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Versions: 00 01 02 RFC 2854

Internet-Draft                                               D. Connolly
                                         World Wide Web Consortium (W3C)
Category: Informational                                      L. Masinter
                                                       Xerox Corporation
draft-connolly-text-html-01.txt                         October 13, 1999
Obsoletes: RFC 1866, RFC 2070, RFC 1980, RFC 1867, RFC 1942

                      The 'text/html' Media Type

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet-Drafts
   as reference material or to cite them other than as ``work in
   progress''.

   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
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Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

   This document summarizes the history of HTML development, and
   defines the "text/html" MIME type by pointing to the relevant W3C
   recommendations; it is intended to obsolete the previous IETF
   documents defining HTML, including RFC 1866, RFC 1867, RFC 1980,
   RFC 1942 and RFC 2070, and to remove HTML from IETF Standards
   Track.

   This document was prepared at the request of the W3C HTML working
   group. Please send comments to www-html@w3.org, a public mailing
   list with archive at
   <http://lists.w3.org/Archives/Public/www-html/>.

1. Introduction and background

   HTML has been in use in the World Wide Web information
   infrastructure since 1990, and specified in various informal
   documents.  The text/html media type was first officially defined
   by the IETF HTML working group in 1995 in [HTML20]. Extensions to
   HTML were proposed in [HTML30], [UPLOAD], [TABLES], [CLIMAPS], and
   [I18N].

   The HTML working group closed Sep 1996, and work on defining HTML
   moved to the World Wide Web Consortium (W3C). The proposed
   extensions were incorporated to some extent in [HTML32], and to a
   larger extent in [HTML40]. The definition of multipart/form-data
   from [UPLOAD] was described in [FORMDATA]. In addition, a
   reformulation of HTML 4.0 in XML 1.0 is being developed [XHTML1].

   [HTML32] notes "This specification defines HTML version 3.2. HTML
   3.2 aims to capture recommended practice as of early '96 and as
   such to be used as a replacement for HTML 2.0 (RFC 1866)."
   Subsequent specifications for HTML describe the differences in each
   version.

   In addition to the development of standards, a wide variety of
   additional extensions, restrictions, and modifications to HTML were
   popularized by NCSA's Mosaic system and subsequently by the
   competitive implementations of Netscape Navigator and Microsoft
   Internet Explorer; these extensions are documented in numerous
   books and online guides.

2. Registration of MIME media type text/html

   MIME media type name:      text
   MIME subtype name:         html
   Required parameters:       none
   Optional parameters:

     charset
       The optional parameter "charset" refers to the character
       encoding used to represent the HTML document as a sequence of
       bytes. Any registered IANA charset may be used, but UTF-8 is
       preferred.  Although this parameter is optional, it is strongly
       recommended that it always be present. See Section 6 below
       for a discussion of charset default rules.

     Note that [HTML20] included an optional "level" parameter; in
     practice, this parameter was never used and has been removed from
     this specification.  [HTML30] also suggested a "version"
     parameter; in practice, this parameter also was never used and
     has been removed from this specification.

  Encoding considerations:
     See Section 4 of this document.

  Security considerations:
     See Section 7 of this document.

  Interoperability considerations:
     HTML is designed to be interoperable across the widest possible
     range of platforms and devices of varying capabilities.  However,
     there are contexts (platforms of limited display capability, for
     example) where not all of the capabilities of the full HTML
     definition are feasible. There is ongoing work to develop both a
     modularization of HTML and a set of profiling capabilities to
     identify and negotiate restricted (and extended) capabilities.

     Due to the long and distributed development of HTML, current
     practice on the Internet includes a wide variety of HTML
     variants. Implementors of text/html interpreters must be prepared
     to be "bug-compatible" with popular browsers in order to work
     with many HTML documents available the Internet.

     Typically, different versions are distinguishable by the DOCTYPE
     declaration contained within them, although the DOCTYPE
     declaration itself is sometimes omitted or incorrect.

  Published specification:
     The text/html media type is now defined by W3C Recommendations;
     the latest published version is [HTML40]. As of this writing, a
     revision, HTML 4.01 [HTML401], is being developed as a revision.
     In addition, [XHTML1], also a work in progress, defines a profile
     of use of XHTML which is compatible with HTML 4.0 and which may
     also be labeled as text/html.

  Applications which use this media type:
     The first and most common application of HTML is the World Wide
     Web; commonly, HTML documents contain URI references [URI] to
     other documents and media to be retrieved using the HTTP protocol
     [HTTP]. Many gateway applications provide HTML-based interfaces
     to other underlying complex services. Numerous other applications
     now also use HTML as a convenient platform-independent multimedia
     document representation.

  Additional information:

     Magic number:
       There is no single initial string that is always present for
       HTML files. However, Section 5 below gives some guidelines
       for recognizing HTML files.

     File extension:
       The file extensions 'html' or 'htm' are commonly used, but
       other extensions denoting file formats for preprocessing are
       also common.

     Macintosh File Type code: HTML

   Person & email address to contact for further information:
     Dan Connolly <connolly@w3.org>
     Larry Masinter <masinter@parc.xerox.com>

   Intended usage: COMMON

   Author/Change controller:
     The HTML specification is a work product of the World Wide Web
     Consortium's HTML Working Group.  The W3C has change control over
     the HTML specification.

   Further information:
     HTML has a means of including, by reference via URI, additional
     resources (image, video clip, applet) within the base
     document. In order to transfer a complete HTML object and the
     included resources in a single MIME object, the mechanisms of
     [MHTML] may be used.

3. Fragment Identifiers

   The URI specification [URI] notes that the semantics of a fragment
   identifier (part of a URI after a "#") is a property of the data
   resulting from a retrieval action, and that the format and
   interpretation of fragment identifiers is dependent on the media
   type of the retrieval result.

   For documents labeled as text/html, the fragment identifier
   designates the correspondingly named A element (named with a "name"
   attribute), or any other element (named with the an "id"
   attribute); this is described in detail in [HTML40] section 12.

4. Encoding considerations

   Because of the availability within HTML itself for using character
   entity references for non-ASCII characters, it is possible that
   text/html documents with a wide repertoire of characters may be
   transported without encoding. However, transport of text/html using
   a charset other than US-ASCII may require base64 or
   quoted-printable encoding for 7-bit channels.

   The canonical form of any MIME "text" subtype MUST always represent
   a line break as a CRLF sequence.  Similarly, any occurrence of CRLF
   in MIME "text" MUST represent a line break.  Use of CR and LF
   outside of line break sequences is also forbidden.  This rule
   applies regardless of format or character set or sets involved.

   Note, however, that HTTP allows the transport of data not in
   canonical form, and, in particular, with other end-of-line
   conventions; see [HTTP] section 3.7.1. This exception is commonly
   used for HTML.

   HTML sent via email is still subject to the MIME restrictions; this
   is discussed fully in [MHTML] Section 10.

5. Recognizing HTML files

   Almost all HTML files have the string "<html" or "<HTML" near the
   beginning of the file.

   Documents conformant to HTML 2.0, HTML 3.2 and HTML 4.0 will start
   with a DOCTYPE declaration "<!DOCTYPE HTML" near the beginning,
   before the "<html". These dialects are case insensitive.  Files may
   start with white space, comments (introduced by "<!--" ), or
   processing instructions (introduced by "<?") prior to the DOCTYPE
   declaration.

   XHTML documents (optionally) start with an XML declaration which
   begins with "<?xml" and are required to have a DOCTYPE declaration
   "<!DOCTYPE html".

6. Charset default rules

   The use of an explicit charset parameter is strongly recommended.
   While [MIME] specifies "The default character set, which must be
   assumed in the absence of a charset parameter, is US-ASCII."
   [HTTP] Section 3.7.1, defines that "media subtypes of the 'text'
   type are defined to have a default charset value of 'ISO-8859-1'".
   Section 19.3 of [HTTP] gives additional guidelines.  Using an
   explicit charset parameter will help avoid confusion.

7. Security Considerations

   [HTML40], section B.10, notes various security issues with
   interpreting anchors and forms in HTML documents.

   In addition, the introduction of scripting languages and
   interactive capabilities in HTML 4.0 introduced a number of
   security risks associated with the automatic execution of programs
   written by the sender but interpreted by the recipient.  User
   agents executing such scripts or programs must be extremely careful
   to insure that untrusted software is executed in a protected
   environment.

8. Author's Address

   Daniel W. Connolly
   World Wide Web Consortium (W3C)
   MIT Laboratory for Computer Science
   545 Technology Square
   Cambridge, MA 02139, U.S.A.
   phone:+1-512-310-2971
   mailto:connolly@w3.org
   http://www.w3.org/People/Connolly/

   Larry Masinter
   Palo Alto Research Center
   Xerox Corporation
   3333 Coyote Hill Road
   Palo Alto, CA 94304
   mailto: masinter@parc.xerox.com
   http://purl.org/NET/masinter

9. References

[HTML30] "HyperText Markup Language Specification Version 3.0." Dave
         Raggett, September 1995. Internet Draft (expired). Available
         at <http://www.w3.org/MarkUp/html3/CoverPage>.

[HTML20] "Hypertext Markup Language - 2.0." T. Berners-Lee &
         D. Connolly. RFC 1866. November 1995. Additional information
         available at <http://www.w3.org/MarkUp/html-spec/>.

[UPLOAD] "Form-based File Upload in HTML." E. Nebel & L. Masinter. RFC
         1867. November 1995.

[TABLES] "HTML Tables." D. Raggett. RFC 1942. May 1996.

[CLIMAPS] "A Proposed Extension to HTML : Client-Side Image Maps."
         J. Seidman. RFC 1980. August 1996.

[MIME]   "Multipurpose Internet Mail Extensions (MIME) Part Two: Media
         Types." N. Freed & N. Borenstein. November 1996. RFC 2046.

[HTML32] "HTML 3.2 Reference Specification." Dave Raggett. W3C
         Recomendation. 14 January 1997. Available at
         <http://www.w3.org/TR/REC-html32>.

[I18N] "Internationalization of the Hypertext Markup Language."  RFC
         2070. F. Yergeau, G. Nicol, G. Adams, M. Duerst. January
         1997.

[FORMDATA] "Returning Values from Forms: multipart/form-data".  RFC
         2388. L. Masinter. August 1998.

[HTML40] "HTML 4.0 Specification." Raggett, Le Hors, Jacobs. W3C
         Recommendation. 18 Dec 1997. Available at
         <http://www.w3.org/TR/REC-html40>.

[HTML401] "HTML 4.01 Specification." D. Raggett, A. Le Hors,
         I. Jacobs.  W3C Proposed Recommendation (work in progress),
         August 1999. Available at
         <http://www.w3.org/TR/1999/PR-html40-19990824>.

[XHTML1] "XHTML 1.0: The Extensible HyperText Markup Language: A
         Reformulation of HTML 4.0 in XML 1.0." W3C HTML Working
         Group. W3C Proposed Recommendation (work in progress). August
         1999. Available at <http://www.w3.org/TR/xhtml1>.

[MHTML]  "MIME Encapsulation of Aggregate Documents, such as
         HTML (MHTML)". J. Palme, A. Hopmann, N. Shelness.
         March 1999. RFC 2557.

[URI]    "Uniform Resource Identifiers (URI): Generic Syntax."
         T. Berners-Lee, R. Fielding, L. Masinter. August 1998,
         RFC 2396.

[HTTP]   "Hypertext Transfer Protocol -- HTTP/1.1." R. Fielding,
         J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach,
         T. Berners-Lee. June 1999.RFC 2616.


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