is		lowercase. For example, the URI <HTTP://www.EXAMPLE.com/> is
	equivalent to <http://www.example.com/>.		equivalent to <http://www.example.com/>.
	6.2.2.2 Escape Normalization		6.2.2.2 Escape Normalization
	The %-escape mechanism described in Section 2.4 is a frequent source		The percent-escape mechanism described in Section 2.4 is a frequent
	of variance among otherwise identical URIs. One cause is the choice		source of variance among otherwise identical URIs. One cause is the
	of upper-case or lower-case letters for the hexadecimal digits within		choice of uppercase or lowercase letters for the hexadecimal digits
	the escape sequence (e.g., "%3a" versus "%3A"). Such sequences are		within the escape sequence (e.g., "%3a" versus "%3A"). Such sequences
	always equivalent; for the sake of uniformity, URI generators and		are always equivalent; for the sake of uniformity, URI generators and
	normalizers are strongly encouraged to use upper-case letters for the		normalizers are strongly encouraged to use uppercase letters for the
	hex digits A-F.		hex digits A-F.
	Only characters that are excluded from or reserved within the URI		Only characters that are excluded from or reserved within the URI
	syntax must be escaped when used as data. However, some URI		syntax must be escaped when used as data. However, some URI
	generators go beyond that and escape characters that do not require		generators go beyond that and escape characters that do not require
	escaping, resulting in URIs that are equivalent to their unescaped		escaping, resulting in URIs that are equivalent to their unescaped
	counterparts. Such URIs can be normalized by unescaping sequences		counterparts. Such URIs can be normalized by unescaping sequences
	that represent the unreserved characters, as described in Section		that represent the unreserved characters, as described in Section
	2.3.		2.3.
	skipping to change at page 32, line 25 ¶		skipping to change at page 36, line 24 ¶
	the probability of false negatives. For example, Web spiders that		the probability of false negatives. For example, Web spiders that
	populate most large search engines would consider the following two		populate most large search engines would consider the following two
	URIs to be equivalent:		URIs to be equivalent:
	http://example.com/		http://example.com/
	http://example.com:80/		http://example.com:80/
	This behavior is based on the rules provided by the syntax and		This behavior is based on the rules provided by the syntax and
	semantics of the "http" URI scheme, which defines an empty port		semantics of the "http" URI scheme, which defines an empty port
	component as being equivalent to the default TCP port for HTTP (port		component as being equivalent to the default TCP port for HTTP (port
	80). In general, a URI scheme that uses the generic syntax of		80). In general, a URI scheme that uses the generic syntax for
	hostport is defined such that a URI with an explicit ":port", where		authority is defined such that a URI with an explicit ":port", where
	the port is the default for the scheme, is equivalent to one where		the port is the default for the scheme, is equivalent to one where
	the port is elided.		the port is elided.
	6.2.4 Protocol-based Normalization		6.2.4 Protocol-based Normalization
	Web spiders, for which substantial effort to reduce the incidence of		Web spiders, for which substantial effort to reduce the incidence of
	false negatives is often cost-effective, are observed to implement		false negatives is often cost-effective, are observed to implement
	even more aggressive techniques in URI comparison. For example, if		even more aggressive techniques in URI comparison. For example, if
	they observe that a URI such as		they observe that a URI such as
	http://example.com/data		http://example.com/data
	redirects to		redirects to
	http://example.com/data/		http://example.com/data/
	they will likely regard the two as equivalent in the future.		they will likely regard the two as equivalent in the future.
	Obviously, this kind of technique is only appropriate in special		Obviously, this kind of technique is only appropriate in special
	situations.		situations.
	6.3 Good Practice When Using URIs		6.3 Canonical Form
	It is in the best interests of everyone to avoid false-negatives in		It is in the best interests of everyone to avoid false-negatives in
	comparing URIs, and to only require the minimum amount of software		comparing URIs and to minimize the amount of software processing for
	processing for such comparisons. Those who generate and make		such comparisons. Those who generate and make reference to URIs can
	reference to URIs can reduce the cost of processing and the risk of		reduce the cost of processing and the risk of false negatives by
	false negatives by consistently providing them in a form that is		consistently providing them in a form that is reasonably canonical
	reasonably canonical with respect to their scheme. Specifically:		with respect to their scheme. Specifically:
	Always provide the URI scheme in lower-case characters.
	Always provide the hostname, if any, in lower-case characters.		Always provide the URI scheme in lowercase characters.
	Only perform %-escaping where it is essential.		Always provide the hostname, if any, in lowercase characters.
	Always use upper-case A-through-F characters when %-escaping.		Only perform percent-escaping where it is essential.
	Use the UTF-8 character-to-octet mapping, whenever possible.		Always use uppercase A-through-F characters when percent-escaping.
	Prevent /./ and /../ from appearing in absolute URI paths.		Prevent /./ and /../ from appearing in non-relative URI paths.
	The choices listed above are motivated by observations that a high		The good practices listed above are motivated by observations that a
	proportion of deployed software already use these techniques in		high proportion of deployed software use these techniques for the
	practice for the purposes of normalization.		purposes of normalization.
	7. Security Considerations		7. Security Considerations
	A URI does not in itself pose a security threat. However, since URIs		A URI does not in itself pose a security threat. However, since URIs
	are often used to provide a compact set of instructions for access to		are often used to provide a compact set of instructions for access to
	network resources, care must be taken to properly interpret the data		network resources, care must be taken to properly interpret the data
	within a URI, to prevent that data from causing unintended access,		within a URI, to prevent that data from causing unintended access,
	and to avoid including data that should not be revealed in plain		and to avoid including data that should not be revealed in plain
	text.		text.
	7.1 Reliability and Consistency		7.1 Reliability and Consistency
	There is no guarantee that, having once used a given URI to retrieve		There is no guarantee that, having once used a given URI to retrieve
	some information, that the same information will be retievable by		some information, that the same information will be retrievable by
	that URI in the future. Nor is there any guarantee that the		that URI in the future. Nor is there any guarantee that the
	information retrievable via that URI in the future will be observably		information retrievable via that URI in the future will be observably
	similar to that retrieved in the past. The URI syntax does not		similar to that retrieved in the past. The URI syntax does not
	constrain how a given scheme or authority apportions its namespace or		constrain how a given scheme or authority apportions its name space
	maintains it over time. Such a guarantee can only be obtained from		or maintains it over time. Such a guarantee can only be obtained
	the person(s) controlling that namespace and the resource in		from the person(s) controlling that name space and the resource in
	question. A specific URI scheme may define additional semantics,		question. A specific URI scheme may define additional semantics,
	such as name persistence, if those semantics are required of all		such as name persistence, if those semantics are required of all
	naming authorities for that scheme.		naming authorities for that scheme.
	7.2 Malicious Construction		7.2 Malicious Construction
	It is sometimes possible to construct a URI such that an attempt to		It is sometimes possible to construct a URI such that an attempt to
	perform a seemingly harmless, idempotent operation, such as the		perform a seemingly harmless, idempotent operation, such as the
	retrieval of a representation associated with a resource, will in		retrieval of a representation, will in fact cause a possibly damaging
	fact cause a possibly damaging remote operation to occur. The unsafe		remote operation to occur. The unsafe URI is typically constructed
	URI is typically constructed by specifying a port number other than		by specifying a port number other than that reserved for the network
	that reserved for the network protocol in question. The client		protocol in question. The client unwittingly contacts a site that is
	unwittingly contacts a site that is in fact running a different		running a different protocol service. The content of the URI
	protocol. The content of the URI contains instructions that, when		contains instructions that, when interpreted according to this other
	interpreted according to this other protocol, cause an unexpected		protocol, cause an unexpected operation. An example has been the use
	operation. An example has been the use of a gopher URI to cause an		of a gopher URI to cause an unintended or impersonating message to be
	unintended or impersonating message to be sent via a SMTP server.		sent via a SMTP server.
	Caution should be used when using any URI that specifies a TCP port		Caution should be used when dereferencing a URI that specifies a TCP
	number other than the default for the protocol, especially when it is		port number other than the default for the scheme, especially when it
	a number within the reserved space.		is a number within the reserved space.
	Care should be taken when a URI contains escaped delimiters for a		Care should be taken when a URI contains escaped delimiters for a
	given protocol (for example, CR and LF characters for telnet		given protocol (for example, CR and LF characters for telnet
	protocols) that these are not unescaped before transmission. This		protocols) that these octets are not unescaped before transmission.
	might violate the protocol, but avoids the potential for such		This might violate the protocol, but avoids the potential for such
	characters to be used to simulate an extra operation or parameter in		characters to be used to simulate an extra operation or parameter in
	that protocol, which might lead to an unexpected and possibly harmful		that protocol which might lead to an unexpected and possibly harmful
	remote operation being performed.		remote operation being performed.
	7.3 Rare IP Address Formats		7.3 Rare IP Address Formats
	Although the URI syntax for IPv4address only allows the common,		Although the URI syntax for IPv4address only allows the common,
	dotted-decimal form of IPv4 address literal, many implementations		dotted-decimal form of IPv4 address literal, many implementations
	that process URIs make use of platform-dependent system routines,		that process URIs make use of platform-dependent system routines,
	such as gethostbyname() and inet_aton(), to translate the string		such as gethostbyname() and inet_aton(), to translate the string
	literal to an actual IP address. Unfortunately, such system routines		literal to an actual IP address. Unfortunately, such system routines
	often allow and process a much larger set of formats than those		often allow and process a much larger set of formats than those
	skipping to change at page 36, line 15 ¶		skipping to change at page 40, line 5 ¶
	7.5 Semantic Attacks		7.5 Semantic Attacks
	Because the userinfo component is rarely used and appears before the		Because the userinfo component is rarely used and appears before the
	hostname in the authority component, it can be used to construct a		hostname in the authority component, it can be used to construct a
	URI that is intended to mislead a human user by appearing to identify		URI that is intended to mislead a human user by appearing to identify
	one (trusted) naming authority while actually identifying a different		one (trusted) naming authority while actually identifying a different
	authority hidden behind the noise. For example		authority hidden behind the noise. For example
	http://www.example.com&story=breaking_news@10.0.0.1/top_story.htm		http://www.example.com&story=breaking_news@10.0.0.1/top_story.htm
	might lead a human user to assume that the authority is		might lead a human user to assume that the host is 'www.example.com',
	'www.example.com', whereas it is actually '10.0.0.1'. Note that the		whereas it is actually '10.0.0.1'. Note that the misleading userinfo
	misleading userinfo could be much longer than the example above.		could be much longer than the example above.
	A misleading URI, such as the one above, is an attack on the user's		A misleading URI, such as the one above, is an attack on the user's
	preconceived notions about the meaning of a URI, rather than an		preconceived notions about the meaning of a URI, rather than an
	attack on the software itself. User agents may be able to reduce the		attack on the software itself. User agents may be able to reduce the
	impact of such attacks by visually distinguishing the various		impact of such attacks by visually distinguishing the various
	components of the URI when rendered, such as by using a different		components of the URI when rendered, such as by using a different
	color or tone to render userinfo if any is present, though there is		color or tone to render userinfo if any is present, though there is
	no general panacea. More information on URI-based semantic attacks		no general panacea. More information on URI-based semantic attacks
	can be found in [Siedzik].		can be found in [Siedzik].
	8. Acknowledgements		8. Acknowledgments
	This document is derived from RFC 2396 [RFC2396], RFC 1808 [RFC1808],		This document is derived from RFC 2396 [RFC2396], RFC 1808 [RFC1808],
	and RFC 1738 [RFC1738]; the acknowledgements in those specifications		and RFC 1738 [RFC1738]; the acknowledgments in those specifications
	still apply. It also incorporates the update (with corrections) for		still apply. It also incorporates the update (with corrections) for
	IPv6 literals in the host syntax, as defined by Robert M. Hinden,		IPv6 literals in the host syntax, as defined by Robert M. Hinden,
	Brian E. Carpenter, and Larry Masinter in [RFC2732]. In addition,		Brian E. Carpenter, and Larry Masinter in [RFC2732]. In addition,
	contributions by Reese Anschultz, Tim Bray, Dan Connolly, Adam M.		contributions by Reese Anschultz, Tim Bray, Rob Cameron, Dan
	Costello, Jason Diamond, Martin Duerst, Henry Holtzman, Graham Klyne,		Connolly, Adam M. Costello, Jason Diamond, Martin Duerst, Stefan
	Dan Kohn, Bruce Lilly, Michael Mealling, Julian Reschke, Tomas		Eissing, Clive D.W. Feather, Pat Hayes, Henry Holtzman, Graham Klyne,
	Rokicki, Miles Sabin, Ronald Tschalaer, Marc Warne, Henry Zongaro,		Dan Kohn, Bruce Lilly, Andrew Main, Michael Mealling, Julian Reschke,
	and Zefram are gratefully acknowledged.		Tomas Rokicki, Miles Sabin, Ronald Tschalaer, Marc Warne, Stuart
			Williams, and Henry Zongaro are gratefully acknowledged.
	Normative References		Normative References
	[ASCII] American National Standards Institute, "Coded Character		[ASCII] American National Standards Institute, "Coded Character
	Set -- 7-bit American Standard Code for Information		Set -- 7-bit American Standard Code for Information
	Interchange", ANSI X3.4, 1986.		Interchange", ANSI X3.4, 1986.
	[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax		[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", RFC 2234, November 1997.		Specifications: ABNF", RFC 2234, November 1997.
	Non-normative References		Informative References
	[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and		[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
	Languages", BCP 18, RFC 2277, January 1998.		Languages", BCP 18, RFC 2277, January 1998.
	[RFC1630] Berners-Lee, T., "Universal Resource Identifiers in WWW: A		[RFC1630] Berners-Lee, T., "Universal Resource Identifiers in WWW: A
	Unifying Syntax for the Expression of Names and Addresses		Unifying Syntax for the Expression of Names and Addresses
	of Objects on the Network as used in the World-Wide Web",		of Objects on the Network as used in the World-Wide Web",
	RFC 1630, June 1994.		RFC 1630, June 1994.
	[RFC1738] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform		[RFC1738] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
	skipping to change at page 39, line 39 ¶		skipping to change at page 43, line 39 ¶
	Extensions (MIME) Part Two: Media Types", RFC 2046,		Extensions (MIME) Part Two: Media Types", RFC 2046,
	November 1996.		November 1996.
	[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.		[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.
	Jensen, "HTTP Extensions for Distributed Authoring --		Jensen, "HTTP Extensions for Distributed Authoring --
	WEBDAV", RFC 2518, February 1999.		WEBDAV", RFC 2518, February 1999.
	[RFC0952] Harrenstien, K., Stahl, M. and E. Feinler, "DoD Internet		[RFC0952] Harrenstien, K., Stahl, M. and E. Feinler, "DoD Internet
	host table specification", RFC 952, October 1985.		host table specification", RFC 952, October 1985.
	[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing		[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
	Architecture", RFC 2373, July 1998.		(IPv6) Addressing Architecture", RFC 3513, April 2003.
	[RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format for		[RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format for
	Literal IPv6 Addresses in URL's", RFC 2732, December 1999.		Literal IPv6 Addresses in URL's", RFC 2732, December 1999.
	[RFC1736] Kunze, J., "Functional Recommendations for Internet		[RFC1736] Kunze, J., "Functional Recommendations for Internet
	Resource Locators", RFC 1736, February 1995.		Resource Locators", RFC 1736, February 1995.
	[RFC1737] Masinter, L. and K. Sollins, "Functional Requirements for		[RFC1737] Masinter, L. and K. Sollins, "Functional Requirements for
	Uniform Resource Names", RFC 1737, December 1994.		Uniform Resource Names", RFC 1737, December 1994.
			[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
	[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",		[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
	STD 13, RFC 1034, November 1987.		STD 13, RFC 1034, November 1987.
	[RFC2110] Palme, J. and A. Hopmann, "MIME E-mail Encapsulation of		[RFC2110] Palme, J. and A. Hopmann, "MIME E-mail Encapsulation of
	Aggregate Documents, such as HTML (MHTML)", RFC 2110,		Aggregate Documents, such as HTML (MHTML)", RFC 2110,
	March 1997.		March 1997.
	[RFC2717] Petke, R. and I. King, "Registration Procedures for URL		[RFC2717] Petke, R. and I. King, "Registration Procedures for URL
	Scheme Names", BCP 35, RFC 2717, November 1999.		Scheme Names", BCP 35, RFC 2717, November 1999.
	skipping to change at page 41, line 4 ¶		skipping to change at page 45, line 29 ¶
	Roy T. Fielding		Roy T. Fielding
	Day Software		Day Software
	2 Corporate Plaza, Suite 150		2 Corporate Plaza, Suite 150
	Newport Beach, CA 92660		Newport Beach, CA 92660
	USA		USA
	Phone: +1-949-999-2523		Phone: +1-949-999-2523
	Fax: +1-949-644-5064		Fax: +1-949-644-5064
	EMail: roy.fielding@day.com		EMail: roy.fielding@day.com
	URI: http://www.apache.org/~fielding/		URI: http://www.apache.org/~fielding/
	Larry Masinter		Larry Masinter
	Adobe Systems Incorporated		Adobe Systems Incorporated
	345 Park Ave		345 Park Ave
	San Jose, CA 95110		San Jose, CA 95110
	USA		USA
	Phone: +1-408-536-3024		Phone: +1-408-536-3024
	EMail: LMM@acm.org		EMail: LMM@acm.org
	URI: http://larry.masinter.net/		URI: http://larry.masinter.net/
	Appendix A. Collected BNF for URI		Appendix A. Collected ABNF for URI
	To be filled-in later.		To be filled-in later.
	Appendix B. Parsing a URI Reference with a Regular Expression		Appendix B. Parsing a URI Reference with a Regular Expression
	As described in Section 4.3, the generic URI syntax is not sufficient		Since the "first-match-wins" algorithm is identical to the "greedy"
	to disambiguate the components of some forms of URI. Since the
	"greedy algorithm" described in that section is identical to the
	disambiguation method used by POSIX regular expressions, it is		disambiguation method used by POSIX regular expressions, it is
	natural and commonplace to use a regular expression for parsing the		natural and commonplace to use a regular expression for parsing the
	potential four components and fragment identifier of a URI reference.		potential five components of a URI reference.
	The following line is the regular expression for breaking-down a URI		The following line is the regular expression for breaking-down a
	reference into its components.		well-formed URI reference into its components.
	^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?		^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?
	12 3 4 5 6 7 8 9		12 3 4 5 6 7 8 9
	The numbers in the second line above are only to assist readability;		The numbers in the second line above are only to assist readability;
	they indicate the reference points for each subexpression (i.e., each		they indicate the reference points for each subexpression (i.e., each
	paired parenthesis). We refer to the value matched for subexpression		paired parenthesis). We refer to the value matched for subexpression
	<n> as $<n>. For example, matching the above expression to		<n> as $<n>. For example, matching the above expression to
	http://www.ics.uci.edu/pub/ietf/uri/#Related		http://www.ics.uci.edu/pub/ietf/uri/#Related
	skipping to change at page 43, line 50 ¶		skipping to change at page 47, line 48 ¶
	the case for the query component in the above example. Therefore, we		the case for the query component in the above example. Therefore, we
	can determine the value of the four components and fragment as		can determine the value of the four components and fragment as
	scheme = $2		scheme = $2
	authority = $4		authority = $4
	path = $5		path = $5
	query = $7		query = $7
	fragment = $9		fragment = $9
	and, going in the opposite direction, we can recreate a URI reference		and, going in the opposite direction, we can recreate a URI reference
	from its components using the algorithm of Section 5.2.		from its components using the algorithm of Section 5.3.
	Appendix C. Examples of Resolving Relative URI References
	Within an object with a well-defined base URI of
	http://a/b/c/d;p?q
	the relative URI would be resolved as follows:
	C.1 Normal Examples
	g:h = g:h
	g = http://a/b/c/g
	./g = http://a/b/c/g
	g/ = http://a/b/c/g/
	/g = http://a/g
	//g = http://g
	?y = http://a/b/c/d;p?y
	g?y = http://a/b/c/g?y
	#s = (current document)#s
	g#s = http://a/b/c/g#s
	g?y#s = http://a/b/c/g?y#s
	;x = http://a/b/c/;x
	g;x = http://a/b/c/g;x
	g;x?y#s = http://a/b/c/g;x?y#s
	. = http://a/b/c/
	./ = http://a/b/c/
	.. = http://a/b/
	../ = http://a/b/
	../g = http://a/b/g
	../.. = http://a/
	../../ = http://a/
	../../g = http://a/g
	C.2 Abnormal Examples
	Although the following abnormal examples are unlikely to occur in
	normal practice, all URI parsers should be capable of resolving them
	consistently. Each example uses the same base as above.
	An empty reference refers to the start of the current document.
	<> = (current document)
	Parsers must be careful in handling the case where there are more
	relative path ".." segments than there are hierarchical levels in the
	base URI's path. Note that the ".." syntax cannot be used to change
	the authority component of a URI.
	../../../g = http://a/../g
	../../../../g = http://a/../../g
	In practice, some implementations strip leading relative symbolic
	elements (".", "..") after applying a relative URI calculation, based
	on the theory that compensating for obvious author errors is better
	than allowing the request to fail. Thus, the above two references
	will be interpreted as "http://a/g" by some implementations.
	Similarly, parsers must avoid treating "." and ".." as special when
	they are not complete components of a relative path.
	/./g = http://a/./g
	/../g = http://a/../g
	g. = http://a/b/c/g.
	.g = http://a/b/c/.g
	g.. = http://a/b/c/g..
	..g = http://a/b/c/..g
	Less likely are cases where the relative URI uses unnecessary or
	nonsensical forms of the "." and ".." complete path segments.
	./../g = http://a/b/g
	./g/. = http://a/b/c/g/
	g/./h = http://a/b/c/g/h
	g/../h = http://a/b/c/h
	g;x=1/./y = http://a/b/c/g;x=1/y
	g;x=1/../y = http://a/b/c/y
	Some applications fail to separate the reference's query and/or
	fragment components from a relative path before merging it with the
	base path. This error is rarely noticed, since typical usage of a
	fragment never includes the hierarchy ("/") character, and the query
	component is not normally used within relative references.
	g?y/./x = http://a/b/c/g?y/./x
	g?y/../x = http://a/b/c/g?y/../x
	g#s/./x = http://a/b/c/g#s/./x
	g#s/../x = http://a/b/c/g#s/../x
	Some parsers allow the scheme name to be present in a relative URI if
	it is the same as the base URI scheme. This is considered to be a
	loophole in prior specifications of partial URI [RFC1630]. Its use
	should be avoided, but is allowed for backwards compatibility.
	http:g = http:g ; for validating parsers
	/ http://a/b/c/g ; for backwards compatibility
	Appendix D. Embedding the Base URI in HTML documents		Appendix C. Embedding the Base URI in HTML documents
	It is useful to consider an example of how the base URI of a document		It is useful to consider an example of how the base URI of a document
	can be embedded within the document's content. In this appendix, we		can be embedded within the document's content. In this appendix, we
	describe how documents written in the Hypertext Markup Language		describe how documents written in the Hypertext Markup Language
	(HTML) [HTML] can include an embedded base URI. This appendix does		(HTML) [HTML] can include an embedded base URI. This appendix does
	not form a part of the URI specification and should not be considered		not form a part of the URI specification and should not be considered
	as anything more than a descriptive example.		as anything more than a descriptive example.
	HTML defines a special element "BASE" which, when present in the		HTML defines a special element "BASE" which, when present in the
	"HEAD" portion of a document, signals that the parser should use the		"HEAD" portion of a document, signals that the parser should use the
	BASE element's "HREF" attribute as the base URI for resolving any		BASE element's "HREF" attribute as the base URI for resolving any
	relative URI. The "HREF" attribute must be an absolute URI. Note		relative URI. The "HREF" attribute must be an absolute URI. Note
	that, in HTML, element and attribute names are case-insensitive. For		that, in HTML, element and attribute names are case-insensitive. For
	example:		example:
	<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN">		<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN">
	<HTML><HEAD>		<HTML><HEAD>
	<TITLE>An example HTML document</TITLE>		<TITLE>An example HTML document</TITLE>
	<BASE href="http://www.example.com/Test/a/b/c">		<BASE href="http://www.example.com/Test/a/b/c">
	</HEAD><BODY>		</HEAD><BODY>
	... <A href="../x">a hypertext anchor</A> ...		... <A href="../x">a hypertext anchor</A> ...
	</BODY></HTML>		</BODY></HTML>
	A parser reading the example document should interpret the given		A parser reading the example document should interpret the given
	relative URI "../x" as representing the absolute URI		relative URI "../x" as representing the absolute URI
	<http://www.example.com/Test/a/x>		<http://www.example.com/Test/a/x>
	regardless of the context in which the example document was obtained.		regardless of the context in which the example document was obtained.
	Appendix E. Recommendations for Delimiting URI in Context		Appendix D. Delimiting a URI in Context
	URIs are often transmitted through formats that do not provide a		URIs are often transmitted through formats that do not provide a
	clear context for their interpretation. For example, there are many		clear context for their interpretation. For example, there are many
	occasions when a URI is included in plain text; examples include text		occasions when a URI is included in plain text; examples include text
	sent in electronic mail, USENET news messages, and, most importantly,		sent in electronic mail, USENET news messages, and, most importantly,
	printed on paper. In such cases, it is important to be able to		printed on paper. In such cases, it is important to be able to
	delimit the URI from the rest of the text, and in particular from		delimit the URI from the rest of the text, and in particular from
	punctuation marks that might be mistaken for part of the URI.		punctuation marks that might be mistaken for part of the URI.
	In practice, URI are delimited in a variety of ways, but usually		In practice, URI are delimited in a variety of ways, but usually
	skipping to change at page 47, line 27 ¶		skipping to change at page 49, line 27 ¶
	example.com/>, or just using whitespace		example.com/>, or just using whitespace
	http://example.com/		http://example.com/
	These wrappers do not form part of the URI.		These wrappers do not form part of the URI.
	In the case where a fragment identifier is associated with a URI		In the case where a fragment identifier is associated with a URI
	reference, the fragment would be placed within the brackets as well		reference, the fragment would be placed within the brackets as well
	(separated from the URI with a "#" character).		(separated from the URI with a "#" character).
	In some cases, extra whitespace (spaces, linebreaks, tabs, etc.) may		In some cases, extra whitespace (spaces, line-breaks, tabs, etc.) may
	need to be added to break a long URI across lines. The whitespace		need to be added to break a long URI across lines. The whitespace
	should be ignored when extracting the URI.		should be ignored when extracting the URI.
	No whitespace should be introduced after a hyphen ("-") character.		No whitespace should be introduced after a hyphen ("-") character.
	Because some typesetters and printers may (erroneously) introduce a		Because some typesetters and printers may (erroneously) introduce a
	hyphen at the end of line when breaking a line, the interpreter of a		hyphen at the end of line when breaking a line, the interpreter of a
	URI containing a line break immediately after a hyphen should ignore		URI containing a line break immediately after a hyphen should ignore
	all unescaped whitespace around the line break, and should be aware		all unescaped whitespace around the line break, and should be aware
	that the hyphen may or may not actually be part of the URI.		that the hyphen may or may not actually be part of the URI.
	skipping to change at page 48, line 9 ¶		skipping to change at page 50, line 4 ¶
	designators, though it is not commonly used in practice and is no		designators, though it is not commonly used in practice and is no
	longer recommended.		longer recommended.
	For robustness, software that accepts user-typed URI should attempt		For robustness, software that accepts user-typed URI should attempt
	to recognize and strip both delimiters and embedded whitespace.		to recognize and strip both delimiters and embedded whitespace.
	For example, the text:		For example, the text:
	Yes, Jim, I found it under "http://www.w3.org/Addressing/",		Yes, Jim, I found it under "http://www.w3.org/Addressing/",
	but you can probably pick it up from <ftp://ds.internic.		but you can probably pick it up from <ftp://ds.internic.
	net/rfc/>. Note the warning in <http://www.ics.uci.edu/pub/		net/rfc/>. Note the warning in <http://www.ics.uci.edu/pub/
	ietf/uri/historical.html#WARNING>.		ietf/uri/historical.html#WARNING>.
	contains the URI references		contains the URI references
	http://www.w3.org/Addressing/		http://www.w3.org/Addressing/
	ftp://ds.internic.net/rfc/		ftp://ds.internic.net/rfc/
	http://www.ics.uci.edu/pub/ietf/uri/historical.html#WARNING		http://www.ics.uci.edu/pub/ietf/uri/historical.html#WARNING
	Appendix F. Abbreviated URIs		Appendix E. Summary of Non-editorial Changes
	The URI syntax was designed for unambiguous reference to network
	resources and extensibility via the URI scheme. However, as URI
	identification and usage have become commonplace, traditional media
	(television, radio, newspapers, billboards, etc.) have increasingly
	used abbreviated URI references. That is, a reference consisting of
	only the authority and path portions of the identified resource, such
	as
	www.w3.org/Addressing/
	or simply the DNS hostname on its own. Such references are primarily
	intended for human interpretation rather than machine, with the
	assumption that context-based heuristics are sufficient to complete
	the URI (e.g., most hostnames beginning with "www" are likely to have
	a URI prefix of "http://"). Although there is no standard set of
	heuristics for disambiguating abbreviated URI references, many client
	implementations allow them to be entered by the user and
	heuristically resolved. It should be noted that such heuristics may
	change over time, particularly when new URI schemes are introduced.
	Since an abbreviated URI has the same syntax as a relative URI path,
	abbreviated URI references cannot be used in contexts where relative
	URIs are expected. This limits the use of abbreviated URIs to places
	where there is no defined base URI, such as dialog boxes and off-line
	advertisements.
	Appendix G. Summary of Non-editorial Changes
	G.1 Additions		E.1 Additions
	IPv6 literals have been added to the list of possible identifiers for		IPv6 literals have been added to the list of possible identifiers for
	the host portion of a server component, as described by [RFC2732],		the host portion of a authority component, as described by [RFC2732],
	with the addition of "[" and "]" to the reserved, uric, and		with the addition of "[" and "]" to the reserved and uric sets.
	uric-no-slash sets. Square brackets are now specified as reserved		Square brackets are now specified as reserved within the authority
	for the authority component, allowed within the opaque part of an		component and not allowed outside their use as delimiters for an
	opaque URI, and not allowed in the hierarchical syntax except for		IPv6reference within host. In order to make this change without
	their use as delimiters for an IPv6reference within host. In order		changing the technical definition of the path, query, and fragment
	to make this change without changing the technical definition of the		components, those rules were redefined to directly specify the
	path, query, and fragment components, those rules were redefined to		characters allowed rather than be defined in terms of uric.
	directly specify the characters allowed rather than continuing to be
	defined in terms of uric.
	Since [RFC2732] defers to [RFC2373] for definition of an IPv6 literal		Since [RFC2732] defers to [RFC3513] for definition of an IPv6 literal
	address, which unfortunately has an incorrect ABNF description of		address, which unfortunately lacks an ABNF description of
	IPv6address, we created a new ABNF rule for IPv6address that matches		IPv6address, we created a new ABNF rule for IPv6address that matches
	the text representations defined by Section 2.2 of [RFC2373].		the text representations defined by Section 2.2 of [RFC3513].
	Likewise, the definition of IPv4address has been improved in order to		Likewise, the definition of IPv4address has been improved in order to
	limit each decimal octet to the range 0-255, and the definition of		limit each decimal octet to the range 0-255, and the definition of
	hostname has been improved to better specify length limitations and		hostname has been improved to better specify length limitations and
	partially-qualified domain names.		partially-qualified domain names.
	Section 6 on URI normalization and comparison has been completely		Section 6 (Section 6) on URI normalization and comparison has been
	rewritten and extended using input from Tim Bray and discussion		completely rewritten and extended using input from Tim Bray and
	within the W3C Technical Architecture Group.		discussion within the W3C Technical Architecture Group. Likewise,
			Section 2.1 on the encoding of characters has been replaced.
	G.2 Modifications from RFC 2396		An ABNF production for URI has been introduced to correspond to the
			common usage of the term: an absolute URI with optional fragment.
			E.2 Modifications from RFC 2396
	The ad-hoc BNF syntax has been replaced with the ABNF of [RFC2234].		The ad-hoc BNF syntax has been replaced with the ABNF of [RFC2234].
	This change required all rule names that formerly included underscore		This change required all rule names that formerly included underscore
	characters to be renamed with a dash instead. Likewise, absoluteURI		characters to be renamed with a dash instead.
	and relativeURI have been changed to absolute-URI and relative-URI,
	respectively, for consistency.
	The ABNF of hier-part and relative-URI (Section 3) has been corrected		Section 2.2 on reserved characters has been rewritten to clearly
	to allow a relative URI path to be empty. This also allows an		explain what characters are reserved, when they are reserved, and why
	absolute-URI to consist of nothing after the "scheme:", as is present		they are reserved even when not used as delimiters by the generic
	in practice with the "DAV:" namespace [RFC2518] and the "about:" URI		syntax. Likewise, the section on escaped characters has been
	used by many browser implementations.		rewritten, and URI normalizers are now given license to unescape any
			octets corresponding to unreserved characters. The crosshatch ("#")
			character has been moved back from the excluded delims to the
			reserved set.
			The ABNF for URI and URI-reference has been redesigned to make them
			more friendly to LALR parsers and significantly reduce complexity. As
			a result, the layout form of syntax description has been removed,
			along with the uric-no-slash, opaque-part, and rel-segment
			productions. All references to "opaque" URIs have been replaced with
			a better description of how the path component may be opaque to
			hierarchy. The fragment identifier has been moved back into the
			section on generic syntax components and within the URI and
			relative-URI productions, though it remains excluded from
			absolute-URI. The ambiguity regarding the parsing of URI-reference as
			a URI or a relative-URI with a colon in the first segment is now
			explained and disambiguated in the section defining relative-URI.
			The ABNF of hier-part and relative-URI has been corrected to allow a
			relative URI path to be empty. This also allows an absolute-URI to
			consist of nothing after the "scheme:", as is present in practice
			with the "DAV:" namespace [RFC2518] and the "about:" URI used by many
			browser implementations. The ambiguity regarding the parsing of
			net-path, abs-path, and rel-path is now explained and disambiguated
			in the same section.
			Registry-based naming authorities that use the hierarchical authority
			syntax component are now limited to DNS hostnames, since those have
			been the only such URIs in deployment. This change was necessary to
			enable internationalized domain names to be processed in their native
			character encodings at the application layers above URI processing.
			The reg_name, server, and hostport productions have been removed to
			simplify parsing of the URI syntax.
	The ABNF of qualified has been simplified to remove a parsing		The ABNF of qualified has been simplified to remove a parsing
	ambiguity without changing the allowed syntax.		ambiguity without changing the allowed syntax. The toplabel
			production has been removed because it served no useful purpose. The
			ambiguity regarding the parsing of host as IPv4address or hostname is
			now explained and disambiguated in the same section.
	The resolving relative references algorithm of [RFC2396] has been		The resolving relative references algorithm of [RFC2396] has been
	rewritten using pseudocode for this revision to improve clarity and		rewritten using pseudocode for this revision to improve clarity and
	fix the following issues:		fix the following issues:
	o [RFC2396] section 5.2, step 6a, failed to account for a base URI		o [RFC2396] section 5.2, step 6a, failed to account for a base URI
	with no path.		with no path.
	o Restored the behavior of [RFC1808] where, if the the reference		o Restored the behavior of [RFC1808] where, if the reference
	contains an empty path and a defined query component, then the		contains an empty path and a defined query component, then the
	target URI inherits the base URI's path component.		target URI inherits the base URI's path component.
			o Removed the special-case treatment of same-document references in
			favor of a section that explains that a new retrieval action
			should not be made if the target URI and base URI, excluding
			fragments, match.
	Index		Index
	A		A
	abs-path 14		ABNF 9
	absolute-URI 14		abs-path 15
	absolute-URI-reference 20		absolute 9
			absolute-path 22
			absolute-URI 23
			access 7
	alphanum 17		alphanum 17
	authority 15		authority 15, 16
	D		D
	dec-octet 17		dec-octet 17
	delims 12		delims 13
			dereference 8
	domainlabel 17		domainlabel 17
			dot-segments 19
	E		E
	escaped 11		escaped 12
			excluded 13
	F		F
	fragment 20		fragment 20
			G
			generic syntax 5
	H		H
	h4 18		h4 18
	hier-part 14		hier-part 15
	host 16		hierarchical 9
			host 17
	hostname 17		hostname 17
	hostport 16
	I		I
			identifier 5
			invisible 13
	IPv4 17		IPv4 17
	IPv4address 17		IPv4address 17
	IPv6 18		IPv6 18
	IPv6address 18		IPv6address 18
	IPv6reference 18		IPv6reference 18
	L		L
			locator 6
	ls32 18		ls32 18
	M		M
	mark 11		mark 11
	N		N
	net-path 14		name 6
			net-path 15
	O		network-path 22
	opaque-part 14
	P		P
	path 18		path 15, 19
	path-segments 18		path-segments 19
	pchar 18		pchar 19
	port 16		port 18
	Q		Q
	qualified 17		qualified 17
	query 19		query 20
	R		R
	reg-name 16		rel-path 15
	rel-path 22		relative 9
	rel-segment 22		relative-path 22
	relative-URI 22		relative-URI 22
			representation 8
	reserved 10		reserved 10
			resolution 8
			resource 4
			retrieval 8
	S		S
			same-document 23
			sameness 8
	scheme 15		scheme 15
	segment 18		segment 19
	server 16		suffix 23
	T		T
	toplabel 17		transcription 6
	U		U
			uniform 4
	unreserved 11		unreserved 11
	unwise 12		unwise 13
	URI grammar		URI grammar
	abs-path 14		abs-path 15
	absolute-URI 14		absolute-URI 23
	absolute-URI-reference 20		ALPHA 9
	alphanum 17		alphanum 17
	authority 15		authority 15, 16
			CR 9
			CTL 9
	dec-octet 17		dec-octet 17
	delims 12		DIGIT 9
	domainlabel 17		domainlabel 17
	escaped 11		DQUOTE 9
	fragment 20		escaped 12
			fragment 15, 20, 22
	h4 18		h4 18
	hier-part 14		HEXDIG 9
	host 17		hier-part 15, 22, 23
			host 16, 17
	hostname 17		hostname 17
	hostport 17
	IPv4address 17		IPv4address 17
	IPv6address 18		IPv6address 18
	IPv6reference 18		IPv6reference 18
			LF 9
	ls32 18		ls32 18
	mark 11		mark 11
	net-path 14		net-path 15
	opaque-part 14		OCTET 9
	path 18		path-segments 15, 19
	path-segments 18		pchar 19, 20, 20
	pchar 18		port 16, 18
	port 17
	qualified 17		qualified 17
	query 19		query 15, 20, 22, 23
	reg-name 16		rel-path 15
	rel-path 22		relative-URI 22, 22
	rel-segment 22		reserved 11
	relative-URI 22		scheme 15, 16, 23
	reserved 10		segment 19
	scheme 15		SP 9
	segment 18
	server 16
	toplabel 17
	unreserved 11		unreserved 11
	unwise 12		URI 15, 22
	URI-reference 20		URI-reference 22
	uric 9		uric 10
	uric-no-slash 14		userinfo 16, 16
	userinfo 16		URI 15
	URI-reference 20		URI-reference 22
	uric 9		uric 10
	uric-no-slash 14		URL 6
			URN 6
	userinfo 16		userinfo 16
	Intellectual Property Statement		Intellectual Property Statement
	The IETF takes no position regarding the validity or scope of any		The IETF takes no position regarding the validity or scope of any
	intellectual property or other rights that might be claimed to		intellectual property or other rights that might be claimed to
	pertain to the implementation or use of the technology described in		pertain to the implementation or use of the technology described in
	this document or the extent to which any license under such rights		this document or the extent to which any license under such rights
	might or might not be available; neither does it represent that it		might or might not be available; neither does it represent that it
	has made any effort to identify any such rights. Information on the		has made any effort to identify any such rights. Information on the
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