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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: September 13, 2012 6 T. Hansen 7 AT&T Laboratories 8 March 12, 2012 10 Media Type Specifications and Registration Procedures 11 draft-ietf-appsawg-media-type-regs-02 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 September 13, 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 . . . . . . . . . . . . . . . . . . 10 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 . . . . . . . . . . . . . . . . . . 12 75 4.3. Parameter Requirements . . . . . . . . . . . . . . . . . . 13 76 4.4. Canonicalization and Format Requirements . . . . . . . . . 13 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 . . . . . . . . . . . . . . 18 85 5.1. Preliminary Community Review . . . . . . . . . . . . . . . 19 86 5.2. Submit request to IANA . . . . . . . . . . . . . . . . . . 19 87 5.2.1. Provisional Registrations . . . . . . . . . . . . . . 19 88 5.3. Review and Approval . . . . . . . . . . . . . . . . . . . 20 89 5.4. Comments on Media Type Registrations . . . . . . . . . . . 20 90 5.5. Location of Registered Media Type List . . . . . . . . . . 20 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 . . . . . . . . . . . . . . . . . . . . . . . 25 100 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 101 10.1. Normative References . . . . . . . . . . . . . . . . . . . 26 102 10.2. Informative References . . . . . . . . . . . . . . . . . . 27 103 Appendix A. Grandfathered Media Types . . . . . . . . . . . . . . 27 104 Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 28 105 Appendix C. Changes Since RFC 4288 . . . . . . . . . . . . . . . 28 106 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 108 1. Introduction 110 Recent Internet protocols have been carefully designed to be easily 111 extensible in certain areas. In particular, many protocols, 112 including but not limited to HTTP [RFC2616] and MIME [RFC2045], are 113 capable of carrying arbitrary labeled content. A mechanism is needed 114 to label such content and a registration process is needed for these 115 labels, so that that the set of such values are defined in a 116 reasonably orderly, well-specified, and public manner. 118 This document defines media type specification and registration 119 procedures that use the Internet Assigned Numbers Authority (IANA) as 120 a central registry. 122 1.1. Historical Note 124 The media type registration process was initially defined for 125 registering media types for use in the context of the asynchronous 126 Internet mail environment. In this mail environment there is a need 127 to limit the number of possible media types, to increase the 128 likelihood of interoperability when the capabilities of the remote 129 mail system are not known. As media types are used in new 130 environments in which the proliferation of media types is not a 131 hindrance to interoperability, the original procedure proved 132 excessively restrictive and had to be generalized. This was 133 initially done in [RFC2048], but the procedure defined there was 134 still part of the MIME document set. The media type specification 135 and registration procedure has now been moved to this separate 136 document, to make it clear that it is independent of MIME. 138 It may be desirable to restrict the use of media types to specific 139 environments or to prohibit their use in other environments. This 140 revision incorporates such restrictions into media type registrations 141 in a systematic way. See Section 4.9 for additional discussion. 143 1.2. Conventions Used in This Document 145 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 146 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 147 document are to be interpreted as described in [RFC2119]. 149 This specification makes use of the Augmented Backus-Naur Form (ABNF) 150 [RFC5234] notation, including the core rules defined in Appendix A of 151 that document. 153 2. Media Type Registration Preliminaries 155 Registration of a new media type or types starts with the 156 construction of a registration proposal. Registration may occur 157 within several different registration trees that have different 158 requirements, as discussed below. In general, a new registration 159 proposal is circulated and reviewed in a fashion appropriate to the 160 tree involved. The media type is then registered if the proposal is 161 acceptable. The following sections describe the requirements and 162 procedures used for each of the different registration trees. 164 3. Registration Trees and Subtype Names 166 In order to increase the efficiency and flexibility of the 167 registration process, different structures of subtype names may be 168 registered to accommodate the different natural requirements for, 169 e.g., a subtype that will be recommended for wide support and 170 implementation by the Internet community, or a subtype that is used 171 to move files associated with proprietary software. The following 172 subsections define registration "trees" that are distinguished by the 173 use of faceted names, e.g., names of the form 174 "tree.subtree...subtype". Note that some media types defined prior 175 to this document do not conform to the naming conventions described 176 below. See Appendix A for a discussion of them. 178 3.1. Standards Tree 180 The standards tree is intended for types of general interest to the 181 Internet community. Registrations in the standards tree MUST be 182 either: 184 1. in the case of registrations in IETF specifications, approved 185 directly by the IESG, or 187 2. registered by a recognized standards body using the 188 "Specification Required" IANA registration policy [RFC5226] 189 (which implies Expert Review). 191 The first procedure is used for registering registrations from IETF 192 Consensus documents, or in rare cases when registering a 193 grandfathered (see Appendix A) and/or otherwise incomplete 194 registration is in the interest of the Internet community. 196 In the second case the IESG makes a one time decision on whether the 197 registration submitter represents a recognized standards body; after 198 that, a Media Types Reviewer (Designated Expert or a group of 199 Designated Experts) performs the Expert Review as specified in this 200 document. Subsequent submissions from the same source do not involve 201 the IESG. 203 In the case of registration for the IETF itself, the registration 204 proposal MUST be published as an IETF Consensus RFC, which can be on 205 the Standards Track, a BCP, Informational, or Experimental. In the 206 case of registrations for other recognized standards bodies, the 207 format MUST be described by a formal standards specification produced 208 by that body. 210 Registrations published in non-IETF RFC streams are allowed and 211 require IESG approval. 213 Standards-tree registration RFCs can either be standalone 214 "registration only" RFCs, or they can be incorporated into a more 215 general specification of some sort. 217 Media types in the standards tree are normally denoted by names that 218 are not explicitly faceted, i.e., do not contain period (".", full 219 stop) characters. 221 The "owner" of a media type registration in the standards tree is 222 assumed to be the standards body itself. Modification or alteration 223 of the specification uses the same level of processing (e.g., a 224 registration submitted on Standards Track can be revised in another 225 Standards Track RFC, but cannot be revised in an Informational RFC) 226 required for the initial registration. 228 Standards-tree registrations from recognized standards bodies may be 229 submitted directly to the IANA, where they will undergo Expert Review 230 [RFC5226] prior to approval. In this case, the Expert Reviewer(s) 231 will, among other things, ensure that the required specification 232 provides adequate documentation. 234 3.2. Vendor Tree 236 The vendor tree is used for media types associated with commercially 237 available products. "Vendor" and "producer" are construed very 238 broadly in this context and are considered equivalent. Note that 239 industry consortia as well as non-commercial entities that do not 240 qualify as recognized standards bodies can quite appropriately 241 register media types in the vendor tree. 243 A registration may be placed in the vendor tree by anyone who needs 244 to interchange files associated with some product or set of products. 245 However, the registration formally belongs to the vendor or 246 organization producing the software or file format being registered. 247 Changes to the specification will be made at their request, as 248 discussed in subsequent sections. 250 Registrations in the vendor tree will be distinguished by the leading 251 facet "vnd.". That may be followed, at the discretion of the 252 registrant, by either a media subtype name from a well-known producer 253 (e.g., "vnd.mudpie") or by an IANA-approved designation of the 254 producer's name that is followed by a media type or product 255 designation (e.g., vnd.bigcompany.funnypictures). 257 While public exposure and review of media types to be registered in 258 the vendor tree is not required, using the ietf-types@iana.org 259 mailing list for review is encouraged to improve the quality of those 260 specifications. Registrations in the vendor tree may be submitted 261 directly to the IANA, where they will undergo Expert Review [RFC5226] 262 prior to approval. 264 3.3. Personal or Vanity Tree 266 Registrations for media types created experimentally or as part of 267 products that are not distributed commercially may be registered in 268 the personal or vanity tree. The registrations are distinguished by 269 the leading facet "prs.". 271 The owner of "personal" registrations and associated specifications 272 is the person or entity making the registration, or one to whom 273 responsibility has been transferred as described below. 275 While public exposure and review of media types to be registered in 276 the personal tree is not required, using the ietf-types@iana.org 277 mailing list (see Section 5.1) for review is encouraged to improve 278 the quality of those specifications. Registrations in the personal 279 tree may be submitted directly to the IANA, where they will undergo 280 Expert Review [RFC5226] prior to approval. 282 3.4. Unregistered x. Tree 284 Subtype names with "x." as the first facet may be used for types 285 intended exclusively for use in private, local environments. Types 286 in this tree cannot be registered and are intended for use only with 287 the active agreement of the parties exchanging them. 289 However, with the simplified registration procedures described above 290 for vendor and personal trees, it should rarely, if ever, be 291 necessary to use unregistered types. Therefore, use of types in the 292 "x." tree is strongly discouraged. 294 Note that types with names beginning with "x-" are no longer 295 considered to members of this tree. Also note that if a generally 296 useful and widely deployed type incorrectly ends up with an "x-" name 297 prefix, it MAY be registered using its current name in an alternate 298 tree by following the procedure defined in Appendix A. 300 3.5. Additional Registration Trees 302 From time to time and as required by the community, new top-level 303 registration trees may be created by IETF Standards Action. It is 304 explicitly assumed that these trees may be created for external 305 registration and management by well-known permanent bodies; for 306 example, scientific societies may register media types specific to 307 the sciences they cover. In general, the quality of review of 308 specifications for one of these additional registration trees is 309 expected to be equivalent to registrations in the standards tree by a 310 recognized Standards Development Organization. When the IETF 311 performs such review, it needs to consider the greater expertise of 312 the requesting body with respect to the subject media type. 314 4. Registration Requirements 316 Media type registrations are all expected to conform to various 317 requirements laid out in the following sections. Note that 318 requirement specifics sometimes vary depending on the registration 319 tree, again as detailed in the following sections. 321 4.1. Functionality Requirement 323 Media types MUST function as an actual media format. Registration of 324 things that are better thought of as a transfer encoding, as a 325 charset, or as a collection of separate entities of another type, is 326 not allowed. For example, although applications exist to decode the 327 base64 transfer encoding [RFC2045], base64 cannot be registered as a 328 media type. 330 This requirement applies regardless of the registration tree 331 involved. 333 4.2. Naming Requirements 335 All registered media types MUST be assigned type and subtype names. 336 The combination of these names serves to uniquely identify the media 337 type, and the format of the subtype name identifies the registration 338 tree. Both type and subtype names are case-insensitive. 340 Type and subtype names beginning with "x-" are reserved for 341 experimental use and MUST NOT be registered. This parallels the 342 restriction on the x. tree, as discussed in Section 3.4. 344 Type and subtype names MUST conform to the following ABNF: 346 type-name = restricted-name 347 subtype-name = restricted-name 349 restricted-name = 1*127restricted-name-chars 350 restricted-name-chars = ALPHA / DIGIT / "!" / 351 "#" / "$" / "&" / "." / 352 "+" / "-" / "^" / "_" 354 Note that this syntax is somewhat more restrictive than what is 355 allowed by the ABNF in section 5.1 of [RFC2045]. Also note that 356 while this syntax allows names of up to 127 characters, 357 implementation limits may make such long names problematic. For this 358 reason the components of names SHOULD be limited to 64 characters. 360 Although the name syntax treates "+" as equivalent to any other 361 character, it is used in media type names to introduce a structured 362 syntax specificer suffix. Structured syntax suffix requirements are 363 specified in Section 4.2.8. 365 While it is possible for a given media type to be assigned additional 366 names, the use of different names to identify the same media type is 367 discouraged. 369 These requirements apply regardless of the registration tree 370 involved. 372 The choice of top-level type name MUST take into account the nature 373 of media type involved. New subtypes of top-level types MUST conform 374 to the restrictions of the top-level type, if any. The following 375 sections describe each of the initial set of top-level types and 376 their associated restrictions. Additionally, various protocols, 377 including but not limited to HTTP and MIME, MAY impose additional 378 restrictions on the media types they can transport. (See [RFC2046] 379 for additional information on the restrictions MIME imposes.) 381 4.2.1. Text Media Types 383 The "text" media type is intended for sending material that is 384 principally textual in form. 386 Many subtypes of text, notably including the subtype "text/plain", 387 which is a generic subtype for plain text defined in [RFC2046], 388 define a "charset" parameter. If a "charset" parameter is defined 389 for a particular subtype of text, it MUST be used to specify a 390 charset name defined in accordance to the procedures laid out in 391 [RFC2978]. 393 A "charset" parameter SHOULD NOT be specified when charset 394 information is transported inside the payload (e.g., as in "text/ 395 xml"). 397 If a "charset" parameter is specified, it SHOULD be a required 398 parameter, eliminating the options of specifying a default value. If 399 there is a strong reason for the parameter to be optional despite 400 this advice, each subtype MAY specify its own default value, or 401 alternately, it MAY specify that there is no default value. Finally, 402 the "UTF-8" charset [RFC3629] SHOULD be selected as the default. See 403 [I-D.ietf-appsawg-mime-default-charset] for additional information on 404 the use of "charset" parameters in conjunction with subtypes of text. 406 Plain text does not provide for or allow formatting commands, font 407 attribute specifications, processing instructions, interpretation 408 directives, or content markup. Plain text is seen simply as a linear 409 sequence of characters, possibly interrupted by line breaks or page 410 breaks. Plain text MAY allow the stacking of several characters in 411 the same position in the text. Plain text in scripts like Arabic and 412 Hebrew may also include facilities that allow the arbitrary mixing of 413 text segments with different writing directions. 415 Beyond plain text, there are many formats for representing what might 416 be known as "rich text". An interesting characteristic of many such 417 representations is that they are to some extent readable even without 418 the software that interprets them. It is useful to distinguish them, 419 at the highest level, from such unreadable data as images, audio, or 420 text represented in an unreadable form. In the absence of 421 appropriate interpretation software, it is reasonable to present 422 subtypes of "text" to the user, while it is not reasonable to do so 423 with most non-textual data. Such formatted textual data should be 424 represented using subtypes of "text". 426 4.2.2. Image Media Types 428 A media type of "image" indicates that the content specifies one or 429 more individual images. The subtype names the specific image format. 431 4.2.3. Audio Media Types 433 A media type of "audio" indicates that the content contains audio 434 data. 436 4.2.4. Video Media Types 438 A media type of "video" indicates that the content specifies a time- 439 varying-picture image, possibly with color and coordinated sound. 440 The term 'video' is used in its most generic sense, rather than with 441 reference to any particular technology or format, and is not meant to 442 preclude subtypes such as animated drawings encoded compactly. 444 Note that although in general this document strongly discourages the 445 mixing of multiple media in a single body, it is recognized that many 446 so-called video formats include a representation for synchronized 447 audio and/or text, and this is explicitly permitted for subtypes of 448 "video". 450 4.2.5. Application Media Types 452 The "application" media type is to be used for discrete data that do 453 not fit in any of the media types, and particularly for data to be 454 processed by some type of application program. This is information 455 that must be processed by an application before it is viewable or 456 usable by a user. Expected uses for the "application" media type 457 include but are not limited to file transfer, spreadsheets, 458 presentations, scheduling data, and languages for "active" 459 (computational) material. (The last, in particular, can pose 460 security problems that must be understood by implementors, and that 461 are considered in detail in the discussion of the "application/ 462 postscript" media type in [RFC2046].) 464 For example, a meeting scheduler might define a standard 465 representation for information about proposed meeting dates. An 466 intelligent user agent would use this information to conduct a dialog 467 with the user, and might then send additional material based on that 468 dialog. More generally, there have been several "active" languages 469 developed in which programs in a suitably specialized language are 470 transported to a remote location and automatically run in the 471 recipient's environment. Such applications may be defined as 472 subtypes of the "application" media type. 474 The subtype of "application" will often either be the name or include 475 part of the name of the application for which the data are intended. 476 This does not mean, however, that any application program name may 477 simply be used freely as a subtype of "application"; the subtype 478 needs to be registered. 480 4.2.6. Multipart and Message Media Types 482 Multipart and message are composite types, that is, they provide a 483 means of encapsulating zero or more objects, each labeled with its 484 own media type. 486 All subtypes of multipart and message MUST conform to the syntax 487 rules and other requirements specified in [RFC2046] and amended by 488 Section 3.5 of [RFC6532]. 490 4.2.7. Additional Top-level Types 492 In some cases a new media type may not "fit" under any currently 493 defined top-level content type. Such cases are expected to be quite 494 rare. However, if such a case does arise a new top-level type can be 495 defined to accommodate it. Such a definition MUST be done via 496 standards-track RFC; no other mechanism can be used to define 497 additional top-level content types. 499 4.2.8. Structured Syntax Name Suffixes 501 [RFC3023] defined the first such augmentation to the media type 502 definition to additionally specify the underlying structure of that 503 media type. To quote: 505 This document also standardizes a convention (using the suffix 506 '+xml') for naming media types ... when those media types 507 represent XML MIME (Multipurpose Internet Mail Extensions) 508 entities. 510 That is, it specified a suffix (in that case, "+xml") to be appended 511 to the base media type name. 513 Since this was published, the defacto practice has arisen for using 514 this suffix convention for other well-known structuring syntaxes. In 515 particular, media types have been registered with suffixes such as 516 "+der", "+fastinfoset" and "+json". This specification formalizes 517 this practice and sets up a registry for structured type name 518 suffixes. 520 The primary guideline for whether a structured type name suffix 521 should be registerable is that it be described by a readily-available 522 description, preferably within a document published by an established 523 standards organization, and for which there's a reference that can be 524 used in a References section of an RFC. 526 Media types that make use of a named structured syntax SHOULD use the 527 appropriate registered "+suffix" for that structured syntax when they 528 are registered. By the same token, media types MUST NOT be given 529 names incorporating suffixes for structured syntaxes they do not 530 actually employ. "+suffix" constructs for as-yet unregistered 531 structured syntaxes should be used with care, given the possibility 532 of conflicts with future suffix definitions. 534 4.2.9. Deprecated Aliases 536 In some cases a single media type may have been widely deployed prior 537 to registrion under multiple names. In such cases a preferred name 538 MUST be chosen for the media type and applications MUST use this to 539 be compliant with the type's registration. However, a list of 540 deprecated aliases the type is known by MAY be supplied as additional 541 information in order to assist application in processing the media 542 type properly. 544 4.3. Parameter Requirements 546 Media types MAY elect to use one or more media type parameters, or 547 some parameters may be automatically made available to the media type 548 by virtue of being a subtype of a content type that defines a set of 549 parameters applicable to any of its subtypes. In either case, the 550 names, values, and meanings of any parameters MUST be fully specified 551 when a media type is registered in the standards tree, and SHOULD be 552 specified as completely as possible when media types are registered 553 in the vendor or personal trees. 555 Parameter names have the syntax as media type names and values: 557 parameter-name = restricted-name 559 Note that this syntax is somewhat more restrictive than what is 560 allowed by the ABNF in [RFC2045] and amended by [RFC2231]. 562 Parameter names are case-insensitive and no meaning is attached to 563 the order in which they appear. It is an error for a specific 564 parameter to be specified more than once. 566 There is no defined syntax for parameter values. Therefore 567 registrations MUST specify parameter value syntax. Additionally, 568 some transports impose restrictions on parameter value syntax, so 569 care should be taken to limit the use of potentially problematic 570 syntaxes; e.g., pure binary valued parameters, while permitted in 571 some protocols, probably should be avoided. 573 New parameters SHOULD NOT be defined as a way to introduce new 574 functionality in types registered in the standards tree, although new 575 parameters MAY be added to convey additional information that does 576 not otherwise change existing functionality. An example of this 577 would be a "revision" parameter to indicate a revision level of an 578 external specification such as JPEG. Similar behavior is encouraged 579 for media types registered in the vendor or personal trees, but is 580 not required. 582 4.4. Canonicalization and Format Requirements 584 All registered media types MUST employ a single, canonical data 585 format, regardless of registration tree. 587 A precise and openly available specification of the format of each 588 media type MUST exist for all types registered in the standards tree 589 and MUST at a minimum be referenced by, if it is not actually 590 included in, the media type registration proposal itself. 592 The specifications of format and processing particulars may or may 593 not be publicly available for media types registered in the vendor 594 and personal trees, and such registrations are explicitly permitted 595 to limit the information in the registration to which software and 596 version produce or process such media types. References to or 597 inclusion of format specifications in registrations is encouraged but 598 not required. Note, however, that the public availability of a 599 meaningful specification will often make the difference between 600 simply having a name reserved so that there are no conflicts with 601 other uses and having the potential for other implementations of the 602 media type and useful interoperation with them. 604 Some media types involve the use of patented technology. The 605 registration of media types involving patented technology is 606 specifically permitted. However, the restrictions set forth in 607 [RFC3979] and [RFC5378] on the use of patented technology in IETF 608 standards-track protocols must be respected when the specification of 609 a media type is part of a standards-track protocol. In addition, 610 other standards bodies making use of the standards tree may have 611 their own rules regarding intellectual property that must be observed 612 in their registrations. 614 IPR disclosures for registrations in the vendor and personal tree are 615 encouraged but not required. 617 4.5. Interchange Recommendations 619 Media types SHOULD interoperate across as many systems and 620 applications as possible. However, some media types will inevitably 621 have problems interoperating across different platforms. Problems 622 with different versions, byte ordering, and specifics of gateway 623 handling can and will arise. 625 Universal interoperability of media types is not required, but known 626 interoperability issues SHOULD be identified whenever possible. 627 Publication of a media type does not require an exhaustive review of 628 interoperability, and the interoperability considerations section is 629 subject to continuing evaluation. 631 These recommendations in this subsection apply regardless of the 632 registration tree involved. 634 4.6. Security Requirements 636 An analysis of security issues MUST be done for all types registered 637 in the standards Tree. A similar analysis for media types registered 638 in the vendor or personal trees is encouraged but not required. 639 However, regardless of what security analysis has or has not been 640 done, all descriptions of security issues MUST be as accurate as 641 possible regardless of registration tree. In particular, a statement 642 that there are "no security issues associated with this type" MUST 643 NOT be confused with "the security issues associates with this type 644 have not been assessed". 646 There is absolutely no requirement that media types registered in any 647 tree be secure or completely free from risks. Nevertheless, all 648 known security risks MUST be identified in the registration of a 649 media type, again regardless of registration tree. 651 The security considerations section of all registrations is subject 652 to continuing evaluation and modification, and in particular MAY be 653 extended by use of the "comments on media types" mechanism described 654 in Section 5.4 below. 656 Some of the issues that should be examined and described in a 657 security analysis of a media type are: 659 o Complex media types may include provisions for directives that 660 institute actions on a recipient's files or other resources. In 661 many cases provision is made for originators to specify arbitrary 662 actions in an unrestricted fashion that may then have devastating 663 effects. See the registration of the application/postscript media 664 type in [RFC2046] for an example of such directives and how they 665 should be described in a media type registration. 667 o All registrations MUST state whether or not they employ such 668 "active content", and if they do, they MUST state what steps have 669 been taken to protect users of the media type from harm. 671 o Complex media types may include provisions for directives that 672 institute actions that, while not directly harmful to the 673 recipient, may result in disclosure of information that either 674 facilitates a subsequent attack or else violates a recipient's 675 privacy in some way. Again, the registration of the application/ 676 postscript media type illustrates how such directives can be 677 handled. 679 o A media type that employs compression may provide an opportunity 680 for sending a small amount of data that, when received and 681 evaluated, expands enormously to consume all of the recipient's 682 resources. All media types SHOULD state whether or not they 683 employ compression, and if they do they should discuss what steps 684 need to be taken to avoid such attacks. 686 o A media type might be targeted for applications that require some 687 sort of security assurance but not provide the necessary security 688 mechanisms themselves. For example, a media type could be defined 689 for storage of sensitive medical information that in turn requires 690 an external confidentiality and integrity protection services, or 691 which is designed for use only within a secure environment. Types 692 not requiring such services SHOULD document this in their security 693 considerations. 695 4.7. Requirements specific to XML media types 697 There are a number of additional requirements specific to the 698 registration of XML media types. These requirements are specified in 699 [RFC3023]. 701 4.8. Encoding Requirements 703 Some transports impose restrictions on the type of data they can 704 carry. For example, Internet mail traditionally was limited to 7bit 705 US-ASCII text. Encoding schemes are often used to work around such 706 transport limitations. 708 It is therefore useful to note what sort of data a media type can 709 consist of as part of its registration. An "encoding considerations" 710 field is provided for this purpose. Possible values of this field 711 are: 713 7bit: The content of the media type consists solely of CRLF- 714 delimited 7bit US-ASCII text. 716 8bit: The content of the media type consists solely of CRLF- 717 delimited 8bit text. 719 binary: The content consists of an unrestricted sequence of octets. 721 framed: The content consists of a series of frames or packets 722 without internal framing or alignment indicators. Additional out- 723 of-band information is needed to interpret the data properly, 724 including but not necessarily limited to, knowledge of the 725 boundaries between successive frames and knowledge of the 726 transport mechanism. Note that media types of this sort cannot 727 simply be stored in a file or transported as a simple stream of 728 octets; therefore, such media types are unsuitable for use in many 729 traditional protocols. A commonly used transport with framed 730 encoding is the Real-time Transport Protocol, RTP. Additional 731 rules for framed encodings defined for transport using RTP are 732 given in [RFC4855]. 734 Additional restrictions on 7bit and 8bit text are given in Section 735 4.1.1 of [RFC2046]. 737 4.9. Usage and Implementation Non-requirements 739 In the asynchronous mail environment, where information on the 740 capabilities of the remote mail agent is frequently not available to 741 the sender, maximum interoperability is attained by restricting the 742 media types used to those "common" formats expected to be widely 743 implemented. This was asserted in the past as a reason to limit the 744 number of possible media types, and resulted in a registration 745 process with a significant hurdle and delay for those registering 746 media types. 748 However, the need for "common" media types does not require limiting 749 the registration of new media types. If a limited set of media types 750 is recommended for a particular application, that should be asserted 751 by a separate applicability statement specific for the application 752 and/or environment. 754 Therefore, universal support and implementation of a media type is 755 NOT a requirement for registration. However, if a media type is 756 explicitly intended for limited use, this MUST be noted in its 757 registration. The "Restrictions on Usage" field is provided for this 758 purpose. 760 4.10. Publication Requirements 762 Media types registered in the standards tree by the IETF itself MUST 763 be published as RFCs. RFC publication of vendor and personal media 764 type registrations is allowed but not required. In all cases the 765 IANA will retain copies of all media type registrations and "publish" 766 them as part of the media types registration tree itself. 768 As stated previously, standards tree registrations for media types 769 defined in documents produced by other standards bodies MUST be 770 described by a formal standards specification produced by that body. 771 Additionally, any copyright on the registration template MUST allow 772 the IANA to copy it into the IANA registry. 774 Other than IETF registrations in the standards tree, the registration 775 of a media type does not imply endorsement, approval, or 776 recommendation by the IANA or the IETF or even certification that the 777 specification is adequate. To become Internet Standards, a protocol 778 or data object must go through the IETF standards process. While it 779 provides additional assurances when it is appropriate, this is too 780 difficult and too lengthy a process for the convenient registration 781 of media types. 783 The standards tree exists for media types that do require a 784 substantive review and approval process in a recognized standards 785 body. The vendor and personal trees exist for those media types that 786 do not require such a process. It is expected that applicability 787 statements for particular applications will be published from time to 788 time in the IETF, recommending implementation of, and support for, 789 media types that have proven particularly useful in those contexts. 791 As discussed above, registration of a top-level type requires 792 standards-track processing in the IETF and, hence, RFC publication. 794 4.11. Additional Information 796 Various sorts of optional information SHOULD be included in the 797 specification of a media type if it is available: 799 o Magic number(s) (length, octet values). Magic numbers are byte 800 sequences that are always present at a given place in the file and 801 thus can be used to identify entities as being of a given media 802 type. 804 o File name extension(s) commonly used on one or more platforms to 805 indicate that some file contains a given media type. 807 o Mac OS File Type code(s) (4 octets) used to label files containing 808 a given media type. Some discussion of Macintosh file type codes 809 and their purpose can be found in [MacOSFileTypes]. 811 o Information about how fragment/anchor identifiers [RFC3986] are 812 constructed for use in conjunction with this media type. 814 In the case of a registration in the standards tree, this additional 815 information MAY be provided in the formal specification of the media 816 type. It is suggested that this be done by incorporating the IANA 817 media type registration form into the specification itself. 819 5. Media Type Registration Procedures 821 The media type registration procedure is not a formal standards 822 process, but rather an administrative procedure intended to allow 823 community comment and sanity checking without excessive time delay. 825 The normal IETF processes should be followed for all IETF 826 registrations in the standards tree. The posting of an Internet 827 Draft is a necessary first step, followed by posting to the 828 ietf-types@iana.org list as discussed below. 830 5.1. Preliminary Community Review 832 Notice of a potential media type registration in the standards tree 833 SHOULD be sent to the ietf-types@iana.org mailing list for review. 834 This mailing list has been established for the purpose of reviewing 835 proposed media and access types. Registrations in other trees MAY be 836 sent to the list for review as well; doing so is entirely OPTIONAL, 837 but is strongly encouraged. 839 The intent of the public posting to this list is to solicit comments 840 and feedback on the choice of type/subtype name, the unambiguity of 841 the references with respect to versions and external profiling 842 information, and a review of any interoperability or security 843 considerations. The submitter may submit a revised registration 844 proposal or abandon the registration completely and at any time. 846 5.2. Submit request to IANA 848 Media types registered in the standards tree by the IETF itself MUST 849 be reviewed and approved by the IESG as part of the normal standards 850 process. Standards tree registrations by recognized standards bodies 851 as well as registrations in the vendor and personal tree should be 852 submitted directly to the IANA, unless other arrangements were made 853 as part of a liaison agreement. In either case posting the 854 registration to the ietf-types@iana.org list for review prior to 855 submission is strongly encouraged. 857 Registration requests can be sent to iana@iana.org. A web form for 858 registration requests is also available: 860 http://www.iana.org/cgi-bin/mediatypes.pl 862 5.2.1. Provisional Registrations 864 Standardization processes often take considerable time to complete. 865 In order to facilitate prototyping and testing it is often helpful to 866 assign identifiers, including but not limited to media types, early 867 in the process. This way identifiers used during standards 868 development can remain unchanged once the process is complete and 869 implementations and documentation do not have to be updated. 871 Accordingly, a provisonal registration process is provided to support 872 early assigment of media type names. A provisional registration MAY 873 be submitted to IANA for standards tree types. The only required 874 fields in such registrations are the media type name and contact 875 information (inckuding the standards body name). 877 Upon receipt of a provisionl registration, IANA will check the name 878 and contact information, then publish the registration in a separate 879 provisional registration list. 881 Provisional registrations MAY be updated or abandoned at any time. 883 5.3. Review and Approval 885 With the exception of provisional standards tree registrations, 886 registrations submitted to the IANA will be passed on to the media 887 types reviewer. The media types reviewer, who is appointed by the 888 IETF Applications Area Director(s), will review the registration to 889 make sure it meets the requirements set forth in this document. 890 Registrations that do not meet these requirements will be returned to 891 the submitter for revision. 893 Decisions made by the media types reviewer may be appealed to the 894 IESG using the procedure specified in section 6.5.4 of [RFC2026]. 896 Once a media type registration has passed review, the IANA will 897 register the media type and make the media type registration 898 available to the community. 900 In the case of standards tree registrations from other standards 901 bodies IANA will also check that the submitter is in fact a 902 recognized standards body. If the submitter is not currently 903 recognized as such the IESG will be asked to confirm their status. 904 Recognition from the IESG MUST be obtained before a standards tree 905 registration can proceed. 907 5.4. Comments on Media Type Registrations 909 Comments on registered media types may be submitted by members of the 910 community to the IANA at iana@iana.org. These comments will be 911 reviewed by the media types reviewer and then passed on to the 912 "owner" of the media type if possible. Submitters of comments may 913 request that their comment be attached to the media type registration 914 itself, and if the IANA approves of this, the comment will be made 915 accessible in conjunction with the type registration. 917 5.5. Location of Registered Media Type List 919 Media type registrations are listed by the IANA at: 921 http://www.iana.org/assignments/media-types/ 923 5.6. Change Procedures 925 Once a media type has been published by the IANA, the owner may 926 request a change to its definition. The descriptions of the 927 different registration trees above designate the "owners" of each 928 type of registration. The same procedure that would be appropriate 929 for the original registration request is used to process a change 930 request. 932 Significant changes to a media type's definition should be requested 933 only when there are serious omissions or errors in the published 934 specification. When review is required, a change request may be 935 denied if it renders entities that were valid under the previous 936 definition invalid under the new definition. 938 The owner of a media type may pass responsibility to another person 939 or agency by informing the IANA; this can be done without discussion 940 or review. 942 The IESG may reassign responsibility for a media type. The most 943 common case of this will be to enable changes to be made to types 944 where the author of the registration has died, moved out of contact 945 or is otherwise unable to make changes that are important to the 946 community. 948 Media type registrations may not be deleted; media types that are no 949 longer believed appropriate for use can be declared OBSOLETE by a 950 change to their "intended use" field; such media types will be 951 clearly marked in the lists published by the IANA. 953 5.7. Registration Template 955 Type name: 957 Subtype name: 959 Required parameters: 961 Optional parameters: 963 Encoding considerations: 965 Security considerations: 967 Interoperability considerations: 969 Published specification: 971 Applications that use this media type: 973 Additional information: 975 Deprecated alias names for this type: 976 Magic number(s): 977 File extension(s): 978 Macintosh file type code(s): 979 URI fragment/anchor identifier(s): 981 Person & email address to contact for further information: 983 Intended usage: 985 (One of COMMON, LIMITED USE or OBSOLETE.) 987 Restrictions on usage: 989 (Any restrictions on where the media type can be used go here.) 991 Author: 993 Change controller: 995 Provisional registration? (standards tree only): 997 (Any other information that the author deems interesting may be 998 added below this line.) 999 "'N/A', written exactly that way, can be used in any field if desired 1000 to emphasize the fact that it does not apply or that the question was 1001 not omitted by accident. Do not use 'none' or other words that could 1002 be mistaken for a response". 1004 6. Structured Syntax Suffix Registration Procedures 1006 Someone wishing to define a "+suffix" name for a structured syntax 1007 for use with a new media type registration SHOULD: 1009 1. Check IANA's registry of media type name suffixes to see whether 1010 or not there is already an entry for that well-defined structured 1011 syntax. 1013 2. If there is no entry for their suffix scheme, fill out the 1014 template (specified in Section 6.2) and include that with the 1015 media type registration. The template may be contained in an 1016 Internet Draft, alone or as part of some other protocol 1017 specification. The template may also be submitted in some other 1018 form (as part of another document or as a stand-alone document), 1019 but the contents will be treated as an "IETF Contribution" under 1020 the guidelines of RFC 5378 [RFC5378]. 1022 3. Send a copy of the template or a pointer to the containing 1023 document (with specific reference to the section with the 1024 template) to the mailing list ietf-types@ietf.org, requesting 1025 review. This may be combined with a request to review the media 1026 type registration. Allow a reasonable time for discussion and 1027 comments. 1029 4. Respond to review comments and make revisions to the proposed 1030 registration as needed to bring it into line with the guidelines 1031 given in this document. 1033 5. Submit the (possibly updated) registration template (or pointer 1034 to the document containing it) to IANA at iana@iana.org. 1036 Upon receipt of a structured syntax suffix registration request, 1038 1. IANA checks the submission for completeness; if sections are 1039 missing or citations are not correct, IANA rejects the 1040 registration request. 1042 2. IANA checks the current registry for an entry with the same name; 1043 if such a registry exists, IANA rejects the registration request. 1045 3. IANA requests Expert Review of the registration request against 1046 the corresponding guidelines. 1048 4. The Designated Expert may request additional review or 1049 discussion, as necessary. 1051 5. If Expert Review recommends registration, IANA adds the 1052 registration to the appropriate registry. 1054 6.1. Change Procedures 1056 Registrations may be updated in each registry by the same mechanism 1057 as required for an initial registration. In cases where the original 1058 definition of the scheme is contained in an IESG-approved document, 1059 update of the specification also requires IESG approval. 1061 6.2. Structured Syntax Suffix Registration Template 1063 This template describes the fields that must be supplied in a 1064 structured syntax sufficx registration request: 1066 Name 1067 Full name of the well-defined structured syntax. 1069 +suffix 1070 Suffix used to indicate conformance to the syntax. 1072 References. 1073 Include full citations for all specifications necessary to 1074 understand the structured syntax. 1076 Encoding considerations 1077 General guidance regarding encoding considerations for any type 1078 employing this syntax should be given here. The same requirements 1079 for media type encoding considerations given in Section 4.8 apply 1080 here. 1082 Interoperability considerations 1083 Any issues regarding the interoperable use of types employing this 1084 structured syntax should be given here. Examples would include 1085 the existence of incompatible versions of the syntax, issues 1086 combining certain charsets with the syntax, or incompatibilities 1087 with other types or protocols. 1089 Security considerations 1090 Security considerations shared by media types employing this 1091 structured syntax must be specified here. The same requirements 1092 for media type security considerations given in Section 4.6 apply 1093 here, with the exception that option of not assessing the security 1094 considerations is not available for suffix registrations. 1096 Contact 1097 Person (including contact information) to contact for further 1098 information. 1100 Author/Change controller. 1101 Person (including contact information) authorized to change this 1102 suffix registration. 1104 7. Security Considerations 1106 Security requirements for media type registrations are discussed in 1107 Section 4.6. 1109 8. IANA Considerations 1111 The purpose of this document is to define IANA registries for media 1112 types and structured syntax suffixes as well as the procedures for 1113 managing these registries. Additionally, this document requires IANA 1114 to maintain a list of IESG-recognized standards bodies who are 1115 allowed to register types in the standards tree. 1117 This document also creates a new registry for structured syntax 1118 names: 1120 o The name is the "Structured Syntax Suffix" registry. 1122 o The registration process is specified in Section 6. 1124 o The information required for a registry entry as well as the entry 1125 format are specified in Section 6.2. 1127 o The initial content of the registry shall be constructed at the 1128 time of the registry's creation by the designated media types 1129 reviewer(s) by examining the current media types registry and 1130 extracting all conforming uses of "+suffix" names. 1132 9. Acknowledgements 1134 The current authors would like to acknowledge their debt to the late 1135 Dr. Jon Postel, whose general model of IANA registration procedures 1136 and specific contributions shaped the predecessors of this document 1137 [RFC2048]. We hope that the current version is one with which he 1138 would have agreed but, as it is impossible to verify that agreement, 1139 we have regretfully removed his name as a co-author. 1141 Barry Leiba and Alexey Melnikov provided many helpful review comments 1142 and suggestions. 1144 10. References 1146 10.1. Normative References 1148 [I-D.ietf-appsawg-mime-default-charset] 1149 Melnikov, A. and J. Reschke, "Update to MIME regarding 1150 Charset Parameter Handling in Textual Media Types", 1151 draft-ietf-appsawg-mime-default-charset-00 (work in 1152 progress), February 2012. 1154 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1155 Extensions (MIME) Part One: Format of Internet Message 1156 Bodies", RFC 2045, November 1996. 1158 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1159 Extensions (MIME) Part Two: Media Types", RFC 2046, 1160 November 1996. 1162 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1163 Requirement Levels", BCP 14, RFC 2119, March 1997. 1165 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 1166 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 1167 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 1169 [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration 1170 Procedures", BCP 19, RFC 2978, October 2000. 1172 [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media 1173 Types", RFC 3023, January 2001. 1175 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1176 10646", STD 63, RFC 3629, November 2003. 1178 [RFC3979] Bradner, S., "Intellectual Property Rights in IETF 1179 Technology", BCP 79, RFC 3979, March 2005. 1181 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1182 Resource Identifier (URI): Generic Syntax", STD 66, 1183 RFC 3986, January 2005. 1185 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 1186 Formats", RFC 4855, February 2007. 1188 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1189 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1190 May 2008. 1192 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1193 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1195 [RFC5378] Bradner, S. and J. Contreras, "Rights Contributors Provide 1196 to the IETF Trust", BCP 78, RFC 5378, November 2008. 1198 [RFC6532] Yang, A., Steel, S., and N. Freed, "Internationalized 1199 Email Headers", RFC 6532, January 2012. 1201 10.2. Informative References 1203 [MacOSFileTypes] 1204 Apple Computer, Inc., "Mac OS: File Type and Creator 1205 Codes, and File Formats", Apple Knowledge Base Article 1206 55381, June 1993, 1207 . 1209 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 1210 3", BCP 9, RFC 2026, October 1996. 1212 [RFC2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose 1213 Internet Mail Extensions (MIME) Part Four: Registration 1214 Procedures", BCP 13, RFC 2048, November 1996. 1216 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded 1217 Word Extensions: 1218 Character Sets, Languages, and Continuations", RFC 2231, 1219 November 1997. 1221 Appendix A. Grandfathered Media Types 1223 A number of media types with unfaceted names, registered prior to 1224 1996, would, if registered under the guidelines in this document, be 1225 given a faceted name and placed into either the vendor or personal 1226 trees. Reregistration of those types to reflect the appropriate 1227 trees is encouraged but not required. Ownership and change control 1228 principles outlined in this document apply to those types as if they 1229 had been registered in the trees described above. 1231 From time to time there may also be cases where a media type with an 1232 unfaceted name has been widely deployed without being registered. 1233 (Note that this includes types with names beginning with the "x-" 1234 prefix.) If possible such types SHOULD be reregistered with a proper 1235 faceted name. However, if this is not possible the type can, subject 1236 to approval by both the media types reviewer and the IESG, be 1237 registered in the proper tree with its unfaceted name. 1239 Appendix B. Open Issues 1241 o The list of fields in the registration is getting long. Should 1242 the fields be numbered and referred to by number in order to 1243 facilitate translation into other languages and similar 1244 activities? 1246 o Currently anyone can register a vendor media type on behalf of a 1247 vendor but subsequent to that only the vendor can make changes. 1248 Do we want to retain this restriction? 1250 o Should we add a field to the registration template where limited- 1251 use media types can provide an explicit list of the applications 1252 that employ that type? 1254 Appendix C. Changes Since RFC 4288 1256 o Suffixes to indicate the use of a particular structured syntax are 1257 now fully specified and a suffix registration process has been 1258 defined. 1260 o Registration of widely deployed unregistered unfaceted type names 1261 in the vendor or personal trees is now allowed, subject to 1262 approval by the media types reviewer and the IESG. 1264 o The standards tree registration process has been revised to 1265 include Expert Review and generalized to address cases like media 1266 types in non-IETF stream documents. 1268 o A field for fragment/anchor identifiers has been added to the 1269 registration template. 1271 o The specification requirements for personal tree registrations 1272 have been changed to be the same as those for the vendor tree. 1273 The text has been changed to encourage (but not require) 1274 specification availability. 1276 o The definition of additional trees has been clarified to state 1277 that an IETF Standards Action is required. 1279 o Widely deployed types with "X-" names can now be registered as an 1280 exception in the vendor tree. 1282 o The reqiremeents on changes to registrations have been loosened so 1283 minor changes are easier to make. 1285 o The registration process has been completely restructured so that 1286 with the exception of IETF-generated types in the standards tree, 1287 all requests are procesed by IANA and not the IESG. 1289 o A provisional registration process has been added for early 1290 assignment of types in the standards tree. 1292 o Many editorial changes have been made throughout the document to 1293 make the requirements and processes it describes clearer and 1294 easier to follow. 1296 o Added the ability to specify a list of deprecated aliases. 1298 o Types with names beginning with "x-" are no longer considered to 1299 be members of the unregistered "x." tree. As with any unfaceted 1300 type, special procedures have been added to allow registration of 1301 such types in an appropriate tree. 1303 Authors' Addresses 1305 Ned Freed 1306 Oracle 1307 800 Royal Oaks 1308 Monrovia, CA 91016-6347 1309 USA 1311 Email: ned+ietf@mrochek.com 1313 John C. Klensin 1314 1770 Massachusetts Ave, #322 1315 Cambridge, MA 02140 1316 USA 1318 Email: john+ietf@jck.com 1319 Tony Hansen 1320 AT&T Laboratories 1321 200 Laurel Ave. 1322 Middletown, NJ 07748 1323 USA 1325 Email: tony+mtsuffix@maillennium.att.com