Network Working Group C. Lilley Internet-Draft W3C Obsoletes: 3023 (if approved) M. Murata Updates: 4288, 4289, 6839 (if approved)International University of Japan Intended status: Standards Track A. Melnikov Expires: November 29, 2013 Isode Ltd. H. S. Thompson University of Edinburgh May 28, 2013 XML Media Types draft-ietf-appsawg-xml-mediatypes-01 Abstract This specification standardizes three media types -- application/xml, application/xml-external-parsed-entity, and application/xml-dtd -- for use in exchanging network entities that are related to the Extensible Markup Language (XML) while defining text/xml and text/ xml-external-parsed-entity as aliases for the respective application/ types. This specification also standardizes a convention (using the suffix '+xml') for naming media types outside of these five types when those media types represent XML MIME entities. Major differences from [RFC3023] are alignment of charset handling for text/xml and text/xml-external-parsed-entity with application/ xml, the addition of XPointer and XML Base as fragment identifiers and base URIs, respectively, mention of the XPointer Registry, and updating of many references. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 29, 2013. Lilley, et al. Expires November 29, 2013 [Page 1]
Internet-Draft XML Media Types May 2013 Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 3. XML Media Types . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Application/xml Registration . . . . . . . . . . . . . . 7 3.2. Text/xml Registration . . . . . . . . . . . . . . . . . . 9 3.3. Application/xml-external-parsed-entity Registration . . . 9 3.4. Text/xml-external-parsed-entity Registration . . . . . . 10 3.5. Application/xml-dtd Registration . . . . . . . . . . . . 10 3.6. Charset considerations . . . . . . . . . . . . . . . . . 11 3.6.1. Background . . . . . . . . . . . . . . . . . . . . . 12 4. The Byte Order Mark (BOM) and Conversions to/from the UTF-16 Charset . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5. Fragment Identifiers . . . . . . . . . . . . . . . . . . . . 12 6. The Base URI . . . . . . . . . . . . . . . . . . . . . . . . 13 7. XML Versions . . . . . . . . . . . . . . . . . . . . . . . . 14 8. A Naming Convention for XML-Based Media Types . . . . . . . . 14 8.1. Referencing . . . . . . . . . . . . . . . . . . . . . . . 16 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1. application/xml or text/xml with Omitted Charset and 8-bit MIME entity . . . . . . . . . . . . . . . . . . . . 17 9.2. application/xml or text/xml with Omitted Charset and 16-bit MIME entity . . . . . . . . . . . . . . . . . . . 17 9.3. application/xml or text/xml with UTF-8 Charset . . . . . 17 9.4. application/xml with UTF-16 Charset . . . . . . . . . . . 18 9.5. text/xml with UTF-16 Charset . . . . . . . . . . . . . . 18 9.6. application/xml with UTF-16BE Charset . . . . . . . . . . 18 9.7. text/xml with UTF-16BE Charset . . . . . . . . . . . . . 19 9.8. application/xml or text/xml with ISO-2022-KR Charset . . 19 9.9. application/xml or text/xml with Omitted Charset, no Internal Encoding Declaration and UTF-8 Entity . . . . . 19 9.10. application/xml or text/xml with Omitted Charset and Lilley, et al. Expires November 29, 2013 [Page 2]
Internet-Draft XML Media Types May 2013 Internal Encoding Declaration . . . . . . . . . . . . . . 20 9.11. application/xml-external-parsed-entity or text/xml- external-parsed-entity with UTF-8 Charset . . . . . . . . 20 9.12. application/xml-external-parsed-entity with UTF-16 Charset . . . . . . . . . . . . . . . . . . . . . . . . . 20 9.13. application/xml-external-parsed-entity with UTF-16BE Charset . . . . . . . . . . . . . . . . . . . . . . . . . 21 9.14. application/xml-dtd . . . . . . . . . . . . . . . . . . . 21 9.15. application/mathml+xml . . . . . . . . . . . . . . . . . 21 9.16. application/xslt+xml . . . . . . . . . . . . . . . . . . 21 9.17. application/rdf+xml . . . . . . . . . . . . . . . . . . . 22 9.18. image/svg+xml . . . . . . . . . . . . . . . . . . . . . . 22 9.19. model/x3d+xml . . . . . . . . . . . . . . . . . . . . . . 22 9.20. INCONSISTENT EXAMPLE: text/xml with UTF-8 Charset . . . . 22 9.21. application/soap+xml . . . . . . . . . . . . . . . . . . 23 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 12.1. Normative References . . . . . . . . . . . . . . . . . . 25 12.2. Informative References . . . . . . . . . . . . . . . . . 27 Appendix A. Why Use the '+xml' Suffix for XML-Based MIME Types? 28 Appendix B. Changes from RFC 3023 . . . . . . . . . . . . . . . 28 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 1. Introduction The World Wide Web Consortium has issued the Extensible Markup Language (XML) 1.0 [XML] and Extensible Markup Language (XML) 1.1 [XML1.1] specifications. To enable the exchange of XML network entities, this specification standardizes three media types -- application/xml, application/xml-external-parsed-entity, and application/xml-dtd and two aliases -- text/xml and text/xml- external-parsed-entity, as well as a naming convention for identifying XML-based MIME media types (using +xml). XML has been used as a foundation for other media types, including types in every branch of the IETF media types tree. To facilitate the processing of such types, and in line with the recognition in [RFC6838] of structured syntax name suffixes, a suffix of '+xml' is described in Section 8. This will allow generic XML-based tools -- browsers, editors, search engines, and other processors -- to work with all XML-based media types. 2. Notational Conventions Lilley, et al. Expires November 29, 2013 [Page 3]
Internet-Draft XML Media Types May 2013 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this specification are to be interpreted as described in [RFC2119]. As defined in [RFC2781] (informative), the three charsets "utf-16", "utf-16le", and "utf-16be" are used to label UTF-16 text. In this specification, "the UTF-16 family" refers to those three charsets. By contrast, the phrases "utf-16" or UTF-16 in this specification refer specifically to the single charset "utf-16". As sometimes happens between two communities, both MIME and XML have defined the term entity, with different meanings. Section 2.4 of [RFC2045] says: "The term 'entity' refers specifically to the MIME-defined header fields and contents of either a message or one of the parts in the body of a multipart entity." Section 4 of [XML] says: "An XML document may consist of one or many storage units. These are called entities; they all have content and are all (except for the document entity and the external DTD subset) identified by entity name". In this specification, "XML MIME entity" is defined as the latter (an XML entity) encapsulated in the former (a MIME entity). Furthermore, XML provides for the naming and referencing of entities for purposes of inclusion and/or substitution. In this specification "XML-entity declaration/reference/..." is used to avoid confusion when referring to such cases. 3. XML Media Types This specification standardizes three media types related to XML MIME entities: application/xml (with text/xml as an alias), application/ xml-external-parsed-entity (with text/xml-external-parsed-entity as an alias), and application/xml-dtd. Registration information for these media types is described in the sections below. Within the XML specification, XML MIME entities can be classified into four types. In the XML terminology, they are called "document entities", "external DTD subsets", "external parsed entities", and "external parameter entities". Appropriate usage for these types is as follows: Lilley, et al. Expires November 29, 2013 [Page 4]
Internet-Draft XML Media Types May 2013 document entities The media types application/xml or text/xml MAY be used external DTD subsets The media type application/xml-dtd SHOULD be used. The media types application/xml and text/xml MUST NOT be used. external parsed entities application/xml-external-parsed-entity or text/xml-external-parsed-entity SHOULD be used. The media types application/xml and text/xml MUST NOT be used unless the parsed entities are also well-formed "document entities" and are referenced as such. external parameter entities The media type application/xml-dtd SHOULD be used. The media types application/xml and text/xml MUST NOT be used. Note that [RFC3023] (which this specification obsoletes) recommended the use of text/xml and text/xml-external-parsed- entity for document entities and external parsed entities, respectively, but described charset handling which differed from common implementation practice. These media types are still commonly used, and this specification aligns the charset handling with industry practice. Note that [RFC2376] (which is obsolete) allowed application/xml and text/xml to be used for any of the four types, although in practice it is likely to have been rare. Neither external DTD subsets nor external parameter entities parse as XML documents, and while some XML document entities may be used as external parsed entities and vice versa, there are many cases where the two are not interchangeable. XML also has unparsed entities, internal parsed entities, and internal parameter entities, but they are not XML MIME entities. Application/xml and application/xml-external-parsed-entity are recommended. Compared to [RFC2376] or [RFC3023], this specification alters the charset handling of text/xml and text/xml-external-parsed- entity, treating them no differently from the respective application/ types. The reasons are as follows: Lilley, et al. Expires November 29, 2013 [Page 5]
Internet-Draft XML Media Types May 2013 Conflicting specifications regarding the character encoding have caused confusion. On the one hand, [RFC2046] specifies "The default character set, which must be assumed in the absence of a charset parameter, is US-ASCII.", [RFC2616] Section 3.7.1, defines that "media subtypes of the 'text' type are defined to have a default charset value of 'ISO-8859-1'", and [RFC2376] as well as [RFC3023] specify the default charset is US-ASCII. On the other hand, implementors and users of XML parsers, following Appendix F of [XML], assume that the default is provided by the XML encoding declaration or BOM. Note that this conflict did not exist for application/xml or application/xml-external- parsed-entity (see "Optional parameters" of application/xml registration in Section 3.1). The current situation, reflected in this specification, has been simplified by [RFC6657] updating [RFC2046] to remove the US-ASCII default. Furthermore, in accordance with [RFC6657]'s other recommendations, [HTTPbis] changes [RFC2616] by removing the ISO-8859-1 default and not defining any default at all. The top-level media type "text" has some restrictions on MIME entities and they are described in [RFC2045] and [RFC2046]. In particular, for transports other than HTTP [RFC2616] or HTTPS (which uses a MIME-like mechanism). the UTF-16 family, UCS-4, and UTF-32 are not allowed However, section 4.3.3 of [XML] says: "Each external parsed entity in an XML document may use a different encoding for its characters. All XML processors MUST be able to read entities in both the UTF-8 and UTF-16 encodings." Thus, although all XML processors can read entities in at least UTF-16, if an XML document or external parsed entity is encoded in such character encoding schemes, it could not be labeled as text/ xml or text/xml-external-parsed-entity (except for HTTP). It is not possible to deprecate text/xml because it is widely used in practice, and implementations are largely interoperable, following the rules of Appendix F of [XML] and ignoring the requirements of [RFC3023]. XML provides a general framework for defining sequences of structured data. In some cases, it may be desirable to define new media types that use XML but define a specific application of XML, perhaps due to domain-specific display, editing, security considerations or runtime Lilley, et al. Expires November 29, 2013 [Page 6]
Internet-Draft XML Media Types May 2013 information. Furthermore, such media types may allow UTF-8 or UTF-16 only and prohibit other charsets. This specification does not prohibit such media types and in fact expects them to proliferate. However, developers of such media types are STRONGLY RECOMMENDED to use this specification as a basis for their registration. In particular, the charset parameter, if used, MUST agree with the in- band XML encoding of the XML entity, as described in Section 3.6, in order to enhance interoperability. An XML document labeled as application/xml or text/xml, or with a +xml media type, might contain namespace declarations, stylesheet- linking processing instructions (PIs), schema information, or other declarations that might be used to suggest how the document is to be processed. For example, a document might have the XHTML namespace and a reference to a CSS stylesheet. Such a document might be handled by applications that would use this information to dispatch the document for appropriate processing. 3.1. Application/xml Registration MIME media type name: application MIME subtype name: xml Mandatory parameters: none Optional parameters: charset See Section 3.6. Encoding considerations: This media type MAY be encoded as appropriate for the charset and the capabilities of the underlying MIME transport. For 7-bit transports, data in either UTF-8 or UTF-16 MUST be encoded in quoted-printable or base64. For 8-bit clean transport (e.g., 8BITMIME [RFC6152] ESMTP or NNTP [RFC3977]), UTF-8 is not encoded, but the UTF-16 family MUST be encoded in base64. For binary clean transports (e.g., HTTP [RFC2616]), no content-transfer-encoding is necessary. Security considerations: See Section 11. Lilley, et al. Expires November 29, 2013 [Page 7]
Internet-Draft XML Media Types May 2013 Interoperability considerations: XML has proven to be interoperable across WebDAV clients and servers, and for import and export from multiple XML authoring tools. For maximum interoperability, validating processors are recommended. Although non-validating processors may be more efficient, they are not required to handle all features of XML. For further information, see sub-section 2.9 "Standalone Document Declaration" and section 5 "Conformance" of [XML] . Published specification: Extensible Markup Language (XML) 1.0 (Fifth Edition) [XML]. Applications which use this media type: XML is device-, platform-, and vendor-neutral and is supported by a wide range of Web user agents, WebDAV [RFC4918] clients and servers, as well as XML authoring tools. Additional information: Magic number(s): None. Although no byte sequences can be counted on to always be present, XML MIME entities in ASCII-compatible charsets (including UTF-8) often begin with hexadecimal 3C 3F 78 6D 6C ("<?xml"), and those in UTF-16 often begin with hexadecimal FE FF 00 3C 00 3F 00 78 00 6D 00 6C or FF FE 3C 00 3F 00 78 00 6D 00 6C 00 (the Byte Order Mark (BOM) followed by "<?xml"). For more information, see Appendix F of [XML]. File extension(s): .xml Macintosh File Type Code(s): "TEXT" Person and email address for further information: MURATA Makoto (FAMILY Given) <eb2m-mrt@asahi-net.or.jp> Alexey Melnikov <alexey.melnikov@isode.com> Chris Lilley <chris@w3.org> Henry S. Thompson <ht@inf.ed.ac.uk> Intended usage: COMMON Author/Change controller: The XML specification is a work product of the World Wide Web Consortium's XML Working Group, and was edited by: Lilley, et al. Expires November 29, 2013 [Page 8]
Internet-Draft XML Media Types May 2013 Tim Bray <tbray@textuality.com> Jean Paoli <jeanpa@microsoft.com> C. M. Sperberg-McQueen <cmsmcq@uic.edu> Eve Maler <eve.maler@east.sun.com> Francois Yergeau <mailto:francois@yergeau.com> 3.2. Text/xml Registration text/xml is an alias for application/xml, as defined in Section 3.1 above. 3.3. Application/xml-external-parsed-entity Registration MIME media type name: application MIME subtype name: xml-external-parsed-entity Mandatory parameters: none Optional parameters: charset See Section 3.6. Encoding considerations: Same as application/xml as described in Section 3.1. Security considerations: See Section 11. Interoperability considerations: XML external parsed entities are as interoperable as XML documents, though they have a less tightly constrained structure and therefore need to be referenced by XML documents for proper handling by XML processors. Similarly, XML documents cannot be reliably used as external parsed entities because external parsed entities are prohibited from having standalone document declarations or DTDs. Identifying XML external parsed entities with their own content type should enhance interoperability of both XML documents and XML external parsed entities. Published specification: Same as application/xml as described in Section 3.1. Applications which use this media type: Same as application/xml as described in Section 3.1. Lilley, et al. Expires November 29, 2013 [Page 9]
Internet-Draft XML Media Types May 2013 Additional information: Magic number(s): Same as application/xml as described in Section 3.1. File extension(s): .xml or .ent Macintosh File Type Code(s): "TEXT" Person and email address for further information: Same as application/xml as described in Section 3.1. Intended usage: COMMON Author/Change controller: Same as application/xml as described in Section 3.1. 3.4. Text/xml-external-parsed-entity Registration text/xml-external-parsed-entity is an alias for application/xml- external-parsed-entity, as defined in Section 3.3 above. 3.5. Application/xml-dtd Registration MIME media type name: application MIME subtype name: xml-dtd Mandatory parameters: none Optional parameters: charset See Section 3.6. Encoding considerations: Same as Section 3.1. Security considerations: See Section 11. Interoperability considerations: XML DTDs have proven to be interoperable by DTD authoring tools and XML browsers, among others. Published specification: Same as application/xml as described in Section 3.1. Lilley, et al. Expires November 29, 2013 [Page 10]
Internet-Draft XML Media Types May 2013 Applications which use this media type: DTD authoring tools handle external DTD subsets as well as external parameter entities. XML browsers may also access external DTD subsets and external parameter entities. Additional information: Magic number(s): Same as application/xml as described in Section 3.1. File extension(s): .dtd or .mod Macintosh File Type Code(s): "TEXT" Person and email address for further information: Same as application/xml as described in Section 3.1. Intended usage: COMMON Author/Change controller: Same as application/xml as described in Section 3.1. 3.6. Charset considerations [HST: new section pulled from section 3.2] The charset parameter MUST only be used, when the charset is reliably known and agrees with the in-band XML encoding declaration. This information can be used by non-XML processors to determine authoritatively the charset of the XML MIME entity. The charset parameter can also be used to provide protocol-specific operations, such as charset-based content negotiation in HTTP. "utf-8" [RFC3629] and "utf-16" [RFC2781] are the recommended values, representing the UTF-8 and UTF-16 charsets, respectively. These charsets are preferred since they are supported by all conforming processors of [XML]. If an entity of one of the types defined above is received where the charset parameter is omitted, no information is being provided about the charset by the MIME Content-Type header. Conforming XML processors MUST follow the requirements in section 4.3.3 of [XML] that directly address this contingency. However, MIME processors that are not XML processors SHOULD NOT assume a default charset if the charset parameter is omitted from such an entity. Lilley, et al. Expires November 29, 2013 [Page 11]
Internet-Draft XML Media Types May 2013 Since a receiving application can, with very high reliability, determine the encoding of an XML document by reading it, the in-band XML encoding declaration SHOULD be provided. 3.6.1. Background There are several reasons that the charset parameter is optionally allowed. First, recent web servers have been improved so that users can specify the charset parameter. Second, [RFC2130] (informative) specifies that the recommended specification scheme is the "charset" parameter. On the other hand, it has been argued that the charset parameter should be omitted and the mechanism described in Appendix F of [XML] (which is non-normative) should be solely relied on. This approach would allow users to avoid configuration of the charset parameter; an XML document stored in a file is likely to contain a correct encoding declaration or BOM (if necessary), since the operating system does not typically provide charset information for files. If users would like to rely on the in-band XML encoding declaration or BOM and/or to conceal charset information from non-XML processors, they can omit the parameter. 4. The Byte Order Mark (BOM) and Conversions to/from the UTF-16 Charset Section 4.3.3 of [XML] specifies that XML MIME entities in the charset "utf-16" MUST begin with a byte order mark (BOM), which is a hexadecimal octet sequence 0xFE 0xFF (or 0xFF 0xFE, depending on endian). The XML Recommendation further states that the BOM is an encoding signature, and is not part of either the markup or the character data of the XML document. Due to the presence of the BOM, applications that convert XML from "utf-16" to a non-Unicode encoding MUST strip the BOM before conversion. Similarly, when converting from another encoding into "utf-16", the BOM MUST be added after conversion is complete. In addition to the charset "utf-16", [RFC2781] introduces "utf-16le" (little endian) and "utf-16be" (big endian) as well. The BOM is prohibited for these charsets. When an XML MIME 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. Conversion from "utf-16" to "utf-16be" or "utf-16le" and conversion in the other direction MUST strip or add the BOM, respectively. 5. Fragment Identifiers Lilley, et al. Expires November 29, 2013 [Page 12]
Internet-Draft XML Media Types May 2013 Uniform Resource Identifiers (URIs) may contain fragment identifiers (see Section 3.5 of [RFC3986]). Likewise, Internationalized Resource Identifiers (IRIs) [RFC3987] may contain fragment identifiers. The syntax and semantics of fragment identifiers for the XML media types defined in this specification are based on the [XPointerFramework] W3C Recommendation. It allows simple names, and more complex constructions based on named schemes. When the syntax of a fragment identifier part of any URI or IRI with a retrieved media type governed by this specification conforms to the syntax specified in [XPointerFramework], conformant applications MUST interpret such fragment identifiers as designating that part of the retrieved representation specified by [XPointerFramework] and whatever other specifications define any XPointer schemes used. Conformant applications MUST support the 'element' scheme as defined in [XPointerElement], but need not support other schemes. If an XPointer error is reported in the attempt to process the part, this specification does not define an interpretation for the part. A registry of XPointer schemes [XPtrReg] is maintained at the W3C. Document authors SHOULD NOT use unregistered schemes. Scheme authors SHOULD register their schemes. See Section 8.1 for additional rquirements which apply when an XML- based MIME media type follows the naming convention '+xml'. If [XPointerFramework] and [XPointerElement] are inappropriate for some XML-based media type, it SHOULD NOT follow the naming convention '+xml'. When a URI has a fragment identifier, it is encoded by a limited subset of the repertoire of US-ASCII [ASCII] characters, as defined in [RFC3986]. When an IRI contains a fragment identifier, it is encoded by a much wider repertoire of characters. The conversion between IRI fragment identifiers and URI fragment identifiers is presented in Section 7 of [RFC3987]. 6. The Base URI Section 5.1 of [RFC3986] specifies that the semantics of a relative URI reference embedded in a MIME entity is dependent on the base URI. The base URI is either (1) the base URI embedded in context, (2) the base URI from the encapsulating entity, (3) the base URI from the Retrieval URI, or (4) the default base URI, where (1) has the highest precedence. [RFC3986] further specifies that the mechanism for embedding the base URI is dependent on the media type. Lilley, et al. Expires November 29, 2013 [Page 13]
Internet-Draft XML Media Types May 2013 The media type dependent mechanism for embedding the base URI in a MIME entity of type application/xml, text/xml, application/xml- external-parsed-entity or text/xml-external-parsed-entity is to use the xml:base attribute described in detail in [XBase]. Note that the base URI may be embedded in a different MIME entity, since the default value for the xml:base attribute may be specified in an external DTD subset or external parameter entity. 7. XML Versions application/xml, application/xml-external-parsed-entity, and application/xml-dtd, text/xml and text/xml-external-parsed-entity are to be used with [XML] In all examples herein where version="1.0" is shown, it is understood that version="1.1" may also be used, providing the content does indeed conform to [XML1.1]. The normative requirement of this specification upon XML is to follow the requirements of [XML], section 4.3.3. Except for minor clarifications, that section is substantially identical from the first edition to the current (5th) edition of XML 1.0, and for XML 1.1. Therefore, this specification may be used with any version or edition of XML 1.0 or 1.1. Specifications and recommendations based on or referring to this RFC SHOULD indicate any limitations on the particular versions of XML to be used. For example, a particular specification might indicate: "content MUST be represented using media-type application/xml, and the document must either (a) carry an xml declaration specifying version="1.0" or (b) omit the XML declaration, in which case per the XML recommendation the version defaults to 1.0" 8. A Naming Convention for XML-Based Media Types This specification recommends the use of a naming convention (a suffix of '+xml') for identifying XML-based MIME media types, whatever their particular content may represent, in line with the recognition in [RFC6838] of structured syntax name suffixes. This allows the use of generic XML processors and technologies on a wide variety of different XML document types at a minimum cost, using existing frameworks for media type registration. When a new media type is introduced for an XML-based format, the name of the media type SHOULD end with '+xml'. This convention will allow applications that can process XML generically to detect that the MIME entity is supposed to be an XML document, verify this assumption by invoking some XML processor, and then process the XML document accordingly. Applications may match for types that represent XML Lilley, et al. Expires November 29, 2013 [Page 14]
Internet-Draft XML Media Types May 2013 MIME entities by comparing the subtype to the pattern '*/*+xml'. (Of course, 4 of the 5 media types defined in this specification -- text/ xml, application/xml, text/xml-external-parsed-entity, and application/xml-external-parsed-entity -- also represent XML MIME entities while not conforming to the '*/*+xml' pattern.) NOTE: Section 14.1 of HTTP [RFC2616] does not support Accept headers of the form "Accept: */*+xml" and so this header MUST NOT be used in this way. Instead, content negotiation [RFC2703] could potentially be used if an XML-based MIME type were needed. Media types following the naming convention '+xml' SHOULD introduce the charset parameter for consistency, since XML-generic processing applies the same program for any such media type. However, there are some cases that the charset parameter need not be introduced. For example: When an XML-based media type is restricted to UTF-8, it is not necessary to introduce the charset parameter. "UTF-8 only" is a generic principle and UTF-8 is the default of XML. 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 UTF-8 nor UTF-16 require in-band XML encoding declarations. XML generic processing is not always appropriate for XML-based media types. For example, authors of some such media types may wish that the types remain entirely opaque except to applications that are specifically designed to deal with that media type. By NOT following the naming convention '+xml', such media types can avoid XML-generic processing. Since generic processing will be useful in many cases, however -- including in some situations that are difficult to predict ahead of time -- those registering media types SHOULD use the '+xml' convention unless they have a particularly compelling reason not to. The registration process for these media types is described in [RFC6838] and [RFC6839]. The registrar for the IETF tree will encourage new XML-based media type registrations in the IETF tree to follow this guideline. Registrars for other trees SHOULD follow this convention in order to ensure maximum interoperability of their XML- based documents. Similarly, media subtypes that do not represent XML MIME entities MUST NOT be allowed to register with a '+xml' suffix. *HST: What do we do about the registration of +xml in RFC6839? I think we need to reproduce it with appropriate changes, as it currently references 3023, and can be simplified/clarified by including it here. . .* Lilley, et al. Expires November 29, 2013 [Page 15]
Internet-Draft XML Media Types May 2013 8.1. Referencing Registrations for new XML-based media types under top-level types SHOULD, in specifying the charset parameter and encoding considerations, define them as: "Same as [charset parameter / encoding considerations] of application/xml as specified in RFC XXXX." The use of the charset parameter is STRONGLY RECOMMENDED, since this information can be used by XML processors to determine authoritatively the charset of the XML MIME entity. If there are some reasons not to follow this advice, they SHOULD be included as part of the registration. As shown above, two such reasons are "UTF-8 only" or "UTF-8 or UTF-16 only". These registrations SHOULD specify that the XML-based media type being registered has all of the security considerations described in RFC XXXX plus any additional considerations specific to that media type. These registrations SHOULD also make reference to RFC XXXX in specifying magic numbers, base URIs, and use of the BOM. When these registrations use the '+xml' convention, they MUST also make reference to RFC XXXX in specifying fragment identifier syntax and semantics, and they MAY restrict the syntax to a specified subset of schemes, except that they MUST NOT disallow barenames or 'element' scheme pointers. They MAY further require support for other registered schemes. They also MAY add additional syntax (which MUST NOT overlap with [XPointerFramework] syntax) together with associated semantics, and MAY add additional semantics for barename XPointers which, as provided for in Section 5, will only apply when this specification does not define an interpretation. These registrations MAY reference the application/xml registration in RFC XXXX in specifying interoperability considerations, if these considerations are not overridden by issues specific to that media type. 9. Examples The examples below give the value of the MIME Content-type header and the XML declaration (which includes the encoding declaration) inside the XML MIME entity. For UTF-16 examples, the Byte Order Mark character is denoted as "{BOM}", and the XML declaration is assumed to come at the beginning of the XML MIME entity, immediately following the BOM. Note that other MIME headers may be present, and the XML MIME entity may contain other data in addition to the XML Lilley, et al. Expires November 29, 2013 [Page 16]
Internet-Draft XML Media Types May 2013 declaration; the examples focus on the Content-type header and the encoding declaration for clarity. This section is non-normative. In particular, note that all "MUST" language herein reproduces or summarizes the consequences of normative statement already made above, and have no independent normative force. 9.1. application/xml or text/xml with Omitted Charset and 8-bit MIME entity Content-type: application/xml or text/xml <?xml version="1.0" encoding="iso-8859-1"?> Since the charset parameter is not provided in the Content-Type header, XML processors MUST treat the "iso-8859-1" encoding as authoritative. XML-unaware MIME processors SHOULD make no assumptions about the charset of the XML MIME entity. 9.2. application/xml or text/xml with Omitted Charset and 16-bit MIME entity Content-type: application/xml or text/xml {BOM}<?xml version="1.0" encoding="utf-16"?> or {BOM}<?xml version="1.0"?> This example shows a 16-bit MIME entity with no charset parameter. Since the charset parameter is not provided in the Content-Type header, in this case XML processors MUST treat the "utf-16" encoding and/or the BOM as authoritative. XML-unaware MIME processors SHOULD make no assumptions about the charset of the XML MIME entity. Omitting the charset parameter is NOT RECOMMENDED for application/xml when used with transports other than HTTP or HTTPS---text/xml SHOULD NOT be used for 16-bit MIME with transports other than HTTP or HTTPS (see. Section 9.5). 9.3. application/xml or text/xml with UTF-8 Charset Content-type: application/xml or text/xml; charset="utf-8" <?xml version="1.0" encoding="utf-8"?> Lilley, et al. Expires November 29, 2013 [Page 17]
Internet-Draft XML Media Types May 2013 This is the recommended encoding for use with all the media types defined in this specification. Since the charset parameter is provided, both MIME and XML processors MUST treat the enclosed entity as UTF-8 encoded. If sent using a 7-bit transport (e.g. SMTP [RFC5321]), the XML MIME entity MUST use a content-transfer-encoding of either quoted- printable or base64. For an 8-bit clean transport (e.g., 8BITMIME ESMTP or NNTP), or a binary clean transport (e.g., HTTP), no content- transfer-encoding is necessary. 9.4. application/xml with UTF-16 Charset Content-type: application/xml; charset="utf-16" {BOM}<?xml version="1.0" encoding="utf-16"?> or {BOM}<?xml version="1.0"?> If sent using a 7-bit transport (e.g., SMTP) or an 8-bit clean transport (e.g., 8BITMIME ESMTP or NNTP), the XML MIME entity MUST be encoded in quoted-printable or base64. For a binary clean transport (e.g., HTTP), no content-transfer-encoding is necessary. 9.5. text/xml with UTF-16 Charset Content-type: text/xml; charset="utf-16" {BOM}<?xml version='1.0' encoding='utf-16'?> or {BOM}<?xml version='1.0'?> This is possible only when the XML MIME entity is transmitted via HTTP or HTTPS, which use a MIME-like mechanism and are binary-clean protocols, hence do not perform CR and LF transformations and allow NUL octets. As described in [RFC2781], the UTF-16 family MUST NOT be used with media types under the top-level type "text" except over HTTP or HTTPS (see section 19.4.1 of [RFC2616] for details). Since HTTP is binary clean, no content-transfer-encoding is necessary. 9.6. application/xml with UTF-16BE Charset Lilley, et al. Expires November 29, 2013 [Page 18]
Internet-Draft XML Media Types May 2013 Content-type: application/xml; charset="utf-16be" <?xml version='1.0' encoding='utf-16be'?> Observe that the BOM does not exist. Since the charset parameter is provided, MIME and XML processors MUST treat the enclosed entity as UTF-16BE encoded. 9.7. text/xml with UTF-16BE Charset Content-type: text/xml; charset="utf-16be" <?xml version='1.0' encoding='utf-16be'?> Observe that the BOM does not exist. As for UTF-16, this is possible only when the XML MIME entity is transmitted via HTTP. 9.8. application/xml or text/xml with ISO-2022-KR Charset Content-type: application/xml; charset="iso-2022-kr" <?xml version="1.0" encoding="iso-2022-kr"?> This example shows the use of a Korean charset (e.g., Hangul) encoded following the specification in [RFC1557]. Since the charset parameter is provided, MIME processors MUST treat the enclosed entity as encoded per RFC 1557. Since the XML MIME entity has an internal encoding declaration (this example does show such a declaration, which agrees with the charset parameter) XML processors MUST also treat the enclosed entity as encoded per RFC 1557. Thus, interoperability is assured. Since ISO-2022-KR has been defined to use only 7 bits of data, no content-transfer-encoding is necessary with any transport. 9.9. application/xml or text/xml with Omitted Charset, no Internal Encoding Declaration and UTF-8 Entity Content-type: application/xml or text/xml <?xml version='1.0'?> In this example, the charset parameter has been omitted, the is no internal encoding declaration, and there is no BOM. Since there is no BOM, the XML processor follows the requirements in section 4.3.3, and optionally applies the mechanism described in Appendix F (which is non-normative) of [XML] to determine the charset encoding of UTF-8. Although the XML MIME entity does not contain an encoding Lilley, et al. Expires November 29, 2013 [Page 19]
Internet-Draft XML Media Types May 2013 declaration, the encoding actually _is_ UTF-8, so this is still a conforming XML MIME entity. An XML-unaware MIME processor SHOULD make no assumptions about the charset of the XML MIME entity. 9.10. application/xml or text/xml with Omitted Charset and Internal Encoding Declaration Content-type: application/xml or text/xml <?xml version='1.0' encoding="iso-10646-ucs-4"?> In this example, the charset parameter has been omitted, and there is no BOM. However, the XML MIME entity does have an encoding declaration inside the XML MIME entity that specifies the entity's charset. Following the requirements in section 4.3.3, and optionally applying the mechanism described in Appendix F (non-normative) of [XML], the XML processor determines the charset encoding of the XML MIME entity (in this example, UCS-4). An XML-unaware MIME processor SHOULD make no assumptions about the charset of the XML MIME entity. 9.11. application/xml-external-parsed-entity or text/xml-external- parsed-entity with UTF-8 Charset Content-type: text/xml-external-parsed-entity or application/xml- external-parsed-entity; charset="utf-8" <?xml encoding="utf-8"?> Since the charset parameter is provided, MIME and XML processors MUST treat the enclosed entity as UTF-8 encoded. If sent using a 7-bit transport (e.g. SMTP), the XML MIME entity MUST use a content-transfer-encoding of either quoted-printable or base64. For an 8-bit clean transport (e.g., 8BITMIME ESMTP or NNTP), or a binary clean transport (e.g., HTTP) no content-transfer-encoding is necessary. 9.12. application/xml-external-parsed-entity with UTF-16 Charset Content-type: application/xml-external-parsed-entity; charset="utf-16" {BOM}<?xml encoding="utf-16"?> Lilley, et al. Expires November 29, 2013 [Page 20]
Internet-Draft XML Media Types May 2013 or {BOM}<?xml?> Since the charset parameter is provided, MIME and XML processors MUST treat the enclosed entity as UTF-16 encoded. If sent using a 7-bit transport (e.g., SMTP) or an 8-bit clean transport (e.g., 8BITMIME ESMTP or NNTP), the XML MIME entity MUST be encoded in quoted-printable or base64. For a binary clean transport (e.g., HTTP), no content-transfer-encoding is necessary. 9.13. application/xml-external-parsed-entity with UTF-16BE Charset Content-type: application/xml-external-parsed-entity; charset="utf- 16be" <?xml encoding="utf-16be"?> Since the charset parameter is provided, MIME and XML processors MUST treat the enclosed entity as UTF-16BE encoded. 9.14. application/xml-dtd Content-type: application/xml-dtd; charset="utf-8" <?xml encoding="utf-8"?> Charset "utf-8" is a recommended charset value for use with application/xml-dtd. Since the charset parameter is provided, MIME and XML processors MUST treat the enclosed entity as UTF-8 encoded. 9.15. application/mathml+xml Content-type: application/mathml+xml <?xml version="1.0" ?> MathML documents are XML documents whose content describes mathematical information, as defined by [MathML]. As a format based on XML, MathML documents SHOULD follow the '+xml' suffix convention and use 'mathml+xml' in their MIME content-type identifier.This media type has been registered at IANA and is fully defined in [MathML]. 9.16. application/xslt+xml Content-type: application/xslt+xml Lilley, et al. Expires November 29, 2013 [Page 21]
Internet-Draft XML Media Types May 2013 <?xml version="1.0" ?> Extensible Stylesheet Language (XSLT) documents are XML documents whose content describes stylesheets for other XML documents, as defined by [XSLT]. As a format based on XML, XSLT documents SHOULD follow the '+xml' suffix convention and use 'xslt+xml' in their MIME content-type identifier.This media type has been registered at IANA and is fully defined in [XSLT]. 9.17. application/rdf+xml Content-type: application/rdf+xml <?xml version="1.0" ?> Resources identified using the application/rdf+xml media type are XML documents whose content describe RDF metadata. This media type has been registered at IANA and is fully defined in [RFC3870]. 9.18. image/svg+xml Content-type: image/svg+xml <?xml version="1.0" ?> Scalable Vector Graphics (SVG) documents are XML documents whose content describes graphical information, as defined by [SVG]. As a format based on XML, SVG documents SHOULD follow the '+xml' suffix convention and use 'svg+xml' in their MIME content-type identifier.The image/svg+xml media type has been registered at IANA and is fully defined in [SVG]. . 9.19. model/x3d+xml Content-type: model/x3d+xml <?xml version="1.0" ?> X3D is derived from VRML and is used for 3D models. Besides the XML representation, it may also be serialised in classic VRML syntax and using a fast infoset. Separate, but clearly related media types are used for these serialisations (model/x3d+vrml and model/ x3d+fastinfoset respectively). 9.20. INCONSISTENT EXAMPLE: text/xml with UTF-8 Charset Content-type: text/xml; charset="utf-8" Lilley, et al. Expires November 29, 2013 [Page 22]
Internet-Draft XML Media Types May 2013 <?xml version="1.0" encoding="iso-8859-1"?> Since the charset parameter is provided in the Content-Type header and differs from the XML encoding declaration , MIME and XML processors will not interoperate. MIME processors will treat the enclosed entity as UTF-8 encoded. That is, the "iso-8859-1" encoding will be be ignored. XML processors on the other hand will ignore the charset parameter and treat the XML entity as encoded in iso-8859-1. Processors generating XML MIME entities MUST NOT label conflicting charset information between the MIME Content-Type and the XML declaration. In particular, the addition of an explicit, site-wide charset without inspecting the XML MIME entity has frequently lead to interoperability problems. 9.21. application/soap+xml Content-type: application/soap+xml <?xml version="1.0" ?> Resources identified using the application/soap+xml media type are SOAP 1.2 message envelopes that have been serialized with XML 1.0. This media type has been registered at IANA and is fully defined in [RFC3902]. 10. IANA Considerations As described in Section 8, this specification updates the [RFC6838] and [RFC6839] registration process for XML-based MIME types. 11. Security Considerations XML MIME entities contain information which may be parsed and further processed by the recipient's XML system. These entities may contain and such systems may permit explicit system level commands to be executed while processing the data. To the extent that an XML system will execute arbitrary command strings, recipients of XML MIME entities may be a risk. In general, it may be possible to specify commands that perform unauthorized file operations or make changes to the display processor's environment that affect subsequent operations. In general, any information stored outside of the direct control of the user -- including CSS style sheets, XSL transformations, XML- entity declarations, and DTDs -- can be a source of insecurity, by either obvious or subtle means. For example, a tiny "whiteout attack" modification made to a "master" style sheet could make words Lilley, et al. Expires November 29, 2013 [Page 23]
Internet-Draft XML Media Types May 2013 in critical locations disappear in user documents, without directly modifying the user document or the stylesheet it references. Thus, the security of any XML document is vitally dependent on all of the documents recursively referenced by that document. The XML-entity lists and DTDs for XHTML 1.0 [XHTML], for instance, are likely to be a commonly used set of information. Many developers will use and trust them, few of whom will know much about the level of security on the W3C's servers, or on any similarly trusted repository. The simplest attack involves adding declarations that break validation. Adding extraneous declarations to a list of character XML-entities can effectively "break the contract" used by documents. A tiny change that produces a fatal error in a DTD could halt XML processing on a large scale. Extraneous declarations are fairly obvious, but more sophisticated tricks, like changing attributes from being optional to required, can be difficult to track down. Perhaps the most dangerous option available to crackers is redefining default values for attributes: e.g., if developers have relied on defaulted attributes for security, a relatively small change might expose enormous quantities of information. Apart from the structural possibilities, another option, "XML-entity spoofing," can be used to insert text into documents, vandalizing and perhaps conveying an unintended message. Because XML permits multiple XML-entity declarations, and the first declaration takes precedence, it's possible to insert malicious content where an XML- entity reference is used, such as by inserting the full text of Winnie the Pooh in every occurrence of —. Security considerations will vary by domain of use. For example, XML medical records will have much more stringent privacy and security considerations than XML library metadata. Similarly, use of XML as a parameter marshalling syntax necessitates a case by case security review. XML may also have some of the same security concerns as plain text. Like plain text, XML can contain escape sequences that, when displayed, have the potential to change the display processor environment in ways that adversely affect subsequent operations. Possible effects include, but are not limited to, locking the keyboard, changing display parameters so subsequent displayed text is unreadable, or even changing display parameters to deliberately obscure or distort subsequent displayed material so that its meaning is lost or altered. Display processors SHOULD either filter such material from displayed text or else make sure to reset all important settings after a given display operation is complete. Lilley, et al. Expires November 29, 2013 [Page 24]
Internet-Draft XML Media Types May 2013 Some terminal devices have keys whose output, when pressed, can be changed by sending the display processor a character sequence. If this is possible the display of a text object containing such character sequences could reprogram keys to perform some illicit or dangerous action when the key is subsequently pressed by the user. In some cases not only can keys be programmed, they can be triggered remotely, making it possible for a text display operation to directly perform some unwanted action. As such, the ability to program keys SHOULD be blocked either by filtering or by disabling the ability to program keys entirely. Note that it is also possible to construct XML documents that make use of what XML terms "[XML-]entity references" to construct repeated expansions of text. Recursive expansions are prohibited by [XML] and XML processors are required to detect them. However, even non- recursive expansions may cause problems with the finite computing resources of computers, if they are performed many times. (XML- entity A consists of 100 copies of XML-entity B, which in turn consists of 100 copies of XML-entity C, and so on) 12. References 12.1. Normative References [ASCII] , "US-ASCII. Coded Character Set -- 7-Bit American Standard Code for Information Interchange", ANSI X3.4-1986, 1986. [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC2781] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646", RFC 2781, Februrary 2000. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 3629, November 2003. Lilley, et al. Expires November 29, 2013 [Page 25]
Internet-Draft XML Media Types May 2013 [RFC3977] Feather, B., "Network News Transfer Protocol", RFC 3977, October 2006. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax.", RFC 3986, January 2005. [RFC3987] DUeerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, July 2005. [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, October 2008. [RFC6152] Klensin, J., Freed, N., Rose, M., and D. Crocker, "SMTP Service Extension for 8-bit MIME Transport", RFC 6152, March 2011. [RFC6657] Melnikov, A. and J. Reschke, "Update to MIME regarding "charset" Parameter Handling in Textual Media Types", RFC 6657, July 2012, <http://www.rfc-editor.org/rfc/rfc6657.txt>. [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, January 2013. [RFC6839] Hansen, T. and A. Melnikov, "Additional Media Type Structured Syntax Suffixes", RFC 6839, January 2013. [XBase] Marsh, J. and R. Tobin, "XML Base", World Wide Web Consortium Recommendation xmlbase, January 2009, <http://www.w3.org/TR/xmlbase>. [XML1.1] Bray, T., Paoli, J., Sperberg-McQueen, C.M., Maler, E., Yergeau, F., and J. Cowan, "Extensible Markup Language (XML) 1.1", World Wide Web Consortium Recommendation REC- xml, September 2006, <http://www.w3.org/TR/xml11>. [XML] Bray, T., Paoli, J., Sperberg-McQueen, C.M., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC-xml, November 2008, <http://www.w3.org/TR/REC-xml>. [XPointerElement] Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer element() Scheme", World Wide Web Consortium Recommendation REC-XPointer-Element, March 2003, <http://www.w3.org/TR/xptr-element/>. Lilley, et al. Expires November 29, 2013 [Page 26]
Internet-Draft XML Media Types May 2013 [XPointerFramework] Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer Framework", World Wide Web Consortium Recommendation REC- XPointer-Framework, March 2003, <http://www.w3.org/TR/xptr-framework/>. [XPtrReg] Hazael-Massieux, D., "XPointer Registry", 2005, <http://www.w3.org/2005/04/xpointer-schemes/>. 12.2. Informative References [CSS] Bos, B., Lie, H.W., Lilley, C., and I. Jacobs, "Cascading Style Sheets, level 2 (CSS2) Specification", World Wide Web Consortium Recommendation REC-CSS2, May 1998, <http://www.w3.org/TR/REC-CSS2/>. [HTTPbis] Fielding, R., "Hypertext Transfer Protocol -- HTTP/1.2?", RFC ???, January 2013. [ISO8859] , "ISO-8859. International Standard -- Information Processing -- 8-bit Single-Byte Coded Graphic Character Sets -- Part 1: Latin alphabet No. 1, ISO-8859-1:1987", 1987. [MathML] Carlisle, D., Ion, P., and R. Miner, "Mathematical Markup Language (MathML) Version 3.0", World Wide Web Consortium Recommendation MathML, October 2010, <http://www.w3.org/TR/MathML/>. [RFC1557] Choi, U., Chon, K., and H. Park, "Korean Character Encoding for Internet Messages", RFC 1557, December 1993. [RFC2130] Weider, C., Cecilia Preston, C., Simonsen, K., Alvestrand, H., Atkinson, R., Crispin, M., and P. Svanberg, "The Report of the IAB Character Set Workshop held 29 February - 1 March, 1996", RFC 2130, April 1997. [RFC2376] Whitehead, E. and M. Murata, "XML Media Types", RFC 2376, July 1998. [RFC2703] Klyne, G., "Protocol-independent Content Negotiation Framework", RFC 2703, September 1999. [RFC3023] Murata, M., St.Laurent, S., and D. Kohn, "XML Media Types", January 2001. [RFC3870] 3870, A., "application/rdf+xml Media Type Registration", RFC 3870, September 2004. Lilley, et al. Expires November 29, 2013 [Page 27]
Internet-Draft XML Media Types May 2013 [RFC3902] Baker, M. and M. Nottingham, "The "application/soap+xml" media type", RFC 3902, September 2004. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", RFC 4288, December 2005. [RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", RFC 4289, December 2005. [RFC4918] Dusseault, L., "HTTP Extensions for Distributed Authoring -- WEBDAV", RFC 4918, June 2007. [SVG] Dahlstroem, E. and others. , "Scalable Vector Graphics (SVG) 1.1 Specification (Second edition)", World Wide Web Consortium Recommendation SVG, August 2011, <http://www.w3.org/TR/SVG/>. [TAGMIME] Bray, T., Ed., "Internet Media Type registration, consistency of use", April 2004, <http://www.w3.org/2001/tag/2004/0430-mime>. [XHTML] Pemberton, S. and et al, "XHTML 1.0: The Extensible HyperText Markup Language", World Wide Web Consortium Recommendation xhtml1, December 1999, <http://www.w3.org/TR/xhtml1>. [XSLT] Kay, M., "XSL Transformations (XSLT) Version 2.0", World Wide Web Consortium Recommendation xslt20, January 2007, <http://www.w3.org/TR/xslt20/>. Appendix A. Why Use the '+xml' Suffix for XML-Based MIME Types? [RFC3023] contains a detailed discussion of the (at the time) novel use of a suffix, a practice which has since become widespread. Interested parties are referred to [RFC3023], Appendix A. Appendix B. Changes from RFC 3023 There are numerous and significant differences between this specification and [RFC3023], which it obsoletes. This appendix summarizes the major differences only. First, XPointer ([XPointerFramework] and [XPointerElement] has been added as fragment identifier syntax for "application/xml", and the XPointer Registry ([XPtrReg]) mentioned. Second, [XBase] has been added as a mechanism for specifying base URIs. Third, the language regarding charsets was updated to correspond to the W3C TAG finding Lilley, et al. Expires November 29, 2013 [Page 28]
Internet-Draft XML Media Types May 2013 Internet Media Type registration, consistency of use [TAGMIME]. Fourth, many references are updated, and the existence and relevance of XML 1.1 acknowledged. Finally, a number of justifications and contextualizations which were appropriate when XML was new have been removed, including the whole of the original Appendix A. Appendix C. Acknowledgements This specification reflects the input of numerous participants to the ietf-xml-mime@imc.org mailing list, though any errors are the responsibility of the authors. Special thanks to: Mark Baker, James Clark, Dan Connolly, Martin Duerst, Ned Freed, Yaron Goland, Rick Jelliffe, Larry Masinter, David Megginson, Keith Moore, Chris Newman, Gavin Nicol, Marshall Rose, Jim Whitehead and participants of the XML activity and the TAG at the W3C. Jim Whitehead and Simon St.Laurent are editors of [RFC2376] and [RFC3023], respectively. Authors' Addresses Chris Lilley World Wide Web Consortium 2004, Route des Lucioles - B.P. 93 06902 Sophia Antipolis Cedex France Email: chris@w3.org URI: http://www.w3.org/People/chris/ MURATA Makoto (FAMILY Given) International University of Japan Email: eb2m-mrt@asahi-net.or.jp Alexey Melnikov Isode Ltd. Email: alexey.melnikov@isode.com URI: http://www.melnikov.ca/ Lilley, et al. Expires November 29, 2013 [Page 29]
Internet-Draft XML Media Types May 2013 Henry S. Thompson University of Edinburgh Email: ht@inf.ed.ac.uk URI: http://www.ltg.ed.ac.uk/~ht/ Lilley, et al. Expires November 29, 2013 [Page 30]
