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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group N. Freed 3 Internet-Draft Oracle 4 Obsoletes: 4288 (if approved) J. Klensin 5 Expires: October 3, 2012 6 T. Hansen 7 AT&T Laboratories 8 April 1, 2012 10 Media Type Specifications and Registration Procedures 11 draft-ietf-appsawg-media-type-regs-04 13 Abstract 15 This document defines procedures for the specification and 16 registration of media types for use in HTTP, MIME and other Internet 17 protocols. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on October 3, 2012. 36 Copyright Notice 38 Copyright (c) 2012 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 1.1. Historical Note . . . . . . . . . . . . . . . . . . . . . 4 55 1.2. Conventions Used in This Document . . . . . . . . . . . . 4 56 2. Media Type Registration Preliminaries . . . . . . . . . . . . 5 57 3. Registration Trees and Subtype Names . . . . . . . . . . . . . 5 58 3.1. Standards Tree . . . . . . . . . . . . . . . . . . . . . . 5 59 3.2. Vendor Tree . . . . . . . . . . . . . . . . . . . . . . . 6 60 3.3. Personal or Vanity Tree . . . . . . . . . . . . . . . . . 7 61 3.4. Unregistered x. Tree . . . . . . . . . . . . . . . . . . . 7 62 3.5. Additional Registration Trees . . . . . . . . . . . . . . 8 63 4. Registration Requirements . . . . . . . . . . . . . . . . . . 8 64 4.1. Functionality Requirement . . . . . . . . . . . . . . . . 8 65 4.2. Naming Requirements . . . . . . . . . . . . . . . . . . . 8 66 4.2.1. Text Media Types . . . . . . . . . . . . . . . . . . . 9 67 4.2.2. Image Media Types . . . . . . . . . . . . . . . . . . 10 68 4.2.3. Audio Media Types . . . . . . . . . . . . . . . . . . 10 69 4.2.4. Video Media Types . . . . . . . . . . . . . . . . . . 11 70 4.2.5. Application Media Types . . . . . . . . . . . . . . . 11 71 4.2.6. Multipart and Message Media Types . . . . . . . . . . 11 72 4.2.7. Additional Top-level Types . . . . . . . . . . . . . . 12 73 4.2.8. Structured Syntax Name Suffixes . . . . . . . . . . . 12 74 4.2.9. Deprecated Aliases . . . . . . . . . . . . . . . . . . 13 75 4.3. Parameter Requirements . . . . . . . . . . . . . . . . . . 13 76 4.4. Canonicalization and Format Requirements . . . . . . . . . 14 77 4.5. Interchange Recommendations . . . . . . . . . . . . . . . 14 78 4.6. Security Requirements . . . . . . . . . . . . . . . . . . 15 79 4.7. Requirements specific to XML media types . . . . . . . . . 16 80 4.8. Encoding Requirements . . . . . . . . . . . . . . . . . . 16 81 4.9. Usage and Implementation Non-requirements . . . . . . . . 17 82 4.10. Publication Requirements . . . . . . . . . . . . . . . . . 17 83 4.11. Additional Information . . . . . . . . . . . . . . . . . . 18 84 5. Media Type Registration Procedures . . . . . . . . . . . . . . 19 85 5.1. Preliminary Community Review . . . . . . . . . . . . . . . 19 86 5.2. Submit request to IANA . . . . . . . . . . . . . . . . . . 19 87 5.2.1. Provisional Registrations . . . . . . . . . . . . . . 20 88 5.3. Review and Approval . . . . . . . . . . . . . . . . . . . 20 89 5.4. Comments on Media Type Registrations . . . . . . . . . . . 21 90 5.5. Location of Registered Media Type List . . . . . . . . . . 21 91 5.6. Change Procedures . . . . . . . . . . . . . . . . . . . . 21 92 5.7. Registration Template . . . . . . . . . . . . . . . . . . 22 93 6. Structured Syntax Suffix Registration Procedures . . . . . . . 23 94 6.1. Change Procedures . . . . . . . . . . . . . . . . . . . . 24 95 6.2. Structured Syntax Suffix Registration Template . . . . . . 24 97 7. Security Considerations . . . . . . . . . . . . . . . . . . . 25 98 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 99 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26 100 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 101 10.1. Normative References . . . . . . . . . . . . . . . . . . . 26 102 10.2. Informative References . . . . . . . . . . . . . . . . . . 27 103 Appendix A. Grandfathered Media Types . . . . . . . . . . . . . . 28 104 Appendix B. Changes Since RFC 4288 . . . . . . . . . . . . . . . 28 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 107 1. Introduction 109 Recent Internet protocols have been carefully designed to be easily 110 extensible in certain areas. In particular, many protocols, 111 including but not limited to HTTP [RFC2616] and MIME [RFC2045], are 112 capable of carrying arbitrary labeled content. A mechanism is needed 113 to label such content and a registration process is needed for these 114 labels, so that that the set of such values are defined in a 115 reasonably orderly, well-specified, and public manner. 117 This document defines media type specification and registration 118 procedures that use the Internet Assigned Numbers Authority (IANA) as 119 a central registry. 121 1.1. Historical Note 123 The media type registration process was initially defined for 124 registering media types for use in the context of the asynchronous 125 Internet mail environment. In this mail environment there is a need 126 to limit the number of possible media types, to increase the 127 likelihood of interoperability when the capabilities of the remote 128 mail system are not known. As media types are used in new 129 environments in which the proliferation of media types is not a 130 hindrance to interoperability, the original procedure proved 131 excessively restrictive and had to be generalized. This was 132 initially done in [RFC2048], but the procedure defined there was 133 still part of the MIME document set. The media type specification 134 and registration procedure has now been moved to this separate 135 document, to make it clear that it is independent of MIME. 137 It may be desirable to restrict the use of media types to specific 138 environments or to prohibit their use in other environments. This 139 revision incorporates such restrictions into media type registrations 140 in a systematic way. See Section 4.9 for additional discussion. 142 1.2. Conventions Used in This Document 144 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 145 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 146 document are to be interpreted as described in [RFC2119]. 148 This specification makes use of the Augmented Backus-Naur Form (ABNF) 149 [RFC5234] notation, including the core rules defined in Appendix A of 150 that document. 152 2. Media Type Registration Preliminaries 154 Registration of a new media type or types starts with the 155 construction of a registration proposal. Registration may occur 156 within several different registration trees that have different 157 requirements, as discussed below. In general, a new registration 158 proposal is circulated and reviewed in a fashion appropriate to the 159 tree involved. The media type is then registered if the proposal is 160 acceptable. The following sections describe the requirements and 161 procedures used for each of the different registration trees. 163 3. Registration Trees and Subtype Names 165 In order to increase the efficiency and flexibility of the 166 registration process, different structures of subtype names may be 167 registered to accommodate the different natural requirements for, 168 e.g., a subtype that will be recommended for wide support and 169 implementation by the Internet community, or a subtype that is used 170 to move files associated with proprietary software. The following 171 subsections define registration "trees" that are distinguished by the 172 use of faceted names, e.g., names of the form 173 "tree.subtree...subtype". Note that some media types defined prior 174 to this document do not conform to the naming conventions described 175 below. See Appendix A for a discussion of them. 177 3.1. Standards Tree 179 The standards tree is intended for types of general interest to the 180 Internet community. Registrations in the standards tree MUST be 181 either: 183 1. in the case of registrations in IETF specifications, approved 184 directly by the IESG, or 186 2. registered by a recognized standards body using the 187 "Specification Required" IANA registration policy [RFC5226] 188 (which implies Expert Review). 190 The first procedure is used for registering registrations from IETF 191 Consensus documents, or in rare cases when registering a 192 grandfathered (see Appendix A) and/or otherwise incomplete 193 registration is in the interest of the Internet community. 195 In the second case the IESG makes a one time decision on whether the 196 registration submitter represents a recognized standards body; after 197 that, a Media Types Reviewer (Designated Expert or a group of 198 Designated Experts) performs the Expert Review as specified in this 199 document. Subsequent submissions from the same source do not involve 200 the IESG. 202 In the case of registration for the IETF itself, the registration 203 proposal MUST be published as an IETF Consensus RFC, which can be on 204 the Standards Track, a BCP, Informational, or Experimental. In the 205 case of registrations for other recognized standards bodies, the 206 format MUST be described by a formal standards specification produced 207 by that body. 209 Registrations published in non-IETF RFC streams are allowed and 210 require IESG approval. 212 Standards-tree registration RFCs can either be standalone 213 "registration only" RFCs, or they can be incorporated into a more 214 general specification of some sort. 216 Media types in the standards tree are normally denoted by names that 217 are not explicitly faceted, i.e., do not contain period (".", full 218 stop) characters. 220 The "owner" of a media type registration in the standards tree is 221 assumed to be the standards body itself. Modification or alteration 222 of the specification uses the same level of processing (e.g., a 223 registration submitted on Standards Track can be revised in another 224 Standards Track RFC, but cannot be revised in an Informational RFC) 225 required for the initial registration. 227 Standards-tree registrations from recognized standards bodies may be 228 submitted directly to the IANA, where they will undergo Expert Review 229 [RFC5226] prior to approval. In this case, the Expert Reviewer(s) 230 will, among other things, ensure that the required specification 231 provides adequate documentation. 233 3.2. Vendor Tree 235 The vendor tree is used for media types associated with publicly 236 available products. "Vendor" and "producer" are construed very 237 broadly in this context and are considered equivalent. Note that 238 industry consortia as well as non-commercial entities that do not 239 qualify as recognized standards bodies can quite appropriately 240 register media types in the vendor tree. 242 A registration may be placed in the vendor tree by anyone who needs 243 to interchange files associated with some product or set of products. 244 However, the registration properly belongs to the vendor or 245 organization producing the software that employs the type being 246 registered, and that vendor or organization can at any time elect to 247 assert ownership of the registration. 249 When a third party registers a type on behalf of someone else both 250 entites SHOULD be noted in the Change Controller field in the 251 registration. One possible format for this would be "Foo, on behalf 252 of Bar". 254 Registrations in the vendor tree will be distinguished by the leading 255 facet "vnd.". That may be followed, at the discretion of the 256 registrant, by either a media subtype name from a well-known producer 257 (e.g., "vnd.mudpie") or by an IANA-approved designation of the 258 producer's name that is followed by a media type or product 259 designation (e.g., vnd.bigcompany.funnypictures). 261 While public exposure and review of media types to be registered in 262 the vendor tree is not required, using the ietf-types@iana.org 263 mailing list for review is encouraged to improve the quality of those 264 specifications. Registrations in the vendor tree may be submitted 265 directly to the IANA, where they will undergo Expert Review [RFC5226] 266 prior to approval. 268 3.3. Personal or Vanity Tree 270 Registrations for media types created experimentally or as part of 271 products that are not distributed commercially may be registered in 272 the personal or vanity tree. The registrations are distinguished by 273 the leading facet "prs.". 275 The owner of "personal" registrations and associated specifications 276 is the person or entity making the registration, or one to whom 277 responsibility has been transferred as described below. 279 While public exposure and review of media types to be registered in 280 the personal tree is not required, using the ietf-types@iana.org 281 mailing list (see Section 5.1) for review is encouraged to improve 282 the quality of those specifications. Registrations in the personal 283 tree may be submitted directly to the IANA, where they will undergo 284 Expert Review [RFC5226] prior to approval. 286 3.4. Unregistered x. Tree 288 Subtype names with "x." as the first facet may be used for types 289 intended exclusively for use in private, local environments. Types 290 in this tree cannot be registered and are intended for use only with 291 the active agreement of the parties exchanging them. 293 However, with the simplified registration procedures described above 294 for vendor and personal trees, it should rarely, if ever, be 295 necessary to use unregistered types. Therefore, use of types in the 296 "x." tree is strongly discouraged. 298 Note that types with names beginning with "x-" are no longer 299 considered to members of this tree (see [I-D.ietf-appsawg-xdash]). 300 Also note that if a generally useful and widely deployed type 301 incorrectly ends up with an "x-" name prefix, it MAY be registered 302 using its current name in an alternate tree by following the 303 procedure defined in Appendix A. 305 3.5. Additional Registration Trees 307 From time to time and as required by the community, new top-level 308 registration trees may be created by IETF Standards Action. It is 309 explicitly assumed that these trees may be created for external 310 registration and management by well-known permanent bodies; for 311 example, scientific societies may register media types specific to 312 the sciences they cover. In general, the quality of review of 313 specifications for one of these additional registration trees is 314 expected to be equivalent to registrations in the standards tree by a 315 recognized Standards Development Organization. When the IETF 316 performs such review, it needs to consider the greater expertise of 317 the requesting body with respect to the subject media type. 319 4. Registration Requirements 321 Media type registrations are all expected to conform to various 322 requirements laid out in the following sections. Note that 323 requirement specifics sometimes vary depending on the registration 324 tree, again as detailed in the following sections. 326 4.1. Functionality Requirement 328 Media types MUST function as an actual media format. Registration of 329 things that are better thought of as a transfer encoding, as a 330 charset, or as a collection of separate entities of another type, is 331 not allowed. For example, although applications exist to decode the 332 base64 transfer encoding [RFC2045], base64 cannot be registered as a 333 media type. 335 This requirement applies regardless of the registration tree 336 involved. 338 4.2. Naming Requirements 340 All registered media types MUST be assigned type and subtype names. 341 The combination of these names serves to uniquely identify the media 342 type, and the format of the subtype name identifies the registration 343 tree. Both type and subtype names are case-insensitive. 345 Type and subtype names MUST conform to the following ABNF: 347 type-name = restricted-name 348 subtype-name = restricted-name 350 restricted-name = 1*127restricted-name-chars 351 restricted-name-chars = ALPHA / DIGIT / "!" / 352 "#" / "$" / "&" / "." / 353 "+" / "-" / "^" / "_" 355 Note that this syntax is somewhat more restrictive than what is 356 allowed by the ABNF in section 5.1 of [RFC2045]. Also note that 357 while this syntax allows names of up to 127 characters, 358 implementation limits may make such long names problematic. For this 359 reason the components of names SHOULD be limited to 64 characters. 361 Although the name syntax treates "+" as equivalent to any other 362 character, it is used in media type names to introduce a structured 363 syntax specificer suffix. Structured syntax suffix requirements are 364 specified in Section 4.2.8. 366 While it is possible for a given media type to be assigned additional 367 names, the use of different names to identify the same media type is 368 discouraged. 370 These requirements apply regardless of the registration tree 371 involved. 373 The choice of top-level type name MUST take into account the nature 374 of media type involved. New subtypes of top-level types MUST conform 375 to the restrictions of the top-level type, if any. The following 376 sections describe each of the initial set of top-level types and 377 their associated restrictions. Additionally, various protocols, 378 including but not limited to HTTP and MIME, MAY impose additional 379 restrictions on the media types they can transport. (See [RFC2046] 380 for additional information on the restrictions MIME imposes.) 382 4.2.1. Text Media Types 384 The "text" media type is intended for sending material that is 385 principally textual in form. 387 Many subtypes of text, notably including the subtype "text/plain", 388 which is a generic subtype for plain text defined in [RFC2046], 389 define a "charset" parameter. If a "charset" parameter is defined 390 for a particular subtype of text, it MUST be used to specify a 391 charset name defined in accordance to the procedures laid out in 392 [RFC2978]. 394 A "charset" parameter SHOULD NOT be specified when charset 395 information is transported inside the payload (e.g., as in "text/ 396 xml"). 398 If a "charset" parameter is specified, it SHOULD be a required 399 parameter, eliminating the options of specifying a default value. If 400 there is a strong reason for the parameter to be optional despite 401 this advice, each subtype MAY specify its own default value, or 402 alternately, it MAY specify that there is no default value. Finally, 403 the "UTF-8" charset [RFC3629] SHOULD be selected as the default. See 404 [I-D.ietf-appsawg-mime-default-charset] for additional information on 405 the use of "charset" parameters in conjunction with subtypes of text. 407 Plain text does not provide for or allow formatting commands, font 408 attribute specifications, processing instructions, interpretation 409 directives, or content markup. Plain text is seen simply as a linear 410 sequence of characters, possibly interrupted by line breaks or page 411 breaks. Plain text MAY allow the stacking of several characters in 412 the same position in the text. Plain text in scripts like Arabic and 413 Hebrew may also include facilities that allow the arbitrary mixing of 414 text segments with different writing directions. 416 Beyond plain text, there are many formats for representing what might 417 be known as "rich text". An interesting characteristic of many such 418 representations is that they are to some extent readable even without 419 the software that interprets them. It is useful to distinguish them, 420 at the highest level, from such unreadable data as images, audio, or 421 text represented in an unreadable form. In the absence of 422 appropriate interpretation software, it is reasonable to present 423 subtypes of "text" to the user, while it is not reasonable to do so 424 with most non-textual data. Such formatted textual data should be 425 represented using subtypes of "text". 427 4.2.2. Image Media Types 429 A media type of "image" indicates that the content specifies one or 430 more individual images. The subtype names the specific image format. 432 4.2.3. Audio Media Types 434 A media type of "audio" indicates that the content contains audio 435 data. 437 4.2.4. Video Media Types 439 A media type of "video" indicates that the content specifies a time- 440 varying-picture image, possibly with color and coordinated sound. 441 The term 'video' is used in its most generic sense, rather than with 442 reference to any particular technology or format, and is not meant to 443 preclude subtypes such as animated drawings encoded compactly. 445 Note that although in general this document strongly discourages the 446 mixing of multiple media in a single body, it is recognized that many 447 so-called video formats include a representation for synchronized 448 audio and/or text, and this is explicitly permitted for subtypes of 449 "video". 451 4.2.5. Application Media Types 453 The "application" media type is to be used for discrete data that do 454 not fit in any of the media types, and particularly for data to be 455 processed by some type of application program. This is information 456 that must be processed by an application before it is viewable or 457 usable by a user. Expected uses for the "application" media type 458 include but are not limited to file transfer, spreadsheets, 459 presentations, scheduling data, and languages for "active" 460 (computational) material. (The last, in particular, can pose 461 security problems that must be understood by implementors, and that 462 are considered in detail in the discussion of the "application/ 463 postscript" media type in [RFC2046].) 465 For example, a meeting scheduler might define a standard 466 representation for information about proposed meeting dates. An 467 intelligent user agent would use this information to conduct a dialog 468 with the user, and might then send additional material based on that 469 dialog. More generally, there have been several "active" languages 470 developed in which programs in a suitably specialized language are 471 transported to a remote location and automatically run in the 472 recipient's environment. Such applications may be defined as 473 subtypes of the "application" media type. 475 The subtype of "application" will often either be the name or include 476 part of the name of the application for which the data are intended. 477 This does not mean, however, that any application program name may 478 simply be used freely as a subtype of "application"; the subtype 479 needs to be registered. 481 4.2.6. Multipart and Message Media Types 483 Multipart and message are composite types, that is, they provide a 484 means of encapsulating zero or more objects, each labeled with its 485 own media type. 487 All subtypes of multipart and message MUST conform to the syntax 488 rules and other requirements specified in [RFC2046] and amended by 489 Section 3.5 of [RFC6532]. 491 4.2.7. Additional Top-level Types 493 In some cases a new media type may not "fit" under any currently 494 defined top-level content type. Such cases are expected to be quite 495 rare. However, if such a case does arise a new top-level type can be 496 defined to accommodate it. Such a definition MUST be done via 497 standards-track RFC; no other mechanism can be used to define 498 additional top-level content types. 500 4.2.8. Structured Syntax Name Suffixes 502 [RFC3023] defined the first such augmentation to the media type 503 definition to additionally specify the underlying structure of that 504 media type. To quote: 506 This document also standardizes a convention (using the suffix 507 '+xml') for naming media types ... when those media types 508 represent XML MIME (Multipurpose Internet Mail Extensions) 509 entities. 511 That is, it specified a suffix (in that case, "+xml") to be appended 512 to the base media type name. 514 Since this was published, the defacto practice has arisen for using 515 this suffix convention for other well-known structuring syntaxes. In 516 particular, media types have been registered with suffixes such as 517 "+der", "+fastinfoset" and "+json". This specification formalizes 518 this practice and sets up a registry for structured type name 519 suffixes. 521 The primary guideline for whether a structured type name suffix 522 should be registerable is that it be described by a readily-available 523 description, preferably within a document published by an established 524 standards organization, and for which there's a reference that can be 525 used in a References section of an RFC. 527 Media types that make use of a named structured syntax SHOULD use the 528 appropriate registered "+suffix" for that structured syntax when they 529 are registered. By the same token, media types MUST NOT be given 530 names incorporating suffixes for structured syntaxes they do not 531 actually employ. "+suffix" constructs for as-yet unregistered 532 structured syntaxes should be used with care, given the possibility 533 of conflicts with future suffix definitions. 535 4.2.9. Deprecated Aliases 537 In some cases a single media type may have been widely deployed prior 538 to registrion under multiple names. In such cases a preferred name 539 MUST be chosen for the media type and applications MUST use this to 540 be compliant with the type's registration. However, a list of 541 deprecated aliases the type is known by MAY be supplied as additional 542 information in order to assist application in processing the media 543 type properly. 545 4.3. Parameter Requirements 547 Media types MAY elect to use one or more media type parameters, or 548 some parameters may be automatically made available to the media type 549 by virtue of being a subtype of a content type that defines a set of 550 parameters applicable to any of its subtypes. In either case, the 551 names, values, and meanings of any parameters MUST be fully specified 552 when a media type is registered in the standards tree, and SHOULD be 553 specified as completely as possible when media types are registered 554 in the vendor or personal trees. 556 Parameter names have the syntax as media type names and values: 558 parameter-name = restricted-name 560 Note that this syntax is somewhat more restrictive than what is 561 allowed by the ABNF in [RFC2045] and amended by [RFC2231]. 563 Parameter names are case-insensitive and no meaning is attached to 564 the order in which they appear. It is an error for a specific 565 parameter to be specified more than once. 567 There is no defined syntax for parameter values. Therefore 568 registrations MUST specify parameter value syntax. Additionally, 569 some transports impose restrictions on parameter value syntax, so 570 care should be taken to limit the use of potentially problematic 571 syntaxes; e.g., pure binary valued parameters, while permitted in 572 some protocols, probably should be avoided. 574 New parameters SHOULD NOT be defined as a way to introduce new 575 functionality in types registered in the standards tree, although new 576 parameters MAY be added to convey additional information that does 577 not otherwise change existing functionality. An example of this 578 would be a "revision" parameter to indicate a revision level of an 579 external specification such as JPEG. Similar behavior is encouraged 580 for media types registered in the vendor or personal trees, but is 581 not required. 583 4.4. Canonicalization and Format Requirements 585 All registered media types MUST employ a single, canonical data 586 format, regardless of registration tree. 588 A precise and openly available specification of the format of each 589 media type MUST exist for all types registered in the standards tree 590 and MUST at a minimum be referenced by, if it is not actually 591 included in, the media type registration proposal itself. 593 The specifications of format and processing particulars may or may 594 not be publicly available for media types registered in the vendor 595 and personal trees, and such registrations are explicitly permitted 596 to limit the information in the registration to which software and 597 version produce or process such media types. As such, teferences to 598 or inclusion of format specifications in registrations is encouraged 599 but not required. Note, however, that the public availability of a 600 meaningful specification will often make the difference between 601 simply having a name reserved so that there are no conflicts with 602 other uses and having the potential for other implementations of the 603 media type and useful interoperation with them. 605 Some media types involve the use of patented technology. The 606 registration of media types involving patented technology is 607 specifically permitted. However, the restrictions set forth in 608 [RFC3979] and [RFC5378] on the use of patented technology in IETF 609 standards-track protocols must be respected when the specification of 610 a media type is part of a standards-track protocol. In addition, 611 other standards bodies making use of the standards tree may have 612 their own rules regarding intellectual property that must be observed 613 in their registrations. 615 IPR disclosures for registrations in the vendor and personal tree are 616 encouraged but not required. 618 4.5. Interchange Recommendations 620 Media types SHOULD interoperate across as many systems and 621 applications as possible. However, some media types will inevitably 622 have problems interoperating across different platforms. Problems 623 with different versions, byte ordering, and specifics of gateway 624 handling can and will arise. 626 Universal interoperability of media types is not required, but known 627 interoperability issues SHOULD be identified whenever possible. 628 Publication of a media type does not require an exhaustive review of 629 interoperability, and the interoperability considerations section is 630 subject to continuing evaluation. 632 These recommendations in this subsection apply regardless of the 633 registration tree involved. 635 4.6. Security Requirements 637 An analysis of security issues MUST be done for all types registered 638 in the standards tree. A similar analysis for media types registered 639 in the vendor or personal trees is encouraged but not required. 640 However, regardless of what security analysis has or has not been 641 done, all descriptions of security issues MUST be as accurate as 642 possible regardless of registration tree. In particular, a statement 643 that there are "no security issues associated with this type" MUST 644 NOT be confused with "the security issues associates with this type 645 have not been assessed". 647 There is absolutely no requirement that media types registered in any 648 tree be secure or completely free from risks. Nevertheless, all 649 known security risks MUST be identified in the registration of a 650 media type, again regardless of registration tree. 652 The security considerations section of all registrations is subject 653 to continuing evaluation and modification, and in particular MAY be 654 extended by use of the "comments on media types" mechanism described 655 in Section 5.4 below. 657 Some of the issues that should be examined and described in a 658 security analysis of a media type are: 660 o Complex media types may include provisions for directives that 661 institute actions on a recipient's files or other resources. In 662 many cases provision is made for originators to specify arbitrary 663 actions in an unrestricted fashion that may then have devastating 664 effects. See the registration of the application/postscript media 665 type in [RFC2046] for an example of such directives and how they 666 should be described in a media type registration. 668 o All registrations MUST state whether or not they employ such 669 "active content", and if they do, they MUST state what steps have 670 been taken to protect users of the media type from harm. 672 o Complex media types may include provisions for directives that 673 institute actions that, while not directly harmful to the 674 recipient, may result in disclosure of information that either 675 facilitates a subsequent attack or else violates a recipient's 676 privacy in some way. Again, the registration of the application/ 677 postscript media type illustrates how such directives can be 678 handled. 680 o A media type that employs compression may provide an opportunity 681 for sending a small amount of data that, when received and 682 evaluated, expands enormously to consume all of the recipient's 683 resources. All media types SHOULD state whether or not they 684 employ compression, and if they do they should discuss what steps 685 need to be taken to avoid such attacks. 687 o A media type might be targeted for applications that require some 688 sort of security assurance but not provide the necessary security 689 mechanisms themselves. For example, a media type could be defined 690 for storage of sensitive medical information that in turn requires 691 an external confidentiality and integrity protection services, or 692 which is designed for use only within a secure environment. Types 693 not requiring such services SHOULD document this in their security 694 considerations. 696 4.7. Requirements specific to XML media types 698 There are a number of additional requirements specific to the 699 registration of XML media types. These requirements are specified in 700 [RFC3023]. 702 4.8. Encoding Requirements 704 Some transports impose restrictions on the type of data they can 705 carry. For example, Internet mail traditionally was limited to 7bit 706 US-ASCII text. Encoding schemes are often used to work around such 707 transport limitations. 709 It is therefore useful to note what sort of data a media type can 710 consist of as part of its registration. An "encoding considerations" 711 field is provided for this purpose. Possible values of this field 712 are: 714 7bit: The content of the media type consists solely of CRLF- 715 delimited 7bit US-ASCII text. 717 8bit: The content of the media type consists solely of CRLF- 718 delimited 8bit text. 720 binary: The content consists of an unrestricted sequence of octets. 722 framed: The content consists of a series of frames or packets 723 without internal framing or alignment indicators. Additional out- 724 of-band information is needed to interpret the data properly, 725 including but not necessarily limited to, knowledge of the 726 boundaries between successive frames and knowledge of the 727 transport mechanism. Note that media types of this sort cannot 728 simply be stored in a file or transported as a simple stream of 729 octets; therefore, such media types are unsuitable for use in many 730 traditional protocols. A commonly used transport with framed 731 encoding is the Real-time Transport Protocol, RTP. Additional 732 rules for framed encodings defined for transport using RTP are 733 given in [RFC4855]. 735 Additional restrictions on 7bit and 8bit text are given in Section 736 4.1.1 of [RFC2046]. 738 4.9. Usage and Implementation Non-requirements 740 In the asynchronous mail environment, where information on the 741 capabilities of the remote mail agent is frequently not available to 742 the sender, maximum interoperability is attained by restricting the 743 media types used to those "common" formats expected to be widely 744 implemented. This was asserted in the past as a reason to limit the 745 number of possible media types, and resulted in a registration 746 process with a significant hurdle and delay for those registering 747 media types. 749 However, the need for "common" media types does not require limiting 750 the registration of new media types. If a limited set of media types 751 is recommended for a particular application, that should be asserted 752 by a separate applicability statement specific for the application 753 and/or environment. 755 Therefore, universal support and implementation of a media type is 756 NOT a requirement for registration. However, if a media type is 757 explicitly intended for limited use, this MUST be noted in its 758 registration. The "Restrictions on Usage" field is provided for this 759 purpose. 761 4.10. Publication Requirements 763 Media types registered in the standards tree by the IETF itself MUST 764 be published as RFCs. RFC publication of vendor and personal media 765 type registrations is allowed but not required. In all cases the 766 IANA will retain copies of all media type registrations and "publish" 767 them as part of the media types registration tree itself. 769 As stated previously, standards tree registrations for media types 770 defined in documents produced by other standards bodies MUST be 771 described by a formal standards specification produced by that body. 772 Additionally, any copyright on the registration template MUST allow 773 the IANA to copy it into the IANA registry. 775 Other than IETF registrations in the standards tree, the registration 776 of a media type does not imply endorsement, approval, or 777 recommendation by the IANA or the IETF or even certification that the 778 specification is adequate. To become Internet Standards, a protocol 779 or data object must go through the IETF standards process. While it 780 provides additional assurances when it is appropriate, this is too 781 difficult and too lengthy a process for the convenient registration 782 of media types. 784 The standards tree exists for media types that do require a 785 substantive review and approval process in a recognized standards 786 body. The vendor and personal trees exist for those media types that 787 do not require such a process. It is expected that applicability 788 statements for particular applications will be published from time to 789 time in the IETF, recommending implementation of, and support for, 790 media types that have proven particularly useful in those contexts. 792 As discussed above, registration of a top-level type requires 793 standards-track processing in the IETF and, hence, RFC publication. 795 4.11. Additional Information 797 Various sorts of optional information SHOULD be included in the 798 specification of a media type if it is available: 800 o Magic number(s) (length, octet values). Magic numbers are byte 801 sequences that are always present at a given place in the file and 802 thus can be used to identify entities as being of a given media 803 type. 805 o File name extension(s) commonly used on one or more platforms to 806 indicate that some file contains a given media type. 808 o Mac OS File Type code(s) (4 octets) used to label files containing 809 a given media type. Some discussion of Macintosh file type codes 810 and their purpose can be found in [MacOSFileTypes]. 812 o Information about how fragment/anchor identifiers [RFC3986] are 813 constructed for use in conjunction with this media type. 815 In the case of a registration in the standards tree, this additional 816 information MAY be provided in the formal specification of the media 817 type. It is suggested that this be done by incorporating the IANA 818 media type registration form into the specification itself. 820 5. Media Type Registration Procedures 822 The media type registration procedure is not a formal standards 823 process, but rather an administrative procedure intended to allow 824 community comment and sanity checking without excessive time delay. 826 The normal IETF processes should be followed for all IETF 827 registrations in the standards tree. The posting of an Internet 828 Draft is a necessary first step, followed by posting to the 829 ietf-types@iana.org list as discussed below. 831 5.1. Preliminary Community Review 833 Notice of a potential media type registration in the standards tree 834 SHOULD be sent to the ietf-types@iana.org mailing list for review. 835 This mailing list has been established for the purpose of reviewing 836 proposed media and access types. Registrations in other trees MAY be 837 sent to the list for review as well; doing so is entirely OPTIONAL, 838 but is strongly encouraged. 840 The intent of the public posting to this list is to solicit comments 841 and feedback on the choice of type/subtype name, the unambiguity of 842 the references with respect to versions and external profiling 843 information, and a review of any interoperability or security 844 considerations. The submitter may submit a revised registration 845 proposal or abandon the registration completely and at any time. 847 5.2. Submit request to IANA 849 Media types registered in the standards tree by the IETF itself MUST 850 be reviewed and approved by the IESG as part of the normal standards 851 process. Standards tree registrations by recognized standards bodies 852 as well as registrations in the vendor and personal tree should be 853 submitted directly to the IANA, unless other arrangements were made 854 as part of a liaison agreement. In either case posting the 855 registration to the ietf-types@iana.org list for review prior to 856 submission is strongly encouraged. 858 Registration requests can be sent to iana@iana.org. A web form for 859 registration requests is also available: 861 http://www.iana.org/cgi-bin/mediatypes.pl 863 5.2.1. Provisional Registrations 865 Standardization processes often take considerable time to complete. 866 In order to facilitate prototyping and testing it is often helpful to 867 assign identifiers, including but not limited to media types, early 868 in the process. This way identifiers used during standards 869 development can remain unchanged once the process is complete and 870 implementations and documentation do not have to be updated. 872 Accordingly, a provisonal registration process is provided to support 873 early assigment of media type names. A provisional registration MAY 874 be submitted to IANA for standards tree types. The only required 875 fields in such registrations are the media type name and contact 876 information (inckuding the standards body name). 878 Upon receipt of a provisionl registration, IANA will check the name 879 and contact information, then publish the registration in a separate 880 provisional registration list. 882 Provisional registrations MAY be updated or abandoned at any time. 884 5.3. Review and Approval 886 With the exception of provisional standards tree registrations, 887 registrations submitted to the IANA will be passed on to the media 888 types reviewer. The media types reviewer, who is appointed by the 889 IETF Applications Area Director(s), will review the registration to 890 make sure it meets the requirements set forth in this document. 891 Registrations that do not meet these requirements will be returned to 892 the submitter for revision. 894 Decisions made by the media types reviewer may be appealed to the 895 IESG using the procedure specified in section 6.5.4 of [RFC2026]. 897 Once a media type registration has passed review, the IANA will 898 register the media type and make the media type registration 899 available to the community. 901 In the case of standards tree registrations from other standards 902 bodies IANA will also check that the submitter is in fact a 903 recognized standards body. If the submitter is not currently 904 recognized as such the IESG will be asked to confirm their status. 905 Recognition from the IESG MUST be obtained before a standards tree 906 registration can proceed. 908 5.4. Comments on Media Type Registrations 910 Comments on registered media types may be submitted by members of the 911 community to the IANA at iana@iana.org. These comments will be 912 reviewed by the media types reviewer and then passed on to the 913 "owner" of the media type if possible. Submitters of comments may 914 request that their comment be attached to the media type registration 915 itself, and if the IANA approves of this, the comment will be made 916 accessible in conjunction with the type registration. 918 5.5. Location of Registered Media Type List 920 Media type registrations are listed by the IANA at: 922 http://www.iana.org/assignments/media-types/ 924 5.6. Change Procedures 926 Once a media type has been published by the IANA, the owner may 927 request a change to its definition. The descriptions of the 928 different registration trees above designate the "owners" of each 929 type of registration. The same procedure that would be appropriate 930 for the original registration request is used to process a change 931 request. 933 Significant changes to a media type's definition should be requested 934 only when there are serious omissions or errors in the published 935 specification. When review is required, a change request may be 936 denied if it renders entities that were valid under the previous 937 definition invalid under the new definition. 939 The owner of a media type may pass responsibility to another person 940 or agency by informing the IANA; this can be done without discussion 941 or review. 943 The IESG may reassign responsibility for a media type. The most 944 common case of this will be to enable changes to be made to types 945 where the author of the registration has died, moved out of contact 946 or is otherwise unable to make changes that are important to the 947 community. 949 Media type registrations may not be deleted; media types that are no 950 longer believed appropriate for use can be declared OBSOLETE by a 951 change to their "intended use" field; such media types will be 952 clearly marked in the lists published by the IANA. 954 5.7. Registration Template 956 Type name: 958 Subtype name: 960 Required parameters: 962 Optional parameters: 964 Encoding considerations: 966 Security considerations: 968 Interoperability considerations: 970 Published specification: 972 Applications that use this media type: 974 Additional information: 976 Deprecated alias names for this type: 977 Magic number(s): 978 File extension(s): 979 Macintosh file type code(s): 980 URI fragment/anchor identifier(s): 982 Person & email address to contact for further information: 984 Intended usage: 986 (One of COMMON, LIMITED USE or OBSOLETE.) 988 Restrictions on usage: 990 (Any restrictions on where the media type can be used go here.) 992 Author: 994 Change controller: 996 Provisional registration? (standards tree only): 998 (Any other information that the author deems interesting may be 999 added below this line.) 1000 "N/A", written exactly that way, can be used in any field if desired 1001 to emphasize the fact that it does not apply or that the question was 1002 not omitted by accident. Do not use 'none' or other words that could 1003 be mistaken for a response. 1005 Limited use media types should also note in the applications list 1006 whether or not that list is exhaustive. 1008 6. Structured Syntax Suffix Registration Procedures 1010 Someone wishing to define a "+suffix" name for a structured syntax 1011 for use with a new media type registration SHOULD: 1013 1. Check IANA's registry of media type name suffixes to see whether 1014 or not there is already an entry for that well-defined structured 1015 syntax. 1017 2. If there is no entry for their suffix scheme, fill out the 1018 template (specified in Section 6.2) and include that with the 1019 media type registration. The template may be contained in an 1020 Internet Draft, alone or as part of some other protocol 1021 specification. The template may also be submitted in some other 1022 form (as part of another document or as a stand-alone document), 1023 but the contents will be treated as an "IETF Contribution" under 1024 the guidelines of RFC 5378 [RFC5378]. 1026 3. Send a copy of the template or a pointer to the containing 1027 document (with specific reference to the section with the 1028 template) to the mailing list ietf-types@ietf.org, requesting 1029 review. This may be combined with a request to review the media 1030 type registration. Allow a reasonable time for discussion and 1031 comments. 1033 4. Respond to review comments and make revisions to the proposed 1034 registration as needed to bring it into line with the guidelines 1035 given in this document. 1037 5. Submit the (possibly updated) registration template (or pointer 1038 to the document containing it) to IANA at iana@iana.org. 1040 Upon receipt of a structured syntax suffix registration request, 1042 1. IANA checks the submission for completeness; if sections are 1043 missing or citations are not correct, IANA rejects the 1044 registration request. 1046 2. IANA checks the current registry for an entry with the same name; 1047 if such a registry exists, IANA rejects the registration request. 1049 3. IANA requests Expert Review of the registration request against 1050 the corresponding guidelines. 1052 4. The Designated Expert may request additional review or 1053 discussion, as necessary. 1055 5. If Expert Review recommends registration, IANA adds the 1056 registration to the appropriate registry. 1058 6.1. Change Procedures 1060 Registrations may be updated in each registry by the same mechanism 1061 as required for an initial registration. In cases where the original 1062 definition of the scheme is contained in an IESG-approved document, 1063 update of the specification also requires IESG approval. 1065 6.2. Structured Syntax Suffix Registration Template 1067 This template describes the fields that must be supplied in a 1068 structured syntax sufficx registration request: 1070 Name 1071 Full name of the well-defined structured syntax. 1073 +suffix 1074 Suffix used to indicate conformance to the syntax. 1076 References. 1077 Include full citations for all specifications necessary to 1078 understand the structured syntax. 1080 Encoding considerations 1081 General guidance regarding encoding considerations for any type 1082 employing this syntax should be given here. The same requirements 1083 for media type encoding considerations given in Section 4.8 apply 1084 here. 1086 Interoperability considerations 1087 Any issues regarding the interoperable use of types employing this 1088 structured syntax should be given here. Examples would include 1089 the existence of incompatible versions of the syntax, issues 1090 combining certain charsets with the syntax, or incompatibilities 1091 with other types or protocols. 1093 Security considerations 1094 Security considerations shared by media types employing this 1095 structured syntax must be specified here. The same requirements 1096 for media type security considerations given in Section 4.6 apply 1097 here, with the exception that option of not assessing the security 1098 considerations is not available for suffix registrations. 1100 Contact 1101 Person (including contact information) to contact for further 1102 information. 1104 Author/Change controller. 1105 Person (including contact information) authorized to change this 1106 suffix registration. 1108 7. Security Considerations 1110 Security requirements for media type registrations are discussed in 1111 Section 4.6. 1113 8. IANA Considerations 1115 The purpose of this document is to define IANA registries for media 1116 types and structured syntax suffixes as well as the procedures for 1117 managing these registries. Additionally, this document requires IANA 1118 to maintain a list of IESG-recognized standards bodies who are 1119 allowed to register types in the standards tree. 1121 This document also creates a new registry for structured syntax 1122 names: 1124 o The name is the "Structured Syntax Suffix" registry. 1126 o The registration process is specified in Section 6. 1128 o The information required for a registry entry as well as the entry 1129 format are specified in Section 6.2. 1131 o The initial content of the registry shall be constructed at the 1132 time of the registry's creation by the designated media types 1133 reviewer(s) by examining the current media types registry and 1134 extracting all conforming uses of "+suffix" names. 1136 9. Acknowledgements 1138 The current authors would like to acknowledge their debt to the late 1139 Dr. Jon Postel, whose general model of IANA registration procedures 1140 and specific contributions shaped the predecessors of this document 1141 [RFC2048]. We hope that the current version is one with which he 1142 would have agreed but, as it is impossible to verify that agreement, 1143 we have regretfully removed his name as a co-author. 1145 Barry Leiba and Alexey Melnikov provided many helpful review comments 1146 and suggestions. 1148 10. References 1150 10.1. Normative References 1152 [I-D.ietf-appsawg-mime-default-charset] 1153 Melnikov, A. and J. Reschke, "Update to MIME regarding 1154 Charset Parameter Handling in Textual Media Types", 1155 draft-ietf-appsawg-mime-default-charset-00 (work in 1156 progress), February 2012. 1158 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1159 Extensions (MIME) Part One: Format of Internet Message 1160 Bodies", RFC 2045, November 1996. 1162 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1163 Extensions (MIME) Part Two: Media Types", RFC 2046, 1164 November 1996. 1166 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1167 Requirement Levels", BCP 14, RFC 2119, March 1997. 1169 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 1170 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 1171 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 1173 [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration 1174 Procedures", BCP 19, RFC 2978, October 2000. 1176 [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media 1177 Types", RFC 3023, January 2001. 1179 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1180 10646", STD 63, RFC 3629, November 2003. 1182 [RFC3979] Bradner, S., "Intellectual Property Rights in IETF 1183 Technology", BCP 79, RFC 3979, March 2005. 1185 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1186 Resource Identifier (URI): Generic Syntax", STD 66, 1187 RFC 3986, January 2005. 1189 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 1190 Formats", RFC 4855, February 2007. 1192 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1193 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1194 May 2008. 1196 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1197 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1199 [RFC5378] Bradner, S. and J. Contreras, "Rights Contributors Provide 1200 to the IETF Trust", BCP 78, RFC 5378, November 2008. 1202 [RFC6532] Yang, A., Steel, S., and N. Freed, "Internationalized 1203 Email Headers", RFC 6532, January 2012. 1205 10.2. Informative References 1207 [I-D.ietf-appsawg-xdash] 1208 Saint-Andre, P. and D. Crocker, "Deprecating the X- Prefix 1209 and Similar Constructs in Application Protocols", 1210 draft-ietf-appsawg-xdash-04 (work in progress), 1211 March 2012. 1213 [MacOSFileTypes] 1214 Apple Computer, Inc., "Mac OS: File Type and Creator 1215 Codes, and File Formats", Apple Knowledge Base Article 1216 55381, June 1993, 1217 . 1219 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 1220 3", BCP 9, RFC 2026, October 1996. 1222 [RFC2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose 1223 Internet Mail Extensions (MIME) Part Four: Registration 1224 Procedures", BCP 13, RFC 2048, November 1996. 1226 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded 1227 Word Extensions: 1228 Character Sets, Languages, and Continuations", RFC 2231, 1229 November 1997. 1231 Appendix A. Grandfathered Media Types 1233 A number of media types with unfaceted names, registered prior to 1234 1996, would, if registered under the guidelines in this document, be 1235 given a faceted name and placed into either the vendor or personal 1236 trees. Reregistration of those types to reflect the appropriate 1237 trees is encouraged but not required. Ownership and change control 1238 principles outlined in this document apply to those types as if they 1239 had been registered in the trees described above. 1241 From time to time there may also be cases where a media type with an 1242 unfaceted name has been widely deployed without being registered. 1243 (Note that this includes types with names beginning with the "x-" 1244 prefix.) If possible such types SHOULD be reregistered with a proper 1245 faceted name. However, if this is not possible the type can, subject 1246 to approval by both the media types reviewer and the IESG, be 1247 registered in the proper tree with its unfaceted name. 1249 Appendix B. Changes Since RFC 4288 1251 o Suffixes to indicate the use of a particular structured syntax are 1252 now fully specified and a suffix registration process has been 1253 defined. 1255 o Registration of widely deployed unregistered unfaceted type names 1256 in the vendor or personal trees is now allowed, subject to 1257 approval by the media types reviewer and the IESG. 1259 o The standards tree registration process has been revised to 1260 include Expert Review and generalized to address cases like media 1261 types in non-IETF stream documents. 1263 o A field for fragment/anchor identifiers has been added to the 1264 registration template. 1266 o The specification requirements for personal tree registrations 1267 have been changed to be the same as those for the vendor tree. 1268 The text has been changed to encourage (but not require) 1269 specification availability. 1271 o The definition of additional trees has been clarified to state 1272 that an IETF Standards Action is required. 1274 o Widely deployed types with "x-" names can now be registered as an 1275 exception in the vendor tree. 1277 o The reqiremeents on changes to registrations have been loosened so 1278 minor changes are easier to make. 1280 o The registration process has been completely restructured so that 1281 with the exception of IETF-generated types in the standards tree, 1282 all requests are procesed by IANA and not the IESG. 1284 o A provisional registration process has been added for early 1285 assignment of types in the standards tree. 1287 o Many editorial changes have been made throughout the document to 1288 make the requirements and processes it describes clearer and 1289 easier to follow. 1291 o The ability to specify a list of deprecated aliases has been 1292 added. 1294 o Types with names beginning with "x-" are no longer considered to 1295 be members of the unregistered "x." tree. As with any unfaceted 1296 type, special procedures have been added to allow registration of 1297 such types in an appropriate tree. 1299 o Changes to a type registered by a third party may now be made by 1300 the designated change controller even if that isn't the vendor or 1301 organization that created the type. However, the vendor or 1302 orgnanization may elect to assert ownership and change controler 1303 over the type at any time. 1305 o Limited use media types are now asked to note whether or not the 1306 supplied list of applications employing the media type is 1307 exhaustive. 1309 Authors' Addresses 1311 Ned Freed 1312 Oracle 1313 800 Royal Oaks 1314 Monrovia, CA 91016-6347 1315 USA 1317 Email: ned+ietf@mrochek.com 1318 John C. Klensin 1319 1770 Massachusetts Ave, #322 1320 Cambridge, MA 02140 1321 USA 1323 Email: john+ietf@jck.com 1325 Tony Hansen 1326 AT&T Laboratories 1327 200 Laurel Ave. 1328 Middletown, NJ 07748 1329 USA 1331 Email: tony+mtsuffix@maillennium.att.com