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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-03) exists of draft-gellens-slim-negotiating-human-language-02 Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IETF N. Tomkinson 3 Internet-Draft N. Borenstein 4 Intended status: Standards Track Mimecast Ltd 5 Expires: January 21, 2017 July 20, 2016 7 Multiple Language Content Type 8 draft-ietf-slim-multilangcontent-02 10 Abstract 12 This document defines an addition to the Multipurpose Internet Mail 13 Extensions (MIME) standard to make it possible to send one message 14 that contains multiple language versions of the same information. 15 The translations would be identified by a language tag and selected 16 by the email client based on a user's language settings. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on January 21, 2017. 35 Copyright Notice 37 Copyright (c) 2016 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 1. Introduction 52 Since the invention of email and the rapid spread of the Internet, 53 more and more people have been able to communicate in more and more 54 countries and in more and more languages. But during this time of 55 technological evolution, email has remained a single-language 56 communication tool, whether it is English to English, Spanish to 57 Spanish or Japanese to Japanese. 59 Also during this time, many corporations have established their 60 offices in multi-cultural cities and formed departments and teams 61 that span continents, cultures and languages, so the need to 62 communicate efficiently with little margin for miscommunication has 63 grown exponentially. 65 The objective of this document is to define an addition to the 66 Multipurpose Internet Mail Extensions (MIME) standard, to make it 67 possible to send a single message to a group of people in such a way 68 that all of the recipients can read the email in their preferred 69 language. The methods of translation of the message content are 70 beyond the scope of this document, but the structure of the email 71 itself is defined herein. 73 Whilst this document depends on identification of language in message 74 parts for non-real-time communication, there is a companion document 75 that is concerned with a similar problem for real-time communication: 76 [I-D.gellens-slim-negotiating-human-language] 78 1.1. Requirements Language 80 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 81 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 82 document are to be interpreted as described in RFC 2119 [RFC2119]. 84 2. The Content-Type Header Field 86 The "multipart/multilingual" MIME subtype allows the sending of a 87 message in a number of different languages with the translations 88 embedded in the same message. This MIME subtype helps the receiving 89 email client make sense of the message structure. 91 The multipart subtype "multipart/multilingual" has similar semantics 92 to "multipart/alternative" (as discussed in RFC 2046 [RFC2046]) in 93 that each of the message parts is an alternative version of the same 94 information. The primary difference between "multipart/multilingual" 95 and "multipart/alternative" is that when using "multipart/ 96 multilingual", the message part to select for rendering is chosen 97 based on the values of the Content-Language field and optionally the 98 Translation-Type parameter of the Content-Language field instead of 99 the ordering of the parts and the Content-Types. 101 The syntax for this multipart subtype conforms to the common syntax 102 for subtypes of multipart given in section 5.1.1. of RFC 2046 103 [RFC2046]. An example "multipart/multilingual" Content-Type header 104 field would look like this: 106 Content-Type: multipart/multilingual; boundary=01189998819991197253 108 3. The Message Parts 110 A multipart/multilingual message will have a number of message parts: 111 exactly one multilingual preface, one or more language message parts 112 and zero or one language independent message part. The details of 113 these are described below. 115 3.1. The Multilingual Preface 117 In order for the message to be received and displayed in non- 118 conforming email clients, the message SHOULD contain an explanatory 119 message part which MUST NOT be marked with a Content-Language field 120 and MUST be the first of the message parts. For maximum support in 121 the most basic of non-conforming email clients, it SHOULD have a 122 Content-Type of text/plain. Because non-conforming email clients are 123 expected to treat a message with an unknown multipart type as 124 multipart/mixed (in accordance with sections 5.1.3 and 5.1.7 of RFC 125 2046 [RFC2046]) they may show all of the message parts sequentially 126 or as attachments. Including and showing this explanatory part will 127 help the message recipient understand the message structure. 129 This initial message part SHOULD explain briefly to the recipient 130 that the message contains multiple languages and the parts may be 131 rendered sequentially or as attachments. This SHOULD be presented in 132 the same languages that are provided in the subsequent language 133 message parts. 135 As this explanatory section is likely to contain languages using 136 scripts that require non-US-ASCII characters, it is RECOMMENDED that 137 UTF-8 encoding is used for this message part. 139 Whilst this section of the message is useful for backward 140 compatibility, it will normally only be shown when rendered by a non- 141 conforming email client, because conforming email clients SHOULD only 142 show the single language message part identified by the user's 143 preferred language and the language message part's Content-Language. 145 For the correct display of the multilingual preface in a non- 146 conforming email client, the sender MAY use the Content-Disposition 147 field with a value of 'inline' in conformance with RFC 2183 [RFC2183] 148 (which defines the Content-Disposition field). If provided, this 149 SHOULD be placed at the multipart/multilingual level and in the 150 multilingual preface. This makes it clear to a non-conforming email 151 client that the multilingual preface should be displayed immediately 152 to the recipient, followed by any subsequent parts marked as 153 'inline'. 155 For an example of a multilingual preface, see the examples in 156 Section 8. 158 3.2. The Language Message Parts 160 The language message parts are typically translations of the same 161 message content. These message parts SHOULD be ordered so that the 162 first part after the multilingual preface is in the language believed 163 to be the most likely to be recognised by the recipient as this will 164 constitute the default part when language negotiation fails and there 165 is no Language Independent part. All of the language message parts 166 MUST have a Content-Language field and a Content-Type field and MAY 167 have a Translation-Type parameter applied to the Content-Language 168 field. 170 The Content-Type for each individual language message part SHOULD be 171 message/rfc822 to provide good support with non-conforming email 172 clients. However, an implementation MAY use message/global as 173 support for message/global becomes more commonplace. Each language 174 message part SHOULD have a Subject field in the appropriate language 175 for that language part and SHOULD NOT have a From field. 177 3.3. The Language Independent Message Part 179 If there is language independent content intended for the recipient 180 to see if they have a preferred language other than one of those 181 specified in the language message parts and the default language 182 message part is unlikely to be understood, another part MAY be 183 provided. This could typically be a language independent graphic. 184 When this part is present, it MUST be the last part, MUST have a 185 Content-Language field with a value of "zxx" (as described in BCP 47/ 186 RFC 5646 [RFC5646]) and SHOULD NOT have a Subject field and SHOULD 187 NOT have a From field. The part SHOULD have a Content-Type of 188 message/rfc822 or message/global (to match the language message 189 parts). 191 4. Message Part Selection 193 The logic for selecting the message part to render and present to the 194 recipient is summarised in the next few paragraphs. 196 Firstly, if the email client does not understand multipart/ 197 multilingual then it SHOULD treat the message as if it was multipart/ 198 mixed and render message parts accordingly. 200 If the email client does understand multipart/multilingual then it 201 SHOULD ignore the multilingual preface and select the best match for 202 the user's preferred language from the language message parts 203 available. Also, the user may prefer to see the original message 204 content in their second language over a machine translation in their 205 first language. The Translation-Type parameter of the Content- 206 Language field value can be used for further selection based on this 207 preference. The selection of language part may be implemented in a 208 variety of ways, although the matching schemes detailed in RFC 4647 209 [RFC4647] are RECOMMENDED as a starting point for an implementation. 210 The goal is to render the most appropriate translation for the user. 212 If there is no match for the user's preferred language (or there is 213 no preferred language information available) the email client SHOULD 214 select the language independent part (if one exists) or the first 215 language part (directly after the multilingual preface) if a language 216 independent part does not exist. 218 If there is no translation type preference information available, the 219 values of the Translation-Type parameter may be ignored. 221 Additionally, interactive implementations MAY offer the user a choice 222 from among the available languages. 224 5. The Content-Language Field 226 The Content-Language field in the individual language message parts 227 is used to identify the language in which the message part is 228 written. Based on the value of this field, a conforming email client 229 can determine which message part to display (given the user's 230 language settings). 232 The Content-Language MUST comply with RFC 3282 [RFC3282] (which 233 defines the Content-Language field) and BCP 47/RFC 5646 [RFC5646] 234 (which defines the structure and semantics for the language code 235 values). While RFC 5646 provides a mechanism accommodating 236 increasingly fine-grained distinctions, in the interest of maximum 237 interoperability, each Content-Language value SHOULD be restricted to 238 the largest granularity of language tags; in other words, it is 239 RECOMMENDED to specify only a Primary-subtag and NOT to include 240 subtags (e.g., for region or dialect) unless the languages might be 241 mutually incomprehensible without them. Examples of this field for 242 English, German and an instruction manual in Spanish and French, 243 could look like the following: 245 Content-Language: en 247 Content-Language: de 249 Content-Language: es, fr 251 6. The Translation-Type Parameter 253 The Translation-Type parameter can be applied to the Content-Language 254 field in the individual language message parts and is used to 255 identify the type of translation. Based on the value of this 256 parameter and the user's preferences, a conforming email client can 257 determine which message part to display. 259 This parameter can have one of three possible values: 'original', 260 'human' or 'automated' although other values may be added in the 261 future. A value of 'original' is given in the language message part 262 that is in the original language. A value of 'human' is used when a 263 language message part is translated by a human translator or a human 264 has checked and corrected an automated translation. A value of 265 'automated' is used when a language message part has been translated 266 by an electronic agent without proofreading or subsequent correction. 268 Examples of this parameter include: 270 Content-Language: en; translation-type=original 272 Content-Language: fr; translation-type=human 274 7. The Subject Field in the Language Message parts 276 On receipt of the message, conforming email clients will need to 277 render the subject in the correct language for the recipient. To 278 enable this the Subject field SHOULD be provided in each language 279 message part. The value for this field should be a translation of 280 the email subject. 282 US-ASCII and 'encoded-word' examples of this field include: 284 Subject: A really simple email subject 285 Subject: =?UTF-8?Q?Un_asunto_de_correo_electr=C3=b3nico_ 286 realmente_sencillo?= 288 See RFC 2047 [RFC2047] for the specification of 'encoded-word'. 290 The subject to be presented to the recipient should be selected from 291 the message part identified during the message part selection stage. 292 If no Subject field is found (for example if the language independent 293 part is selected) the top-level Subject header field value should be 294 used. 296 8. Examples 298 8.1. An Example of a Simple Multiple language email message 300 Below is a minimal example of a multiple language email message. It 301 has the multilingual preface and two language message parts. 303 From: Nik 304 To: Nathaniel 305 Subject: Example of a message in Spanish and English 306 Date: Thu, 7 Jul 2016 21:28:00 +0100 307 MIME-Version: 1.0 308 Content-Type: multipart/multilingual; 309 boundary="01189998819991197253" 311 --01189998819991197253 312 Content-Type: text/plain; charset="UTF-8" 313 Content-Disposition: inline 314 Content-Transfer-Encoding: quoted-printable 316 This is a message in multiple languages. It says the 317 same thing in each language. If you can read it in one language, 318 you can ignore the other translations. The other translations may be 319 presented as attachments or grouped together. 321 Este es un mensaje en varios idiomas. Dice lo mismo en 322 cada idioma. Si puede leerlo en un idioma, puede ignorar las otras 323 traducciones. Las otras traducciones pueden presentarse como archivos 324 adjuntos o agrupados. 326 --01189998819991197253 327 Content-Type: message/rfc822 328 Content-Language: en; translation-type=original 329 Content-Disposition: inline 331 Subject: Example of a message in Spanish and English 332 Content-Type: text/plain; charset="US-ASCII" 333 Content-Transfer-Encoding: 7bit 334 MIME-Version: 1.0 336 Hello, this message content is provided in your language. 338 --01189998819991197253 339 Content-Type: message/rfc822 340 Content-Language: es; translation-type=human 341 Content-Disposition: inline 343 Subject: =?UTF-8?Q?Ejemplo_pr=C3=A1ctico_de_mensaje_?= 344 =?UTF-8?Q?en_espa=C3=B1ol_e_ingl=C3=A9s?= 345 Content-Type: text/plain; charset="US-ASCII" 346 Content-Transfer-Encoding: 7bit 347 MIME-Version: 1.0 349 Hola, el contenido de este mensaje esta disponible en su idioma. 351 --01189998819991197253-- 353 8.2. An Example of a Multiple language email message with language 354 independent part 356 Below is an example of a multiple language email message that has the 357 multilingual preface followed by two language message parts and then 358 a language independent png image. 360 From: Nik 361 To: Nathaniel 362 Subject: Example of a message in Spanish and English 363 Date: Thu, 7 Jul 2016 21:08:00 +0100 364 MIME-Version: 1.0 365 Content-Type: multipart/multilingual; 366 boundary="01189998819991197253" 368 --01189998819991197253 369 Content-Type: text/plain; charset="UTF-8" 370 Content-Disposition: inline 371 Content-Transfer-Encoding: quoted-printable 373 This is a message in multiple languages. It says the 374 same thing in each language. If you can read it in one language, 375 you can ignore the other translations. The other translations may be 376 presented as attachments or grouped together. 378 Este es un mensaje en varios idiomas. Dice lo mismo en 379 cada idioma. Si puede leerlo en un idioma, puede ignorar las otras 380 traducciones. Las otras traducciones pueden presentarse como archivos 381 adjuntos o agrupados. 383 --01189998819991197253 384 Content-Type: message/rfc822 385 Content-Language: en; translation-type=original 386 Content-Disposition: inline 388 Subject: Example of a message in Spanish and English 389 Content-Type: text/plain; charset="US-ASCII" 390 Content-Transfer-Encoding: 7bit 391 MIME-Version: 1.0 393 Hello, this message content is provided in your language. 395 --01189998819991197253 396 Content-Type: message/rfc822 397 Content-Language: es; translation-type=human 398 Content-Disposition: inline 400 Subject: =?UTF-8?Q?Ejemplo_pr=C3=A1ctico_de_mensaje_?= 401 =?UTF-8?Q?en_espa=C3=B1ol_e_ingl=C3=A9s?= 402 Content-Type: text/plain; charset="US-ASCII" 403 Content-Transfer-Encoding: 7bit 404 MIME-Version: 1.0 406 Hola, el contenido de este mensaje esta disponible en su idioma. 408 --01189998819991197253 409 Content-Type: message/rfc822; name="Icon" 410 Content-Language: zxx 411 Content-Disposition: inline 413 Content-Type: multipart/mixed; 414 boundary="99911972530118999881"; charset="US-ASCII" 415 Content-Transfer-Encoding: 7bit 416 MIME-Version: 1.0 418 --99911972530118999881 419 Content-Type: image/png; name="icon.png" 420 Content-Disposition: inline 421 Content-Transfer-Encoding: base64 423 iVBORw0KGgoAAAANSUhEUgAAADAAAAAwCAYAAABXAvmHAAAKQ2lDQ1BJQ0MgUHJvZmlsZQAA 424 SA2dlndUU1... shortened for brevity ...7yxfd1SNsEy+OXr76qr 425 997zF2hvZYeDEP5ftGV6Xzx2o9MAAAAASUVORK5CYII= 427 --99911972530118999881-- 428 --01189998819991197253-- 429 8.3. An Example of a complex Multiple language email message with 430 language independent part 432 Below is an example of a more complex multiple language email 433 message. It has the multilingual preface and two language message 434 parts and then a language independent png image. The language 435 message parts have multipart/alternative contents and would therefore 436 require further processing to determine the content to display. 438 From: Nik 439 To: Nathaniel 440 Subject: Example of a message in Spanish and English 441 Date: Thu, 7 Jul 2016 20:55:00 +0100 442 MIME-Version: 1.0 443 Content-Type: multipart/multilingual; 444 boundary="01189998819991197253" 446 --01189998819991197253 447 Content-Type: text/plain; charset="UTF-8" 448 Content-Disposition: inline 449 Content-Transfer-Encoding: quoted-printable 451 This is a message in multiple languages. It says the 452 same thing in each language. If you can read it in one language, 453 you can ignore the other translations. The other translations may be 454 presented as attachments or grouped together. 456 Este es un mensaje en varios idiomas. Dice lo mismo en 457 cada idioma. Si puede leerlo en un idioma, puede ignorar las otras 458 traducciones. Las otras traducciones pueden presentarse como archivos 459 adjuntos o agrupados. 461 --01189998819991197253 462 Content-Type: message/rfc822 463 Content-Language: en; translation-type=original 464 Content-Disposition: inline 466 Subject: Example of a message in Spanish and English 467 Content-Type: multipart/alternative; 468 boundary="72530118999911999881"; charset="US-ASCII" 469 Content-Transfer-Encoding: 7bit 470 MIME-Version: 1.0 472 --72530118999911999881 473 Content-Type: text/plain; charset="US-ASCII" 474 Content-Transfer-Encoding: 7bit 476 Hello, this message content is provided in your language. 478 --72530118999911999881 479 Content-Type: text/html; charset="US-ASCII" 480 Content-Transfer-Encoding: 7bit 482 Hello, this message content is provided in your language. 484 --72530118999911999881-- 485 --01189998819991197253 486 Content-Type: message/rfc822 487 Content-Language: es; translation-type=human 488 Content-Disposition: inline 490 Subject: =?UTF-8?Q?Ejemplo_pr=C3=A1ctico_de_mensaje_?= 491 =?UTF-8?Q?en_espa=C3=B1ol_e_ingl=C3=A9s?= 492 Content-Type: multipart/alternative; 493 boundary="53011899989991197281"; charset="US-ASCII" 494 Content-Transfer-Encoding: 7bit 495 MIME-Version: 1.0 497 --53011899989991197281 498 Content-Type: text/plain; charset="US-ASCII" 499 Content-Transfer-Encoding: 7bit 501 Hola, el contenido de este mensaje esta disponible en su idioma. 503 --53011899989991197281 504 Content-Type: text/html; charset="US-ASCII" 505 Content-Transfer-Encoding: 7bit 507 Hola, el contenido de este mensaje esta 508 disponible en su idioma. 510 --53011899989991197281-- 511 --01189998819991197253 512 Content-Type: message/rfc822; name="Icon" 513 Content-Language: zxx 514 Content-Disposition: inline 516 Content-Type: multipart/mixed; 517 boundary="99911972530118999881"; charset="US-ASCII" 518 Content-Transfer-Encoding: 7bit 519 MIME-Version: 1.0 521 --99911972530118999881 522 Content-Type: image/png; name="icon.png" 523 Content-Disposition: inline 524 Content-Transfer-Encoding: base64 525 iVBORw0KGgoAAAANSUhEUgAAADAAAAAwCAYAAABXAvmHAAAKQ2lDQ1BJQ0MgUHJvZmlsZQAA 526 SA2dlndUU1... shortened for brevity ...7yxfd1SNsEy+OXr76qr 527 997zF2hvZYeDEP5ftGV6Xzx2o9MAAAAASUVORK5CYII= 529 --99911972530118999881-- 530 --01189998819991197253-- 532 9. Changes from Previous Versions 534 9.1. Changes from draft-tomkinson-multilangcontent-01 to draft- 535 tomkinson-slim-multilangcontent-00 537 o File name and version number changed to reflect the proposed WG 538 name SLIM (Selection of Language for Internet Media). 540 o Replaced the Subject-Translation field in the language message 541 parts with Subject and provided US-ASCII and non-US-ASCII 542 examples. 544 o Introduced the language-independent message part. 546 o Many wording improvements and clarifications throughout the 547 document. 549 9.2. Changes from draft-tomkinson-slim-multilangcontent-00 to draft- 550 tomkinson-slim-multilangcontent-01 552 o Added Translation-Type in each language message part to identify 553 the source of the translation (original/human/automated). 555 9.3. Changes from draft-tomkinson-slim-multilangcontent-01 to draft- 556 tomkinson-slim-multilangcontent-02 558 o Changed Translation-Type to be a parameter for the Content- 559 Language field rather than a new separate field. 561 o Added a paragraph about using Content-Disposition field to help 562 non-conforming mail clients correctly render the multilingual 563 preface. 565 o Recommended using a Name parameter on the language part Content- 566 Type to help the recipient identify the translations in non- 567 conforming mail clients. 569 o Many wording improvements and clarifications throughout the 570 document. 572 9.4. Changes from draft-tomkinson-slim-multilangcontent-02 to draft- 573 ietf-slim-multilangcontent-00 575 o Name change to reflect the draft being accepted into SLIM as a 576 working group document. 578 o Updated examples to use UTF-8 encoding where required. 580 o Removed references to 'locale' for identifying language 581 preference. 583 o Recommended language matching schemes from RFC 4647 [RFC4647]. 585 o Renamed the unmatched part to language independent part to 586 reinforce its intended purpose. 588 o Added requirement for using Content-Language: zxx in the language 589 independent part. 591 o Many wording improvements and clarifications throughout the 592 document. 594 9.5. Changes from draft-ietf-slim-multilangcontent-00 to draft-ietf- 595 slim-multilangcontent-01 597 o Changed the inner content type to require message/rfc822 or 598 message/global. 600 o Updated the examples to reflect the new inner content types. 602 o Added to the security considerations to highlight the risk from 603 insufficient spam filters. 605 9.6. Changes from draft-ietf-slim-multilangcontent-01 to draft-ietf- 606 slim-multilangcontent-02 608 o Restricted the use of a From field in the language message parts 609 and the language independent part. 611 o Updated the security considerations to highlight the risk of an 612 unmatched sender addresses that could be set in the language 613 message parts. 615 10. Acknowledgements 617 The authors are grateful for the helpful input received from many 618 people but would especially like to acknowledge the help of Harald 619 Alvestrand, Stephane Bortzmeyer, Eric Burger, Mark Davis, Doug Ewell, 620 Randall Gellens, Gunnar Hellstrom, Sean Leonard, John Levine, Alexey 621 Melnikov, Addison Phillips, Pete Resnick, Fiona Tomkinson, Simon 622 Tyler and Daniel Vargha. 624 The authors would also like to thank Fernando Alvaro and Luis de 625 Pablo for their work on the Spanish translations. 627 11. IANA Considerations 629 The multipart/multilingual MIME type will be registered with IANA. 631 12. Security Considerations 633 Whilst it is intended that each language message part is a direct 634 translation of the original message, this may not always be the case 635 and these parts could contain undesirable content. Therefore there 636 is a possible risk that undesirable text or images could be shown to 637 the recipient if the message is passed through a spam filter that 638 does not check all of the message parts. The risk should be minimal 639 due to the fact that an unknown multipart subtype should be treated 640 as multipart/mixed and so each message part should be subsequently 641 scanned. 643 Because the language message parts have a Content-Type of message/ 644 rfc822 or message/global, they might contain From fields which could 645 have different values to that of the top-level From field and may not 646 reflect the actual sender. An implementation might choose to include 647 a From field, even though it is specified in this document that the 648 language message parts SHOULD NOT have a From field. The incorrect 649 From field values might get shown to the recipient in a non- 650 conforming email client and may mislead the recipient into thinking 651 that the email came from someone other than the real sender. 653 13. References 655 13.1. Normative References 657 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 658 Extensions (MIME) Part Two: Media Types", RFC 2046, 659 DOI 10.17487/RFC2046, November 1996, 660 . 662 [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) 663 Part Three: Message Header Extensions for Non-ASCII Text", 664 RFC 2047, DOI 10.17487/RFC2047, November 1996, 665 . 667 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 668 Requirement Levels", BCP 14, RFC 2119, 669 DOI 10.17487/RFC2119, March 1997, 670 . 672 [RFC2183] Troost, R., Dorner, S., and K. Moore, Ed., "Communicating 673 Presentation Information in Internet Messages: The 674 Content-Disposition Header Field", RFC 2183, 675 DOI 10.17487/RFC2183, August 1997, 676 . 678 [RFC3282] Alvestrand, H., "Content Language Headers", RFC 3282, 679 DOI 10.17487/RFC3282, May 2002, 680 . 682 [RFC4647] Phillips, A. and M. Davis, "Matching of Language Tags", 683 BCP 47, RFC 4647, DOI 10.17487/RFC4647, September 2006, 684 . 686 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 687 Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, 688 September 2009, . 690 13.2. Informational References 692 [I-D.gellens-slim-negotiating-human-language] 693 Gellens, R., "Negotiating Human Language in Real-Time 694 Communications", draft-gellens-slim-negotiating-human- 695 language-02 (work in progress), July 2015. 697 Authors' Addresses 699 Nik Tomkinson 700 Mimecast Ltd 701 CityPoint, One Ropemaker Street 702 London EC2Y 9AW 703 United Kingdom 705 Email: rfc.nik.tomkinson@gmail.com 707 Nathaniel Borenstein 708 Mimecast Ltd 709 480 Pleasant Street 710 Watertown MA 02472 711 North America 713 Email: nsb@mimecast.com