draft-ietf-appsawg-xml-mediatypes-09.txt		draft-ietf-appsawg-xml-mediatypes-10.txt
	Network Working Group H. Thompson		Network Working Group H. Thompson
	Internet-Draft University of Edinburgh		Internet-Draft University of Edinburgh
	Obsoletes: 3023 (if approved) C. Lilley		Obsoletes: 3023 (if approved) C. Lilley
	Updates: 6839 (if approved) W3C		Updates: 6839 (if approved) W3C
	Intended status: Standards Track March 02, 2014		Intended status: Standards Track April 07, 2014
	Expires: September 3, 2014		Expires: October 9, 2014
	XML Media Types		XML Media Types
	draft-ietf-appsawg-xml-mediatypes-09		draft-ietf-appsawg-xml-mediatypes-10
	Abstract		Abstract
	This specification standardizes three media types -- application/xml,		This specification standardizes three media types -- application/xml,
	application/xml-external-parsed-entity, and application/xml-dtd --		application/xml-external-parsed-entity, and application/xml-dtd --
	for use in exchanging network entities that are related to the		for use in exchanging network entities that are related to the
	Extensible Markup Language (XML) while defining text/xml and text/		Extensible Markup Language (XML) while defining text/xml and text/
	xml-external-parsed-entity as aliases for the respective application/		xml-external-parsed-entity as aliases for the respective application/
	types. This specification also standardizes the '+xml' suffix for		types. This specification also standardizes the '+xml' suffix for
	naming media types outside of these five types when those media types		naming media types outside of these five types when those media types
	skipping to change at page 1, line 39		skipping to change at page 1, line 39
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on September 3, 2014.		This Internet-Draft will expire on October 9, 2014.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 34		skipping to change at page 2, line 34
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Notational Conventions . . . . . . . . . . . . . . . . . . . 4		2. Notational Conventions . . . . . . . . . . . . . . . . . . . 4
	2.1. Conformance Keywords . . . . . . . . . . . . . . . . . . 4		2.1. Conformance Keywords . . . . . . . . . . . . . . . . . . 4
	2.2. Characters, Encodings, Charsets . . . . . . . . . . . . . 4		2.2. Characters, Encodings, Charsets . . . . . . . . . . . . . 4
	2.3. MIME Entities, XML Entities . . . . . . . . . . . . . . . 4		2.3. MIME Entities, XML Entities . . . . . . . . . . . . . . . 4
	3. Encoding Considerations . . . . . . . . . . . . . . . . . . . 5		3. Encoding Considerations . . . . . . . . . . . . . . . . . . . 5
	3.1. XML MIME producers . . . . . . . . . . . . . . . . . . . 6		3.1. XML MIME producers . . . . . . . . . . . . . . . . . . . 6
	3.2. XML MIME consumers . . . . . . . . . . . . . . . . . . . 6		3.2. XML MIME consumers . . . . . . . . . . . . . . . . . . . 6
	3.3. The Byte Order Mark (BOM) and Encoding Conversions . . . 7		3.3. The Byte Order Mark (BOM) and Encoding Conversions . . . 7
	4. XML Media Types . . . . . . . . . . . . . . . . . . . . . . . 8		4. XML Media Types . . . . . . . . . . . . . . . . . . . . . . . 8
	4.1. XML MIME Entities . . . . . . . . . . . . . . . . . . . . 8		4.1. XML MIME Entities . . . . . . . . . . . . . . . . . . . . 9
	4.2. Using '+xml' when Registering XML-based Media Types . . . 10		4.2. Using '+xml' when Registering XML-based Media Types . . . 10
	4.3. Registration Guidelines for XML-based Media Types Not		4.3. Registration Guidelines for XML-based Media Types Not
	Using '+xml' . . . . . . . . . . . . . . . . . . . . . . 11		Using '+xml' . . . . . . . . . . . . . . . . . . . . . . 12
	5. Fragment Identifiers . . . . . . . . . . . . . . . . . . . . 12		5. Fragment Identifiers . . . . . . . . . . . . . . . . . . . . 12
	6. The Base URI . . . . . . . . . . . . . . . . . . . . . . . . 13		6. The Base URI . . . . . . . . . . . . . . . . . . . . . . . . 13
	7. XML Versions . . . . . . . . . . . . . . . . . . . . . . . . 13		7. XML Versions . . . . . . . . . . . . . . . . . . . . . . . . 13
	8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14		8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14
	8.1. UTF-8 Charset . . . . . . . . . . . . . . . . . . . . . . 14		8.1. UTF-8 Charset . . . . . . . . . . . . . . . . . . . . . . 14
	8.2. UTF-16 Charset . . . . . . . . . . . . . . . . . . . . . 15		8.2. UTF-16 Charset . . . . . . . . . . . . . . . . . . . . . 15
	8.3. Omitted Charset and 8-bit MIME Entity . . . . . . . . . . 15		8.3. Omitted Charset and 8-bit MIME Entity . . . . . . . . . . 15
	8.4. Omitted Charset and 16-bit MIME Entity . . . . . . . . . 15		8.4. Omitted Charset and 16-bit MIME Entity . . . . . . . . . 16
	8.5. Omitted Charset, no Internal Encoding Declaration . . . . 16		8.5. Omitted Charset, no Internal Encoding Declaration . . . . 16
	8.6. UTF-16BE Charset . . . . . . . . . . . . . . . . . . . . 16		8.6. UTF-16BE Charset . . . . . . . . . . . . . . . . . . . . 17
	8.7. Non-UTF Charset . . . . . . . . . . . . . . . . . . . . . 17		8.7. Non-UTF Charset . . . . . . . . . . . . . . . . . . . . . 17
	8.8. INCONSISTENT EXAMPLE: Conflicting Charset and Internal		8.8. INCONSISTENT EXAMPLE: Conflicting Charset and Internal
	Encoding Declaration . . . . . . . . . . . . . . . . . . 17		Encoding Declaration . . . . . . . . . . . . . . . . . . 17
	8.9. INCONSISTENT EXAMPLE: Conflicting Charset and BOM . . . . 17		8.9. INCONSISTENT EXAMPLE: Conflicting Charset and BOM . . . . 18
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
	9.1. Application/xml Registration . . . . . . . . . . . . . . 18		9.1. Application/xml Registration . . . . . . . . . . . . . . 18
	9.2. Text/xml Registration . . . . . . . . . . . . . . . . . . 19		9.2. Text/xml Registration . . . . . . . . . . . . . . . . . . 20
	9.3. Application/xml-external-parsed-entity Registration . . . 20		9.3. Application/xml-external-parsed-entity Registration . . . 20
	9.4. Text/xml-external-parsed-entity Registration . . . . . . 21		9.4. Text/xml-external-parsed-entity Registration . . . . . . 21
	9.5. Application/xml-dtd Registration . . . . . . . . . . . . 21		9.5. Application/xml-dtd Registration . . . . . . . . . . . . 21
	9.6. The '+xml' Naming Convention for XML-Based Media Types . 22		9.6. The '+xml' Naming Convention for XML-Based Media Types . 22
	9.6.1. +xml Structured Syntax Suffix Registration . . . . . 22		9.6.1. +xml Structured Syntax Suffix Registration . . . . . 22
	10. Security Considerations . . . . . . . . . . . . . . . . . . . 23		10. Security Considerations . . . . . . . . . . . . . . . . . . . 24
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 25		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
	11.1. Normative References . . . . . . . . . . . . . . . . . . 25		11.1. Normative References . . . . . . . . . . . . . . . . . . 26
	11.2. Informative References . . . . . . . . . . . . . . . . . 27		11.2. Informative References . . . . . . . . . . . . . . . . . 28
	Appendix A. Why Use the '+xml' Suffix for XML-Based MIME Types? 30		Appendix A. Why Use the '+xml' Suffix for XML-Based MIME Types? 30
	Appendix B. Core XML specifications . . . . . . . . . . . . . . 30		Appendix B. Core XML specifications . . . . . . . . . . . . . . 30
	Appendix C. Changes from RFC 3023 . . . . . . . . . . . . . . . 30		Appendix C. Operational considerations . . . . . . . . . . . . . 31
	Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 31		C.1. General considerations . . . . . . . . . . . . . . . . . 31
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31		C.2. Considerations for producers . . . . . . . . . . . . . . 31
			C.3. Considerations for consumers . . . . . . . . . . . . . . 32
			Appendix D. Changes from RFC 3023 . . . . . . . . . . . . . . . 32
			Appendix E. Acknowledgements . . . . . . . . . . . . . . . . . . 33
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
	1. Introduction		1. Introduction
	The World Wide Web Consortium has issued the Extensible Markup		The World Wide Web Consortium has issued the Extensible Markup
	Language (XML) 1.0 [XML] and Extensible Markup Language (XML) 1.1		Language (XML) 1.0 [XML] and Extensible Markup Language (XML) 1.1
	[XML1.1] specifications. To enable the exchange of XML network		[XML1.1] specifications. To enable the exchange of XML network
	entities, this specification standardizes three media types --		entities, this specification standardizes three media types --
	application/xml, application/xml-external-parsed-entity, and		application/xml, application/xml-external-parsed-entity, and
	application/xml-dtd and two aliases -- text/xml and text/xml-		application/xml-dtd and two aliases -- text/xml and text/xml-
	external-parsed-entity, as well as a naming convention for		external-parsed-entity, as well as a naming convention for
	skipping to change at page 4, line 10		skipping to change at page 4, line 10
	with application/xml and application/xml-external-parsed-entity		with application/xml and application/xml-external-parsed-entity
	respectively, the addition of XPointer and XML Base as fragment		respectively, the addition of XPointer and XML Base as fragment
	identifiers and base URIs, respectively, integration of the XPointer		identifiers and base URIs, respectively, integration of the XPointer
	Registry and updating of many references.		Registry and updating of many references.
	2. Notational Conventions		2. Notational Conventions
	2.1. Conformance Keywords		2.1. Conformance Keywords
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	specification are to be interpreted as described in [RFC2119].		"OPTIONAL" in this specification are to be interpreted as described
			in [RFC2119].
	2.2. Characters, Encodings, Charsets		2.2. Characters, Encodings, Charsets
	Both XML (in an XML or Text declaration using the encoding pseudo-		Both XML (in an XML or Text declaration using the encoding pseudo-
	attribute) and MIME (in a Content-Type header field using the charset		attribute) and MIME (in a Content-Type header field using the charset
	parameter) use a common set of labels [IANA-charsets] to identify the		parameter) use a common set of labels [IANA-charsets] to identify the
	MIME charset (mapping from byte stream to character sequence		MIME charset (mapping from byte stream to character sequence
	[RFC2978]).		[RFC2978]).
	In this specification we will use the phrases "charset parameter" and		In this specification we will use the phrases "charset parameter" and
	skipping to change at page 4, line 34		skipping to change at page 4, line 35
	We reserve the phrase "character encoding" (or, when the context		We reserve the phrase "character encoding" (or, when the context
	makes the intention clear, simply "encoding") for the MIME charset		makes the intention clear, simply "encoding") for the MIME charset
	actually used in a particular XML MIME entity.		actually used in a particular XML MIME entity.
	[UNICODE] defines three "encoding forms", namely UTF-8, UTF-16, and		[UNICODE] defines three "encoding forms", namely UTF-8, UTF-16, and
	UTF-32. As UTF-8 can only be serialized in one way, the only		UTF-32. As UTF-8 can only be serialized in one way, the only
	possible label for UTF-8-encoded documents when serialised into MIME		possible label for UTF-8-encoded documents when serialised into MIME
	entities is "utf-8". UTF-16 XML documents, however, can be		entities is "utf-8". UTF-16 XML documents, however, can be
	serialised into MIME entities in one of two ways: either big- endian,		serialised into MIME entities in one of two ways: either big- endian,
	labelled (optionally) "utf-16" or "utf-16be", or little- endian,		labelled (optionally) "utf-16" or "utf-16be", or little- endian,
	labelled (optionally) "utf-16" or "utf-16le".		labelled (optionally) "utf-16" or "utf-16le". See Section 3.3 below
			for how a Byte Order Mark (BOM) is required when the "utf-16"
			serialization is used.
	UTF-32 has four potential serializations, of which only two (UTF-32BE		UTF-32 has four potential serializations, of which only two (UTF-32BE
	and UTF-32LE) are given names in in [UNICODE]. Support for the		and UTF-32LE) are given names in [UNICODE]. Support for the various
	various serializations varies widely, and security concerns about		serializations varies widely, and security concerns about their use
	their use have been raised. The use of UTF-32 is NOT RECOMMENDED for		have been raised (see for example [Sivonen]). The use of UTF-32 is
	XML MIME entities.		NOT RECOMMENDED for XML MIME entities.
	2.3. MIME Entities, XML Entities		2.3. MIME Entities, XML Entities
	As sometimes happens between two communities, both MIME and XML have		As sometimes happens between two communities, both MIME and XML have
	defined the term entity, with different meanings. Section 2.4 of		defined the term entity, with different meanings. Section 2.4 of
	[RFC2045] says:		[RFC2045] says:
	"The term 'entity' refers specifically to the MIME-defined header		"The term 'entity' refers specifically to the MIME-defined header
	fields and contents of either a message or one of the parts in the		fields and contents of either a message or one of the parts in the
	body of a multipart entity."		body of a multipart entity."
	skipping to change at page 6, line 11		skipping to change at page 6, line 17
	recommendations given below are intended to maximise interoperability		recommendations given below are intended to maximise interoperability
	in the face of this, by on the one hand mandating consistent		in the face of this, by on the one hand mandating consistent
	production and encouraging maximally robust forms of production, and		production and encouraging maximally robust forms of production, and
	on the other specifying recovery strategies to maximize the		on the other specifying recovery strategies to maximize the
	interoperability of consumers when the production rules are broken.		interoperability of consumers when the production rules are broken.
	3.1. XML MIME producers		3.1. XML MIME producers
	XML-aware MIME producers SHOULD supply a charset parameter and/or an		XML-aware MIME producers SHOULD supply a charset parameter and/or an
	appropriate BOM with non-UTF-8-encoded XML MIME entities which lack		appropriate BOM with non-UTF-8-encoded XML MIME entities which lack
	an encoding declaration, and SHOULD remove or correct an encoding		an encoding declaration. Such producers SHOULD remove or correct an
	declaration which is known to be incorrect (for example, as a result		encoding declaration which is known to be incorrect (for example, as
	of transcoding).		a result of transcoding).
	XML-aware MIME producers MUST supply an XML text declaration at the		XML-aware MIME producers MUST supply an XML text declaration at the
	beginning of non-UNICODE XML external parsed entities which would		beginning of non-UNICODE XML external parsed entities which would
	otherwise begin with the hexadecimal octet sequences 0xFE 0xFF, 0xFF		otherwise begin with the hexadecimal octet sequences 0xFE 0xFF, 0xFF
	0xFE or 0xEF 0xBB 0xBF, in order to avoid the mistaken detection of a		0xFE or 0xEF 0xBB 0xBF, in order to avoid the mistaken detection of a
	BOM.		BOM.
	XML-unaware MIME producers MUST NOT supply a charset parameter with		XML-unaware MIME producers MUST NOT supply a charset parameter with
	an XML MIME entity unless the entity's character encoding is reliably		an XML MIME entity unless the entity's character encoding is reliably
	known. Note that this is particularly relevant for central		known. Note that this is particularly relevant for central
	skipping to change at page 7, line 47		skipping to change at page 7, line 49
	If an XML MIME entity is received where the charset parameter is		If an XML MIME entity is received where the charset parameter is
	omitted, no information is being provided about the character		omitted, no information is being provided about the character
	encoding by the MIME Content-Type header. XML-aware consumers MUST		encoding by the MIME Content-Type header. XML-aware consumers MUST
	follow the requirements in section 4.3.3 of [XML] that directly		follow the requirements in section 4.3.3 of [XML] that directly
	address this case. XML-unaware MIME consumers SHOULD NOT assume a		address this case. XML-unaware MIME consumers SHOULD NOT assume a
	default encoding in this case.		default encoding in this case.
	3.3. The Byte Order Mark (BOM) and Encoding Conversions		3.3. The Byte Order Mark (BOM) and Encoding Conversions
	Section 4.3.3 of [XML] specifies that UTF-16 XML MIME entities not		Section 4.3.3 of [XML] specifies that UTF-16 XML MIME entities not
	labelled as "utf-16le" or "utf16-be" MUST begin with a byte order		labelled as "utf-16le" or "utf-16be" MUST begin with a byte order
	mark (BOM), U+FEFF, which appears as the hexadecimal octet sequence		mark (BOM), U+FEFF, which appears as the hexadecimal octet sequence
	0xFE 0xFF (big-endian) or 0xFF 0xFE (little-endian). [XML] further		0xFE 0xFF (big-endian) or 0xFF 0xFE (little-endian). [XML] further
	states that the BOM is an encoding signature, and is not part of		states that the BOM is an encoding signature, and is not part of
	either the markup or the character data of the XML document.		either the markup or the character data of the XML document.
	Due to the presence of the BOM, applications that convert XML from		Due to the presence of the BOM, applications that convert XML from
	UTF-16 to an encoding other than UTF-8 MUST strip the BOM before		UTF-16 to an encoding other than UTF-8 MUST strip the BOM before
	conversion. Similarly, when converting from another encoding into		conversion. Similarly, when converting from another encoding into
	UTF-16, either without a charset parameter, or labelled "utf-16", the		UTF-16, either without a charset parameter, or labelled "utf-16", the
	BOM MUST be added unless the original encoding was UTF-8 and a BOM		BOM MUST be added unless the original encoding was UTF-8 and a BOM
	skipping to change at page 8, line 24		skipping to change at page 8, line 26
	begin with a BOM, which appears as the hexadecimal octet sequence		begin with a BOM, which appears as the hexadecimal octet sequence
	0xEF 0xBB 0xBF. This is likewise defined to be an encoding		0xEF 0xBB 0xBF. This is likewise defined to be an encoding
	signature, and not part of either the markup or the character data of		signature, and not part of either the markup or the character data of
	the XML document.		the XML document.
	Applications that convert XML from UTF-8 to an encoding other than		Applications that convert XML from UTF-8 to an encoding other than
	UTF-16 MUST strip the BOM, if present, before conversion.		UTF-16 MUST strip the BOM, if present, before conversion.
	Applications which convert XML into UTF-8 MAY add a BOM.		Applications which convert XML into UTF-8 MAY add a BOM.
	In addition to the MIME charset "utf-16", [RFC2781] introduces "utf-		In addition to the MIME charset "utf-16", [RFC2781] introduces "utf-
	16le" (little endian) and "utf-16be" (big endian). The BOM is		16le" (little endian) and "utf-16be" (big endian). When an XML MIME
	prohibited in MIME entities with these labels. When an XML MIME
	entity is encoded in "utf-16le" or "utf-16be", it MUST NOT begin with		entity is encoded in "utf-16le" or "utf-16be", it MUST NOT begin with
	the BOM but SHOULD contain an in-band XML encoding declaration.		the BOM but SHOULD contain an in-band XML encoding declaration.
	Conversion from UTF-8 or UTF-16 (unlabelled, or labelled with		Conversion from UTF-8 or UTF-16 (unlabelled, or labelled with
	"utf-16") to "utf-16be" or "utf-16le" MUST strip a BOM if present,		"utf-16") to "utf-16be" or "utf-16le" MUST strip a BOM if present.
	and conversion in the other direction MUST (for UTF-16) or MAY (for		Conversion from UTF-16 labelled "utf-16le" or "utf-16be" to UTF-16
	UTF-8) add the appropriate BOM.		without a label or labelled "utf-16" MUST add the appropriate BOM.
			Conversion from UTF-16 labelled "utf-16le" or "utf-16be" to UTF-8 MAY
			add a UTF-8 BOM, but this is NOT RECOMMENDED.
	Appendix F of [XML] also implies the a UTF-32 BOM may be used in		Appendix F of [XML] also implies the a UTF-32 BOM may be used in
	conjunction with UTF-32-encoded documents. As noted above, this		conjunction with UTF-32-encoded documents. As noted above, this
	specification recommends against the use of UTF-32, but if it is		specification recommends against the use of UTF-32, but if it is
	used, the same considerations apply with respect to its being a		used, the same considerations apply with respect to its being a
	signature, not part of the document, with respect to transcoding into		signature, not part of the document, with respect to transcoding into
	or out of it and with respect to the MIME charsets "utf-32le" and		or out of it and with respect to the MIME charsets "utf-32le" and
	"utf-32be", as for UTF-16. Consumers which do not support UTF-32		"utf-32be", as for UTF-16. Consumers which do not support UTF-32
	SHOULD none-the-less recognise UTF-32 signatures in order to give		SHOULD none-the-less recognise UTF-32 signatures in order to give
	helpful error messages (instead of treating them as invalid UTF-16).		helpful error messages (instead of treating them as invalid UTF-16).
	skipping to change at page 11, line 4		skipping to change at page 11, line 12
	type. This convention will allow applications that can process XML		type. This convention will allow applications that can process XML
	generically to detect that the MIME entity is supposed to be an XML		generically to detect that the MIME entity is supposed to be an XML
	document, verify this assumption by invoking some XML processor, and		document, verify this assumption by invoking some XML processor, and
	then process the XML document accordingly. Applications may check		then process the XML document accordingly. Applications may check
	for types that represent XML MIME entities by comparing the last four		for types that represent XML MIME entities by comparing the last four
	characters of the subtype to the string '+xml'. (However note that 4		characters of the subtype to the string '+xml'. (However note that 4
	of the 5 media types defined in this specification -- text/xml,		of the 5 media types defined in this specification -- text/xml,
	application/xml, text/xml-external-parsed-entity, and application/		application/xml, text/xml-external-parsed-entity, and application/
	xml-external-parsed-entity -- also represent XML MIME entities while		xml-external-parsed-entity -- also represent XML MIME entities while
	not ending with '+xml'.)		not ending with '+xml'.)
	NOTE: Section 5.3.2 of HTTPbis [HTTPbis] does not support any form		NOTE: Section 5.3.2 of HTTPbis [HTTPbis] does not support any form
	of Accept header which will match only '+xml' types. In		of Accept header which will match only '+xml' types. In
	particular, Accept headers of the form "Accept: */*+xml" are not		particular, Accept headers of the form "Accept: */*+xml" are not
	allowed, and so this header MUST NOT be used for this purpose.		allowed, and will not work for this purpose.
	Media types following the naming convention '+xml' SHOULD introduce		Media types following the naming convention '+xml' SHOULD define the
	the charset parameter for consistency, since XML-generic processing		charset parameter for consistency, since XML-generic processing by
	applies the same program for any such media type. However, there are		definition treats treats all XML MIME entities uniformly as regards
	some cases that the charset parameter need not be introduced. For		character encoding information. However, there are some cases that
	example:		the charset parameter need not be defined. For example:
	When an XML-based media type is restricted to UTF-8, it is not		When an XML-based media type is restricted to UTF-8, it is not
	necessary to introduce the charset parameter. UTF-8 is the		necessary to define the charset parameter. UTF-8 is the default
	default for XML.		for XML.
	When an XML-based media type is restricted to UTF-8 and UTF-16, it		When an XML-based media type is restricted to UTF-8 and UTF-16, it
	might not be unreasonable to omit the charset parameter. Neither		might not be unreasonable to omit the charset parameter. Neither
	UTF-8 nor UTF-16 require XML encoding declarations.		UTF-8 nor UTF-16 require XML encoding declarations.
	XML generic processing is not always appropriate for XML-based media		XML generic processing is not always appropriate for XML-based media
	types. For example, authors of some such media types may wish that		types. For example, authors of some such media types may wish that
	the types remain entirely opaque except to applications that are		the types remain entirely opaque except to applications that are
	specifically designed to deal with that media type. By NOT following		specifically designed to deal with that media type. By NOT following
	the naming convention '+xml', such media types can avoid XML-generic		the naming convention '+xml', such media types can avoid XML-generic
	processing. Since generic processing will be useful in many cases,		processing. Since generic processing will be useful in many cases,
	however -- including in some situations that are difficult to predict		however -- including in some situations that are difficult to predict
	ahead of time -- the '+xml' convention is to be preferred unless		ahead of time -- the '+xml' convention is to be preferred unless
	there is some particularly compelling reason not to.		there is some particularly compelling reason not to.
	The registration process for specific '+xml' media types is described		The registration process for specific '+xml' media types is described
	in [RFC6838]. The registrar for the IETF tree will encourage new		in [RFC6838]. New XML-based media type registrations in the IETF
	XML-based media type registrations in the IETF tree to follow this		must follow these guidelines. When other organisations register XML-
	guideline. Registrars for other trees SHOULD follow this convention		based media types via the "Specification Required" IANA registration
	in order to ensure maximum interoperability of their XML-based		policy, the relevant Media Reviewer should ensure that they use the
	documents. Only media subtypes that represent XML MIME entities are		'+xml' convention, in order to ensure maximum interoperability of
	allowed to register with a '+xml' suffix.		their XML-based documents. Only media subtypes that represent XML
			MIME entities are allowed to register with a '+xml' suffix.
	In addition to the changes described above, the change controller has		In addition to the changes described above, the change controller has
	been changed to be the World Wide Web Consortium (W3C).		been changed to be the World Wide Web Consortium (W3C).
	4.3. Registration Guidelines for XML-based Media Types Not Using '+xml'		4.3. Registration Guidelines for XML-based Media Types Not Using '+xml'
	Registrations for new XML-based media types which do _not_ use the		Registrations for new XML-based media types which do _not_ use the
	'+xml' suffix SHOULD, in specifying the charset parameter and		'+xml' suffix SHOULD, in specifying the charset parameter and
	encoding considerations, define them as: "Same as [charset parameter		encoding considerations, define them as: "Same as [charset parameter
	/ encoding considerations] of application/xml as specified in RFC		/ encoding considerations] of application/xml as specified in RFC
	XXXX."		XXXX."
	Enabling the charset parameter is RECOMMENDED, since this information
			Defining the charset parameter is RECOMMENDED, since this information
	can be used by XML processors to determine authoritatively the		can be used by XML processors to determine authoritatively the
	character encoding of the XML MIME entity in the absence of a BOM.		character encoding of the XML MIME entity in the absence of a BOM.
	If there are some reasons not to follow this advice, they SHOULD be		If there are some reasons not to follow this advice, they SHOULD be
	included as part of the registration. As shown above, two such		included as part of the registration. As shown above, two such
	reasons are "UTF-8 only" or "UTF-8 or UTF-16 only".		reasons are "UTF-8 only" or "UTF-8 or UTF-16 only".
	These registrations SHOULD specify that the XML-based media type		These registrations SHOULD specify that the XML-based media type
	being registered has all of the security considerations described in		being registered has all of the security considerations described in
	RFC XXXX plus any additional considerations specific to that media		RFC XXXX plus any additional considerations specific to that media
	type.		type.
	skipping to change at page 12, line 49		skipping to change at page 13, line 12
	specified by the [XPointerFramework] together with any other		specified by the [XPointerFramework] together with any other
	specifications governing the XPointer schemes used in those		specifications governing the XPointer schemes used in those
	identifiers which the applications support. Conforming applications		identifiers which the applications support. Conforming applications
	MUST support the 'element' scheme as defined in [XPointerElement],		MUST support the 'element' scheme as defined in [XPointerElement],
	but need not support other schemes.		but need not support other schemes.
	If an XPointer error is reported in the attempt to process the part,		If an XPointer error is reported in the attempt to process the part,
	this specification does not define an interpretation for the part.		this specification does not define an interpretation for the part.
	A registry of XPointer schemes [XPtrReg] is maintained at the W3C.		A registry of XPointer schemes [XPtrReg] is maintained at the W3C.
	Document authors SHOULD NOT use unregistered schemes. Scheme authors		Generic processors of XML MIME entities SHOULD NOT implement
	SHOULD register their schemes ([XPtrRegPolicy] describes requirements		unregistered XPointer schemes ([XPtrRegPolicy] describes requirements
	and procedures for doing so).		and procedures for registering schemes).
	See Section 4.2 for additional requirements which apply when an XML-		See Section 4.2 for additional requirements which apply when an XML-
	based media type follows the naming convention '+xml'.		based media type follows the naming convention '+xml'.
	If [XPointerFramework] and [XPointerElement] are inappropriate for		If [XPointerFramework] and [XPointerElement] are inappropriate for
	some XML-based media type, it SHOULD NOT follow the naming convention		some XML-based media type, it SHOULD NOT follow the naming convention
	'+xml'.		'+xml'.
	When a URI has a fragment identifier, it is encoded by a limited		When a URI has a fragment identifier, it is encoded by a limited
	subset of the repertoire of US-ASCII characters, see		subset of the repertoire of US-ASCII characters, see
	skipping to change at page 29, line 5		skipping to change at page 29, line 25
	[RFC3977] Feather, B., "Network News Transfer Protocol", RFC 3977,		[RFC3977] Feather, B., "Network News Transfer Protocol", RFC 3977,
	October 2006.		October 2006.
	[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,		[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
	October 2008.		October 2008.
	[RFC6152] Klensin, J., Freed, N., Rose, M., and D. Crocker, "SMTP		[RFC6152] Klensin, J., Freed, N., Rose, M., and D. Crocker, "SMTP
	Service Extension for 8-bit MIME Transport", RFC 6152,		Service Extension for 8-bit MIME Transport", RFC 6152,
	March 2011.		March 2011.
			[Sivonen] Sivonen, H. and others, "Mozilla bug: Remove support for
			UTF-32 per HTML5 spec", October 2011, <https://
			bugzilla.mozilla.org/show_bug.cgi?id=604317#c6>.
	[TAGMIME] Bray, T., Ed., "Internet Media Type registration,		[TAGMIME] Bray, T., Ed., "Internet Media Type registration,
	consistency of use", April 2004,		consistency of use", April 2004,
	<http://www.w3.org/2001/tag/2004/0430-mime>.		<http://www.w3.org/2001/tag/2004/0430-mime>.
	[XHTML] Pemberton, S. and et al, "XHTML 1.0: The Extensible		[XHTML] Pemberton, S. and et al, "XHTML 1.0: The Extensible
	HyperText Markup Language", W3C Recommendation xhtml1,		HyperText Markup Language", W3C Recommendation xhtml1,
	December 1999,		December 1999,
	<http://www.w3.org/TR/2000/REC-xhtml1-20000126/>.		<http://www.w3.org/TR/2000/REC-xhtml1-20000126/>.
	Latest version available at [7].		Latest version available at [7].
	skipping to change at page 30, line 42		skipping to change at page 31, line 15
	The W3C Technical Architecture group has produced two documents which		The W3C Technical Architecture group has produced two documents which
	are also relevant:		are also relevant:
	The Self-Describing Web [FYN] discusses the overall principles of		The Self-Describing Web [FYN] discusses the overall principles of
	how document semantics are determined on the Web.		how document semantics are determined on the Web.
	Architecture of the World Wide Web, Volume One [AWWW], section		Architecture of the World Wide Web, Volume One [AWWW], section
	4.5.4, discusses the specific role of XML Namespace documents in		4.5.4, discusses the specific role of XML Namespace documents in
	this process.		this process.
	Appendix C. Changes from RFC 3023		Appendix C. Operational considerations
			This section provides an informal summary of the major operational
			considerations which arise when exchanging XML MIME entities over a
			network.
			C.1. General considerations
			The existence of both XML-aware and XML-unaware agents handling XML
			MIME entities can compromise introperability. Generic transcoding
			proxies pose a particular risk in this regard. Detailed advice about
			the handling of BOMs when transcoding can be found in Section 3.3.
			This specification requires XML consumers to treat BOMs as
			authoritative: this is in principle a backwards-incompatibility. In
			practice serious interoperability issues already exist when BOMs are
			used. Making BOMs authoritative, in conjunction with the deprecation
			of the UTF-32 encoding form and the requirement to include an XML
			encoding declaration in certain cases (Section 3.1), is intended to
			improve in-practice interoperability as much as possible over time.
			This specification establishes Section 5 as the basis for
			interpreting URIs for XML MIME entities which include fragment
			identifiers, mandates support only for shorthand ("simple name") and
			'element'-scheme fragments and deprecates support for unregistered
			XPointer schemes by XML MIME entity processors. Accordingly, URIs
			will interoperate best if they use only simple names and
			'element'-scheme fragment identifiers, with registered schemes
			varying widely in the degree of support to be found in generic tools.
			XPointer scheme authors can only expect generic tool support if they
			register their schemes.
			C.2. Considerations for producers
			Interoperability for all XML MIME entities is maximized by the use of
			UTF-8, without a BOM. When UTF-8 is _not_ used, a charset parameter
			and/or a BOM improve interoperability, particularly when XML-unaware
			consumers may be involved.
			In the very rare case where the substantive content of a non-UNICODE
			XML external parsed entity begins with the hexadecimal octet
			sequences 0xFE 0xFF, 0xFF 0xFE or 0xEF 0xBB 0xBF, including an XML
			text declaration will forestall the mistaken detection of a BOM.
			The use of UTF-32 for XML MIME entities puts interoperability at very
			high risk.
			Web-server configurations which supply default charset parameters
			risk misrepresenting XML MIME entities. Allowing users to control
			the value of charset parameters improves interoperability.
			Supplying a mistaken charset parameter is worse than supplying none
			at all. In particular, generic processors such as transcoders, when
			processing based on a mistaken charset parameter, if they do not fail
			altogether are likely to produce arbitrarily bogus results from which
			the original is not recoverable.
			C.3. Considerations for consumers
			Consumers of XML MIME entities can maximize interoperability by
			1. Taking a BOM as authoritative if it is present in an XML MIME
			entity;
			2. In the absence of a BOM, taking a charset parameter as
			authoritative if it is present.
			Assuming a default character encoding in the absence of a charset
			parameter harms interoperability.
			Although support for UTF-32 is not required by [XML] itself, and this
			specification deprecates its use, consumers which check for UTF-32
			BOMs can thereby avoid mistakenly processing UTF-32 entities as
			(invalid) UTF-16 entities.
			Appendix D. Changes from RFC 3023
	There are numerous and significant differences between this		There are numerous and significant differences between this
	specification and [RFC3023], which it obsoletes. This appendix		specification and [RFC3023], which it obsoletes. This appendix
	summarizes the major differences only.		summarizes the major differences only.
	XPointer ([XPointerFramework] and [XPointerElement]) has been		XPointer ([XPointerFramework] and [XPointerElement]) has been
	added as fragment identifier syntax for all the XML media types,		added as fragment identifier syntax for all the XML media types,
	and the XPointer Registry ([XPtrReg]) mentioned		and the XPointer Registry ([XPtrReg]) mentioned
	[XMLBase] has been added as a mechanism for specifying base URIs		[XMLBase] has been added as a mechanism for specifying base URIs
	skipping to change at page 31, line 17		skipping to change at page 33, line 17
	Priority is now given to a Byte Order Mark (BOM) if present		Priority is now given to a Byte Order Mark (BOM) if present
	Many references are updated, and the existence of XML 1.1 and		Many references are updated, and the existence of XML 1.1 and
	relevance of this specification to it acknowledged		relevance of this specification to it acknowledged
	A number of justifications and contextualizations which were		A number of justifications and contextualizations which were
	appropriate when XML was new have been removed, including the		appropriate when XML was new have been removed, including the
	whole of the original Appendix A		whole of the original Appendix A
	Making BOMs authoritative is in principle a backwards-		Appendix E. Acknowledgements
	incompatibility. In practice serious interoperability issues already
	exist when BOMs are used. Making BOMs authoritative, in conjunction
	with the deprecation of the UTF-32 encoding form and the requirement
	to include an XML encoding declaration in certain cases
	(Section 3.1), is intended to improve in-practice interoperability as
	much as possible.
	Appendix D. Acknowledgements
	MURATA Makoto (FAMILY Given) and Alexey Melnikov made early and		MURATA Makoto (FAMILY Given) and Alexey Melnikov made early and
	important contributions to the effort to revise [RFC3023].		important contributions to the effort to revise [RFC3023].
	This specification reflects the input of numerous participants to the		This specification reflects the input of numerous participants to the
	ietf-xml-mime@imc.org, xml-mime@ietf.org and apps-discuss@ietf.org		ietf-xml-mime@imc.org, xml-mime@ietf.org and apps-discuss@ietf.org
	mailing lists, though any errors are the responsibility of the		mailing lists, though any errors are the responsibility of the
	authors. Special thanks to:		authors. Special thanks to:
	Mark Baker, James Clark, Dan Connolly, Martin Duerst, Ned Freed,		Mark Baker, James Clark, Dan Connolly, Martin Duerst, Ned Freed,
	Yaron Goland, Bjoern Hoehrmann, Rick Jelliffe, Murray S. Kucherawy,		Yaron Goland, Bjoern Hoehrmann, Rick Jelliffe, Murray S. Kucherawy,
	Larry Masinter, David Megginson, S. Moonesamy, Keith Moore, Chris		Larry Masinter, David Megginson, S. Moonesamy, Keith Moore, Chris
	Newman, Gavin Nicol, Julian Reschke, Marshall Rose, Jim Whitehead,		Newman, Gavin Nicol, Julian Reschke, Marshall Rose, Jim Whitehead,
	Erik Wilde and participants of the XML activity and the TAG at the		Erik Wilde and participants of the XML activity and the TAG at the
	W3C.		W3C.
	Jim Whitehead and Simon St.Laurent were editors of [RFC2376] and		Jim Whitehead and Simon St. Laurent were editors of [RFC2376] and
	[RFC3023], respectively.		[RFC3023], respectively.
	Authors' Addresses		Authors' Addresses
	Henry S. Thompson		Henry S. Thompson
	University of Edinburgh		University of Edinburgh
	Email: ht@inf.ed.ac.uk		Email: ht@inf.ed.ac.uk
	URI: http://www.ltg.ed.ac.uk/~ht/		URI: http://www.ltg.ed.ac.uk/~ht/
	Chris Lilley		Chris Lilley
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