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Reschke 3 Internet-Draft greenbytes 4 Intended status: Standards Track February 21, 2010 5 Expires: August 25, 2010 7 Application of RFC 2231 Encoding to 8 Hypertext Transfer Protocol (HTTP) Header Fields 9 draft-reschke-rfc2231-in-http-10 11 Abstract 13 By default, message header field parameters in Hypertext Transfer 14 Protocol (HTTP) messages can not carry characters outside the ISO- 15 8859-1 character set. RFC 2231 defines an escaping mechanism for use 16 in Multipurpose Internet Mail Extensions (MIME) headers. This 17 document specifies a profile of that encoding suitable for use in 18 HTTP header fields. 20 Editorial Note (To be removed by RFC Editor before publication) 22 There are multiple HTTP header fields that already use RFC 2231 23 encoding in practice (Content-Disposition) or might use it in the 24 future (Link). The purpose of this document is to provide a single 25 place where the generic aspects of RFC 2231 encoding in HTTP header 26 fields are defined. 28 Distribution of this document is unlimited. Although this is not a 29 work item of the HTTPbis Working Group, comments should be sent to 30 the Hypertext Transfer Protocol (HTTP) mailing list at 31 ietf-http-wg@w3.org [1], which may be joined by sending a message 32 with subject "subscribe" to ietf-http-wg-request@w3.org [2]. 34 Discussions of the HTTPbis Working Group are archived at 35 . 37 XML versions, latest edits and the issues list for this document are 38 available from 39 . A 40 collection of test cases is available at 41 . 43 Note: as of January 2010, there were at least three independent 44 implementations of the encoding defined in Section 3.2: Konqueror 45 (trunk), Mozilla Firefox, and Opera. 47 Status of this Memo 48 This Internet-Draft is submitted to IETF in full conformance with the 49 provisions of BCP 78 and BCP 79. 51 Internet-Drafts are working documents of the Internet Engineering 52 Task Force (IETF), its areas, and its working groups. Note that 53 other groups may also distribute working documents as Internet- 54 Drafts. 56 Internet-Drafts are draft documents valid for a maximum of six months 57 and may be updated, replaced, or obsoleted by other documents at any 58 time. It is inappropriate to use Internet-Drafts as reference 59 material or to cite them other than as "work in progress." 61 The list of current Internet-Drafts can be accessed at 62 http://www.ietf.org/ietf/1id-abstracts.txt. 64 The list of Internet-Draft Shadow Directories can be accessed at 65 http://www.ietf.org/shadow.html. 67 This Internet-Draft will expire on August 25, 2010. 69 Copyright Notice 71 Copyright (c) 2010 IETF Trust and the persons identified as the 72 document authors. All rights reserved. 74 This document is subject to BCP 78 and the IETF Trust's Legal 75 Provisions Relating to IETF Documents 76 (http://trustee.ietf.org/license-info) in effect on the date of 77 publication of this document. Please review these documents 78 carefully, as they describe your rights and restrictions with respect 79 to this document. Code Components extracted from this document must 80 include Simplified BSD License text as described in Section 4.e of 81 the Trust Legal Provisions and are provided without warranty as 82 described in the BSD License. 84 Table of Contents 86 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 87 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4 88 3. A Profile of RFC 2231 for Use in HTTP . . . . . . . . . . . . 4 89 3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 5 90 3.2. Parameter Value Character Set and Language Information . . 5 91 3.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 7 92 3.3. Language specification in Encoded Words . . . . . . . . . 8 93 4. Guidelines for Usage in HTTP Header Field Definitions . . . . 8 94 4.1. When to Use the Extension . . . . . . . . . . . . . . . . 9 95 4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . . 9 96 4.3. Using Multiple Instances for Internationalization . . . . 9 97 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 98 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 99 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 100 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 101 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10 102 8.2. Informative References . . . . . . . . . . . . . . . . . . 11 103 Appendix A. Document History and Future Plans (to be removed 104 by RFC Editor before publication) . . . . . . . . . . 12 105 Appendix B. Change Log (to be removed by RFC Editor before 106 publication) . . . . . . . . . . . . . . . . . . . . 12 107 B.1. Since draft-reschke-rfc2231-in-http-00 . . . . . . . . . . 12 108 B.2. Since draft-reschke-rfc2231-in-http-01 . . . . . . . . . . 12 109 B.3. Since draft-reschke-rfc2231-in-http-02 . . . . . . . . . . 13 110 B.4. Since draft-reschke-rfc2231-in-http-03 . . . . . . . . . . 13 111 B.5. Since draft-reschke-rfc2231-in-http-04 . . . . . . . . . . 13 112 B.6. Since draft-reschke-rfc2231-in-http-05 . . . . . . . . . . 13 113 B.7. Since draft-reschke-rfc2231-in-http-06 . . . . . . . . . . 13 114 B.8. Since draft-reschke-rfc2231-in-http-07 . . . . . . . . . . 13 115 B.9. Since draft-reschke-rfc2231-in-http-08 . . . . . . . . . . 13 116 B.10. Since draft-reschke-rfc2231-in-http-09 . . . . . . . . . . 13 117 Appendix C. Resolved issues (to be removed by RFC Editor 118 before publication) . . . . . . . . . . . . . . . . . 13 119 C.1. rfc2978-normative . . . . . . . . . . . . . . . . . . . . 13 120 C.2. rfc3986-normative . . . . . . . . . . . . . . . . . . . . 14 121 C.3. usascii-normative . . . . . . . . . . . . . . . . . . . . 14 122 Appendix D. Open issues (to be removed by RFC Editor prior to 123 publication) . . . . . . . . . . . . . . . . . . . . 14 124 D.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 125 D.2. parameter-abnf . . . . . . . . . . . . . . . . . . . . . . 14 126 D.3. iso8859 . . . . . . . . . . . . . . . . . . . . . . . . . 15 127 D.4. when-ext-value . . . . . . . . . . . . . . . . . . . . . . 15 128 D.5. i18n-spoofing . . . . . . . . . . . . . . . . . . . . . . 15 129 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16 131 1. Introduction 133 By default, message header field parameters in HTTP ([RFC2616]) 134 messages can not carry characters outside the ISO-8859-1 character 135 set ([ISO-8859-1]). RFC 2231 (Appendix of [RFC2231]) defines an 136 escaping mechanism for use in MIME headers. This document specifies 137 a profile of that encoding for use in HTTP header fields. 139 Note: this profile does not apply to message payloads transmitted 140 over HTTP, such as when using the media type "multipart/form-data" 141 ([RFC2388]). 143 2. Notational Conventions 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 uses the ABNF (Augmented Backus-Naur Form) 150 notation defined in [RFC5234]. The following core rules are included 151 by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters), 152 DIGIT (decimal 0-9), HEXDIG (hexadecimal 0-9/A-F/a-f) and LWSP 153 (linear white space). 155 Note that this specification uses the term "character set" for 156 consistency with other IETF specifications such as RFC 2277 (see 157 [RFC2277], Section 3). A more accurate term would be "character 158 encoding" (a mapping of code points to octet sequences). 160 3. A Profile of RFC 2231 for Use in HTTP 162 RFC 2231 defines several extensions to MIME. The sections below 163 discuss if and how they apply to HTTP. 165 In short: 167 o Parameter Continuations aren't needed (Section 3.1), 169 o Character Set and Language Information are useful, therefore a 170 simple subset is specified (Section 3.2), and 172 o Language Specifications in Encoded Words aren't needed 173 (Section 3.3). 175 3.1. Parameter Continuations 177 Section 3 of [RFC2231] defines a mechanism that deals with the length 178 limitations that apply to MIME headers. These limitations do not 179 apply to HTTP ([RFC2616], Section 19.4.7). 181 Thus in HTTP, senders MUST NOT use parameter continuations, and 182 therefore recipients do not need to support them. 184 3.2. Parameter Value Character Set and Language Information 186 Section 4 of [RFC2231] specifies how to embed language information 187 into parameter values, and also how to encode non-ASCII characters, 188 dealing with restrictions both in MIME and HTTP header parameters. 190 However, RFC 2231 does not specify a mandatory-to-implement character 191 set, making it hard for senders to decide which character set to use. 192 Thus, recipients implementing this specification MUST support the 193 character sets "ISO-8859-1" [ISO-8859-1] and "UTF-8" [RFC3629]. 195 Furthermore, RFC 2231 allows leaving out the character set 196 information. The profile defined by this specification does not 197 allow that. 199 The syntax for parameters is defined in Section 3.6 of [RFC2616] 200 (with RFC 2616 implied LWS translated to RFC 5234 LWSP): 202 parameter = attribute LWSP "=" LWSP value 204 attribute = token 205 value = token / quoted-string 207 quoted-string = 208 token = 210 This specification extends the grammar to: 212 parameter = reg-parameter / ext-parameter 214 reg-parameter = attribute LWSP "=" LWSP value 216 ext-parameter = attribute "*" LWSP "=" LWSP ext-value 218 ext-value = charset "'" [ language ] "'" value-chars 219 ; extended-initial-value, 220 ; defined in [RFC2231], Section 7 222 charset = "UTF-8" / "ISO-8859-1" / mime-charset 224 mime-charset = 1*mime-charsetc 225 mime-charsetc = ALPHA / DIGIT 226 / "!" / "#" / "$" / "%" / "&" 227 / "+" / "-" / "^" / "_" / "`" 228 / "{" / "}" / "~" 229 ; as in Section 2.3 of [RFC2978] 230 ; except that the single quote is not included 232 language = 234 value-chars = *( pct-encoded / attr-char ) 236 pct-encoded = "%" HEXDIG HEXDIG 237 ; see [RFC3986], Section 2.1 239 attr-char = ALPHA / DIGIT 240 / "!" / "#" / "$" / "&" / "+" / "-" / "." 241 / "^" / "_" / "`" / "|" / "~" 242 ; token except ( "*" / "'" / "%" ) 244 Thus, a parameter is either regular parameter (reg-parameter), as 245 previously defined in Section 3.6 of [RFC2616], or an extended 246 parameter (ext-parameter). 248 Extended parameters are those where the left hand side of the 249 assignment ends with an asterisk character. 251 The value part of an extended parameter (ext-value) is a token that 252 consists of three parts: the REQUIRED character set name (charset), 253 the OPTIONAL language information (language), and a character 254 sequence representing the actual value (value-chars), separated by 255 single quote characters. Note that both character set names and 256 language tags are restricted to the US-ASCII character set, and are 257 matched case-insensitively (see [RFC2978], Section 2.3 and [RFC5646], 258 Section 2.1.1). 260 Inside the value part, characters not contained in attr-char are 261 encoded into an octet sequence using the specified character set. 262 That octet sequence then is percent-encoded as specified in Section 263 2.1 of [RFC3986]. 265 Producers MUST NOT use character sets other than "UTF-8" ([RFC3629]) 266 or "ISO-8859-1" ([ISO-8859-1]). Extension character sets (ext- 267 charset) are reserved for future use. 269 Note: recipients should be prepared to handle encoding errors, 270 such as malformed or incomplete percent escape sequences, or non- 271 decodable octet sequences, in a robust manner. This specification 272 does not mandate any specific behavior, for instance the following 273 strategies are all acceptable: 275 * ignoring the parameter, 277 * stripping a non-decodable octet sequence, 279 * substituting a non-decodable octet sequence by a replacement 280 character, such as the Unicode character U+FFFD (Replacement 281 Character). 283 Note: the RFC 2616 token production ([RFC2616], Section 2.2) 284 differs from the production used in RFC 2231 (imported from 285 Section 5.1 of [RFC2045]) in that curly braces ("{" and "}") are 286 excluded. Thus, these two characters are excluded from the attr- 287 char production as well. 289 Note: the ABNF defined here differs from the one in 290 Section 2.3 of [RFC2978] in that it does not allow the single 291 quote character (see also RFC Editor Errata ID 1912 [3]). In 292 practice, no character set names using that character have been 293 registered at the time of this writing. 295 3.2.1. Examples 297 Non-extended notation, using "token": 299 foo: bar; title=Economy 301 Non-extended notation, using "quoted-string": 303 foo: bar; title="US-$ rates" 305 Extended notation, using the unicode character U+00A3 (POUND SIGN): 307 foo: bar; title*=iso-8859-1'en'%A3%20rates 309 Note: the Unicode pound sign character U+00A3 was encoded using ISO- 310 8859-1 into the single octet A3, then percent-encoded. Also note 311 that the space character was encoded as %20, as it is not contained 312 in attr-char. 314 Extended notation, using the unicode characters U+00A3 (POUND SIGN) 315 and U+20AC (EURO SIGN): 317 foo: bar; title*=UTF-8''%c2%a3%20and%20%e2%82%ac%20rates 319 Note: the unicode pound sign character U+00A3 was encoded using UTF-8 320 into the octet sequence C2 A3, then percent-encoded. Likewise, the 321 unicode euro sign character U+20AC was encoded into the octet 322 sequence E2 82 AC, then percent-encoded. Also note that HEXDIG 323 allows both lower-case and upper-case character, so recipients must 324 understand both, and that the language information is optional, while 325 the character set is not. 327 3.3. Language specification in Encoded Words 329 Section 5 of [RFC2231] extends the encoding defined in [RFC2047] to 330 also support language specification in encoded words. Although the 331 HTTP/1.1 specification does refer to RFC 2047 ([RFC2616], Section 332 2.2), it's not clear to which header field exactly it applies, and 333 whether it is implemented in practice (see 334 for details). 336 Thus, the RFC 2231 profile defined by this specification does not 337 include this feature. 339 4. Guidelines for Usage in HTTP Header Field Definitions 341 Specifications of HTTP header fields that use the extensions defined 342 in Section 3.2 should clearly state that. A simple way to achieve 343 this is to normatively reference this specification, and to include 344 the ext-value production into the ABNF for that header field. 346 For instance: 348 foo-header = "foo" LWSP ":" LWSP token ";" LWSP title-param 349 title-param = "title" LWSP "=" LWSP value 350 / "title*" LWSP "=" LWSP ext-value 351 ext-value = 353 [[rfcno: Note to RFC Editor: in the figure above, please replace 354 "xxxx" by the RFC number assigned to this specification.]] 356 4.1. When to Use the Extension 358 Section 4.2 of [RFC2277] requires that protocol elements containing 359 text are able to carry language information. Thus, the ext-value 360 production should always be used when the parameter value is of 361 textual nature. 363 Furthermore, the extension should also be used whenever the parameter 364 value needs to carry characters not present in the US-ASCII 365 ([USASCII]) character set (note that it would be unacceptable to 366 define a new parameter that would be restricted to a subset of the 367 Unicode character set). 369 4.2. Error Handling 371 Header specifications that include parameters should also specify 372 whether same-named parameters can occur multiple times. If 373 repetitions are not allowed (and this is believed to be the common 374 case), the specification should state whether regular or the extended 375 syntax takes precedence. In the latter case, this could be used by 376 producers to use both formats without breaking recipients that do not 377 understand the syntax. 379 Example: 381 foo: bar; title="EURO exchange rates"; 382 title*=utf-8''%e2%82%ac%20exchange%20rates 384 In this case, the sender provides an ASCII version of the title for 385 legacy recipients, but also includes an internationalized version for 386 recipients understanding this specification -- the latter obviously 387 should prefer the new syntax over the old one. 389 Note: at the time of this writing, many implementations failed to 390 ignore the form they do not understand, or prioritize the ASCII 391 form although the extended syntax was present. 393 4.3. Using Multiple Instances for Internationalization 395 It is expected that in many cases, internationalization of parameters 396 in response headers is implemented using server driven content 397 negotiation ([RFC2616], Section 12.1) using the Accept-Language 398 header ([RFC2616], Section 14.4). However, the format described in 399 this specification also allows using multiple instances providing 400 multiple languages in a single header. Specifications that want to 401 take advantage of this should clearly specify the expected processing 402 by the recipient. 404 Example: 406 foo: bar; title*=utf-8'en'Document%20Title; 407 title*=utf-8'de'Titel%20des%20Dokuments 409 5. Security Considerations 411 This document does not discuss security issues and is not believed to 412 raise any security issues not already endemic in HTTP. 414 6. IANA Considerations 416 There are no IANA Considerations related to this specification. 418 7. Acknowledgements 420 Thanks to Martin Duerst and Frank Ellermann for help figuring out 421 ABNF details, to Graham Klyne and Alexey Melnikov for general review, 422 and to Benjamin Carlyle and Roar Lauritzsen for implementer's 423 feedback. 425 8. References 427 8.1. Normative References 429 [ISO-8859-1] 430 International Organization for Standardization, 431 "Information technology -- 8-bit single-byte coded graphic 432 character sets -- Part 1: Latin alphabet No. 1", ISO/ 433 IEC 8859-1:1998, 1998. 435 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 436 Requirement Levels", BCP 14, RFC 2119, March 1997. 438 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 439 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 440 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 442 [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration 443 Procedures", BCP 19, RFC 2978, October 2000. 445 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 446 10646", RFC 3629, STD 63, November 2003. 448 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 449 Resource Identifier (URI): Generic Syntax", RFC 3986, 450 STD 66, January 2005. 452 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 453 Specifications: ABNF", STD 68, RFC 5234, January 2008. 455 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying 456 Languages", BCP 47, RFC 5646, September 2009. 458 [USASCII] American National Standards Institute, "Coded Character 459 Set -- 7-bit American Standard Code for Information 460 Interchange", ANSI X3.4, 1986. 462 8.2. Informative References 464 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 465 Extensions (MIME) Part One: Format of Internet Message 466 Bodies", RFC 2045, November 1996. 468 [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) 469 Part Three: Message Header Extensions for Non-ASCII Text", 470 RFC 2047, November 1996. 472 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded 473 Word Extensions: 474 Character Sets, Languages, and Continuations", RFC 2231, 475 November 1997. 477 [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and 478 Languages", BCP 18, RFC 2277, January 1998. 480 [RFC2388] Masinter, L., "Returning Values from Forms: multipart/ 481 form-data", RFC 2388, August 1998. 483 URIs 485 [1] 487 [2] 489 [3] 491 Appendix A. Document History and Future Plans (to be removed by RFC 492 Editor before publication) 494 Problems with the internationalization of the HTTP Content- 495 Disposition header field have been known for many years (see test 496 cases at ). 498 During IETF 72 499 (), the 500 HTTPbis Working Group shortly discussed how to deal with the 501 underspecification of (1) Content-Disposition, and its (2) 502 internationalization aspects. Back then, there was rough consensus 503 in the room to move the definition into a separate draft. 505 This specification addresses problem (2), by defining a simple subset 506 of the encoding format defined in RFC 2231. A separate 507 specification, draft-reschke-rfc2183-in-http, is planned to address 508 problem (1). Note that this approach was chosen because Content- 509 Disposition is just an example for an HTTP header field using this 510 kind of encoding. Another example is the currently proposed Link 511 header field (draft-nottingham-http-link-header). 513 This document is planned to be published on the IETF Standards Track, 514 so that other standards-track level documents can depend on it, such 515 as the new specification of Content-Disposition, or potentially 516 future revisions of the HTTP Link Header specification. 518 Also note that this document specifies a proper subset of the 519 extensions defined in RFC 2231, but does not normatively refer to it. 520 Thus, RFC 2231 can be revised separately, should the email community 521 decide to. 523 Appendix B. Change Log (to be removed by RFC Editor before publication) 525 B.1. Since draft-reschke-rfc2231-in-http-00 527 Use RFC5234-style ABNF, closer to the one used in RFC 2231. 529 Make RFC 2231 dependency informative, so this specification can 530 evolve independently. 532 Explain the ABNF in prose. 534 B.2. Since draft-reschke-rfc2231-in-http-01 536 Remove unneeded RFC5137 notation (code point vs character). 538 B.3. Since draft-reschke-rfc2231-in-http-02 540 And and resolve issues "charset", "repeats" and "rfc4646". 542 B.4. Since draft-reschke-rfc2231-in-http-03 544 And and resolve issue "charsetmatch". 546 B.5. Since draft-reschke-rfc2231-in-http-04 548 Add and resolve issues "badseq" and "tokenquotcharset". 550 B.6. Since draft-reschke-rfc2231-in-http-05 552 Say "header field" instead of "header" in the context of HTTP. 554 B.7. Since draft-reschke-rfc2231-in-http-06 556 Add an appendix discussing document history and future plans, to be 557 removed before publication. 559 B.8. Since draft-reschke-rfc2231-in-http-07 561 Add and resolve issues "impl" and "rel-2388". 563 B.9. Since draft-reschke-rfc2231-in-http-08 565 Editorial improvements. Add and resolve issues "attrcharvstoken" and 566 "tokengrammar". 568 B.10. Since draft-reschke-rfc2231-in-http-09 570 Add issues "i18n-spoofing", "iso8859", "parameter-abnf", and "when- 571 ext-value". Add and resolve issues "rfc2978-normative", "rfc3986- 572 normative" and "usascii-normative". 574 Appendix C. Resolved issues (to be removed by RFC Editor before 575 publication) 577 Issues that were either rejected or resolved in this version of this 578 document. 580 C.1. rfc2978-normative 582 In Section 3.2: 584 Type: change 585 julian.reschke@greenbytes.de (2010-02-20): The reference to RFC2978 586 needs to be normative (reported by Alexey Melnikov). 588 Resolution (2010-02-20): Done. 590 C.2. rfc3986-normative 592 In Section 3.2: 594 Type: change 596 julian.reschke@greenbytes.de (2010-02-20): The reference to percent- 597 encoding (RFC3986) needs to be normative (reported by Alexey 598 Melnikov). 600 Resolution (2010-02-20): Done. 602 C.3. usascii-normative 604 In Section 4.1: 606 Type: change 608 julian.reschke@greenbytes.de (2010-02-20): The reference to USASCII 609 needs to be normative. 611 Resolution (2010-02-20): Done. 613 Appendix D. Open issues (to be removed by RFC Editor prior to 614 publication) 616 D.1. edit 618 Type: edit 620 julian.reschke@greenbytes.de (2009-04-17): Umbrella issue for 621 editorial fixes/enhancements. 623 D.2. parameter-abnf 625 In Section 3.2: 627 Type: change 629 julian.reschke@greenbytes.de (2010-02-20): The ABNF for reg-parameter 630 and ext-parameter is ambiguous, as "*" is a valid token character; 631 furthermore, RFC 2616's "attribute" production allows "*" while RFC 632 2231's does not. (reported by Alexey Melnikov). 634 julian.reschke@greenbytes.de (2010-02-21): Proposal: destrict the 635 allowable character set in parameter names to exclude "*" (amd maybe 636 even more non-name characters?). Also, consider extending the set of 637 value characters (for the right hand side) to allow more characters 638 that can be umabigouously parsed outside quoted strings, such as "/". 640 D.3. iso8859 642 In Section 3.2: 644 Type: change 646 julian.reschke@greenbytes.de (2010-02-20): The protocol could be 647 further simplified by mandating UTF-8 only (reported by Alexey 648 Melnikov). On the other hand and not surprinsingly, testing shows 649 that ISO-8859-1 support is widely implemented. The author is looking 650 for community feedback on this choice. 652 D.4. when-ext-value 654 In Section 4.1: 656 Type: change 658 julian.reschke@greenbytes.de (2010-02-18): There's no point in using 659 ext-value when the language is unknown and no "special" characters 660 are present. 662 D.5. i18n-spoofing 664 In Section 5: 666 Type: change 668 671 GK@ninebynine.org (2010-02-20): I note that the security 672 considerations section says nothing about possible character 673 "spoofing" - i.e. making a displayed prompt or value appear to be 674 something other than it is. E.g. Non-ASCII characters have been 675 used to set up exploits involving dodgy URIs that may appear to a 676 user to be legitimate. 678 Author's Address 680 Julian F. Reschke 681 greenbytes GmbH 682 Hafenweg 16 683 Muenster, NW 48155 684 Germany 686 Email: julian.reschke@greenbytes.de 687 URI: http://greenbytes.de/tech/webdav/