MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)
RFC 2557

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Network Working Group                                         J. Palme
Request for Comments: 2557                    Stockholm University/KTH
Obsoletes: 2110                                             A. Hopmann
Category: Standards Track                        Microsoft Corporation
                                                           N. Shelness
                                         Lotus Development Corporation
                                                            March 1999

    MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

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

Abstract

   HTML [RFC 1866] defines a powerful means of specifying multimedia
   documents. These multimedia documents consist of a text/html root
   resource (object) and other subsidiary resources (image, video clip,
   applet, etc. objects) referenced by Uniform Resource Identifiers
   (URIs) within the text/html root resource. When an HTML multimedia
   document is retrieved by a browser, each of these component resources
   is individually retrieved in real time from a location, and using a
   protocol, specified by each URI.

   In order to transfer a complete HTML multimedia document in a single
   e-mail message, it is necessary to: a) aggregate a text/html root
   resource and all of the subsidiary resources it references into a
   single composite message structure, and b) define a means by which
   URIs in the text/html root can reference subsidiary resources within
   that composite message structure.

   This document a) defines the use of a MIME multipart/related
   structure to aggregate a text/html root resource and the subsidiary
   resources it references, and b) specifies a MIME content-header
   (Content-Location) that allow URIs in a multipart/related text/html
   root body part to reference subsidiary resources in other body parts
   of the same multipart/related structure.

Palme, et al.               Standards Track                     [Page 1]
RFC 2557       MIME Encapsulation of Aggregate Documents      March 1999

   While initially designed to support e-mail transfer of complete
   multi-resource HTML multimedia documents, these conventions can also
   be employed to resources retrieved by other transfer protocols such
   as HTTP and FTP to retrieve a complete multi-resource HTML multimedia
   document in a single transfer or for storage and archiving of
   complete HTML-documents.

   Differences between this and a previous version of this standard,
   which was published as RFC 2110, are summarized in chapter 12.

Table of Contents

   1. Introduction .................................................   3
   2. Terminology  .................................................   4
      2.1 Conformance requirement terminology ......................   4
      2.2 Other terminology ........................................   4
   3. Overview .....................................................   6
   4. The Content-Location MIME Content Header .....................   6
      4.1 MIME content headers .....................................   6
      4.2 The Content-Location Header ..............................   7
      4.3 URIs of MHTML aggregates .................................   8
      4.4 Encoding and decoding of URIs in MIME header fields ......   8
   5. Base URIs for resolution of relative URIs ....................   9
   6. Sending documents without linked objects .....................  10
   7. Use of the Content-Type "multipart/related" ..................  11
   8. Usage of Links to Other Body Parts ...........................  13
      8.1 General principle ........................................  13
      8.2 Resolution of URIs in text/html body parts ...............  13
      8.3 Use of the Content-ID header and CID URLs ................  14
   9. Examples .....................................................  14
      9.1 Example of a HTML body without included linked objects ...  15
      9.2 Example with an absolute URI to an embedded GIF picture ..  15
      9.3 Example with relative URIs to embedded GIF pictures ......  16
      9.4 Example with a relative URI and no BASE available ........  17
      9.5 Example using CID URL and Content-ID header to an embedded
          GIF picture ..............................................  18
      9.6 Example showing permitted and forbidden references between
          nested body parts ........................................  19
   10. Character encoding issues and end-of-line issues ............  21