path: root/doc/rfc/rfc1896.txt

Network Working Group                                         P. Resnick
Request for Comments: 1896                                      QUALCOMM
Obsoletes: 1523, 1563                                          A. Walker
Category: Informational                                         InterCon
                                                           February 1996


                  The text/enriched MIME Content-type

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   MIME [RFC-1521] defines a format and general framework for the
   representation of a wide variety of data types in Internet mail. This
   document defines one particular type of MIME data, the text/enriched
   MIME type. The text/enriched MIME type is intended to facilitate the
   wider interoperation of simple enriched text across a wide variety of
   hardware and software platforms. This document is only a minor
   revision to the text/enriched MIME type that was first described in
   [RFC-1523] and [RFC-1563], and is only intended to be used in the
   short term until other MIME types for text formatting in Internet
   mail are developed and deployed.

The text/enriched MIME type

   In order to promote the wider interoperability of simple formatted
   text, this document defines an extremely simple subtype of the MIME
   content-type "text", the "text/enriched" subtype. The content-type
   line for this type may have one optional parameter, the "charset"
   parameter, with the same values permitted for the "text/plain" MIME
   content-type.

   The text/enriched subtype was designed to meet the following
   criteria:

   1. The syntax must be extremely simple to parse, so that even
      teletype-oriented mail systems can easily strip away the
      formatting information and leave only the readable text.

   2. The syntax must be extensible to allow for new formatting
      commands that are deemed essential for some application.





Resnick & Walker             Informational                      [Page 1]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


   3. If the character set in use is ASCII or an 8-bit ASCII superset,
      then the raw form of the data must be readable enough to be
      largely unobjectionable in the event that it is displayed on the
      screen of the user of a non-MIME-conformant mail reader.

   4. The capabilities must be extremely limited, to ensure that it can
      represent no more than is likely to be representable by the
      user's primary word processor. While this limits what can be
      sent, it increases the likelihood that what is sent can be
      properly displayed.

   There are other text formatting standards which meet some of these
   criteria. In particular, HTML and SGML have come into widespread use
   on the Internet. However, there are two important reasons that this
   document further promotes the use of text/enriched in Internet mail
   over other such standards:

   1. Most MIME-aware Internet mail applications are already able to
      either properly format text/enriched mail or, at the very least,
      are able to strip out the formatting commands and display the
      readable text. The same is not true for HTML or SGML.

   2. The current RFC on HTML [RFC-1866] and Internet Drafts on SGML
      have many features which are not necessary for Internet mail, and
      are missing a few capabilities that text/enriched already has.

   For these reasons, this document is promoting the use of
   text/enriched until other Internet standards come into more
   widespread use. For those who will want to use HTML, Appendix B of
   this document contains a very simple C program that converts
   text/enriched to HTML 2.0 described in [RFC-1866].

Syntax

   The syntax of "text/enriched" is very simple. It represents text in a
   single character set--US-ASCII by default, although a different
   character set can be specified by the use of the "charset" parameter.
   (The semantics of text/enriched in non-ASCII character sets are
   discussed later in this document.) All characters represent
   themselves, with the exception of the "<" character (ASCII 60), which
   is used to mark the beginning of a formatting command. A literal
   less-than sign ("<") can be represented by a sequence of two such
   characters, "<<".

   Formatting instructions consist of formatting commands surrounded by
   angle brackets ("<>", ASCII 60 and 62). Each formatting command may
   be no more than 60 characters in length, all in US-ASCII, restricted
   to the alphanumeric and hyphen ("-") characters. Formatting commands



Resnick & Walker             Informational                      [Page 2]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


   may be preceded by a solidus ("/", ASCII 47), making them negations,
   and such negations must always exist to balance the initial opening
   commands.  Thus, if the formatting command "<bold>" appears at some
   point, there must later be a "</bold>" to balance it. (NOTE: The 60
   character limit on formatting commands does NOT include the "<", ">",
   or "/" characters that might be attached to such commands.)
   Formatting commands are always case-insensitive. That is, "bold" and
   "BoLd" are equivalent in effect, if not in good taste.

Line break rules

   Line breaks (CRLF pairs in standard network representation) are
   handled specially. In particular, isolated CRLF pairs are translated
   into a single SPACE character. Sequences of N consecutive CRLF pairs,
   however, are translated into N-1 actual line breaks. This permits
   long lines of data to be represented in a natural looking manner
   despite the frequency of line-wrapping in Internet mailers. When
   preparing the data for mail transport, isolated line breaks should be
   inserted wherever necessary to keep each line shorter than 80
   characters. When preparing such data for presentation to the user,
   isolated line breaks should be replaced by a single SPACE character,
   and N consecutive CRLF pairs should be presented to the user as N-1
   line breaks.

   Thus text/enriched data that looks like this:

     This is
     a single
     line

     This is the
     next line.


     This is the
     next section.

   should be displayed by a text/enriched interpreter as follows:

     This is a single line
     This is the next line.

     This is the next section.

   The formatting commands, not all of which will be implemented by all
   implementations, are described in the following sections.





Resnick & Walker             Informational                      [Page 3]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


Formatting Commands

   The text/enriched formatting commands all begin with <commandname>
   and end with </commandname>, affecting the formatting of the text
   between those two tokens. The commands are described here, grouped
   according to type.

Parameter Command

   Some of the formatting commands may require one or more associated
   parameters. The "param" command is a special formatting command used
   to include these parameters.

     Param
          Marks the affected text as command parameters, to be
          interpreted or ignored by the text/enriched interpreter,
          but not to be shown to the reader. The "param" command
          always immediately follows some other formatting command,
          and the parameter data indicates some additional
          information about the formatting that is to be done. The
          syntax of the parameter data (whatever appears between
          the initial "<param>" and the terminating "</param>") is
          defined for each command that uses it. However, it is
          always required that the format of such data must not
          contain nested "param" commands, and either must not use
          the "<" character or must use it in a way that is
          compatible with text/enriched parsing. That is, the end
          of the parameter data should be recognizable with either
          of two algorithms: simply searching for the first
          occurrence of "</param>" or parsing until a balanced
          "</param>" command is found. In either case, however, the
          parameter data should not be shown to the human reader.

Font-Alteration Commands

   The following formatting commands are intended to alter the font in
   which text is displayed, but not to alter the indentation or
   justification state of the text:

     Bold
          causes the affected text to be in a bold font. Nested
          bold commands have the same effect as a single bold
          command.

     Italic
          causes the affected text to be in an italic font. Nested
          italic commands have the same effect as a single italic
          command.



Resnick & Walker             Informational                      [Page 4]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


     Underline
          causes the affected text to be underlined. Nested
          underline commands have the same effect as a single
          underline command.

     Fixed
          causes the affected text to be in a fixed width font.
          Nested fixed commands have the same effect as a single
          fixed command.

     FontFamily
          causes the affected text to be displayed in a specified
          typeface. The "fontfamily" command requires a parameter
          that is specified by using the "param" command. The
          parameter data is a case-insensitive string containing
          the name of a font family. Any currently available font
          family name (e.g. Times, Palatino, Courier, etc.) may be
          used. This includes font families defined by commercial
          type foundries such as Adobe, BitStream, or any other
          such foundry. Note that implementations should only use
          the general font family name, not the specific font name
          (e.g. use "Times", not "TimesRoman" nor
          "TimesBoldItalic"). When nested, the inner "fontfamily"
          command takes precedence. Also note that the "fontfamily"
          command is advisory only; it should not be expected that
          other implementations will honor the typeface information
          in this command since the font capabilities of systems
          vary drastically.

     Color
          causes the affected text to be displayed in a specified
          color. The "color" command requires a parameter that is
          specified by using the "param" command. The parameter
          data can be one of the following:

               red
               blue
               green
               yellow
               cyan
               magenta
               black
               white

          or an RGB color value in the form:

               ####,####,####




Resnick & Walker             Informational                      [Page 5]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


          where '#' is a hexadecimal digit '0' through '9', 'A'
          through 'F', or 'a' through 'f'. The three 4-digit
          hexadecimal values are the RGB values for red, green, and
          blue respectively, where each component is expressed as
          an unsigned value between 0 (0000) and 65535 (FFFF). The
          default color for the message is unspecified, though
          black is a common choice in many environments. When
          nested, the inner "color" command takes precedence.

     Smaller
          causes the affected text to be in a smaller font. It is
          recommended that the font size be changed by two points,
          but other amounts may be more appropriate in some
          environments. Nested smaller commands produce ever
          smaller fonts, to the limits of the implementation's
          capacity to reasonably display them, after which further
          smaller commands have no incremental effect.

     Bigger
          causes the affected text to be in a bigger font. It is
          recommended that the font size be changed by two points,
          but other amounts may be more appropriate in some
          environments. Nested bigger commands produce ever bigger
          fonts, to the limits of the implementation's capacity to
          reasonably display them, after which further bigger
          commands have no incremental effect.

   While the "bigger" and "smaller" operators are effectively inverses,
   it is not recommended, for example, that "<smaller>" be used to end
   the effect of "<bigger>". This is properly done with "</bigger>".

   Since the capabilities of implementations will vary, it is to be
   expected that some implementations will not be able to act on some of
   the font-alteration commands. However, an implementation should still
   display the text to the user in a reasonable fashion. In particular,
   the lack of capability to display a particular font family, color, or
   other text attribute does not mean that an implementation should fail
   to display text.

Fill/Justification/Indentation Commands

   Initially, text/enriched text is intended to be displayed fully
   filled (that is, using the rules specified for replacing CRLF pairs
   with spaces or removing them as appropriate) with appropriate kerning
   and letter-tracking, and using the maximum available margins as suits
   the capabilities of the receiving user agent software.





Resnick & Walker             Informational                      [Page 6]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


   The following commands alter that state. Each of these commands force
   a line break before and after the formatting environment if there is
   not otherwise a line break. For example, if one of these commands
   occurs anywhere other than the beginning of a line of text as
   presented, a new line is begun.

     Center
          causes the affected text to be centered.

     FlushLeft
          causes the affected text to be left-justified with a
          ragged right margin.

     FlushRight
          causes the affected text to be right-justified with a
          ragged left margin.

     FlushBoth
          causes the affected text to be filled and padded so as to
          create smooth left and right margins, i.e., to be fully
          justified.

     ParaIndent
          causes the running margins of the affected text to be
          moved in. The recommended indentation change is the width
          of four characters, but this may differ among
          implementations. The "paraindent" command requires a
          parameter that is specified by using the "param" command.
          The parameter data is a comma-seperated list of one or
          more of the following:

          Left
               causes the running left margin to be moved to the
               right.

          Right
               causes the running right margin to be moved to the
               left.

          In
               causes the first line of the affected paragraph to
               be indented in addition to the running margin. The
               remaining lines remain flush to the running margin.

          Out
               causes all lines except for the first line of the
               affected paragraph to be indented in addition to the
               running margin. The first line remains flush to the



Resnick & Walker             Informational                      [Page 7]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


               running margin.

     Nofill
          causes the affected text to be displayed without filling.
          That is, the text is displayed without using the rules
          for replacing CRLF pairs with spaces or removing
          consecutive sequences of CRLF pairs. However, the current
          state of the margins and justification is honored; any
          indentation or justification commands are still applied
          to the text within the scope of the "nofill".

   The "center", "flushleft", "flushright", and "flushboth" commands are
   mutually exclusive, and, when nested, the inner command takes
   precedence.

   The "nofill" command is mutually exclusive with the "in" and "out"
   parameters of the "paraindent" command; when they occur in the same
   scope, their behavior is undefined.

   The parameter data for the "paraindent" command may contain multiple
   occurances of the same parameter (i.e. "left", "right", "in", or
   "out").  Each occurance causes the text to be further indented in the
   manner indicated by that parameter. Nested "paraindent" commands
   cause the affected text to be further indented according to the
   parameters. Note that the "in" and "out" parameters for "paraindent"
   are mutually exclusive; when they appear together or when nested
   "paraindent" commands contain both of them, their behavior is
   undefined.

   For purposes of the "in" and "out" parameters, a paragraph is defined
   as text that is delimited by line breaks after applying the rules for
   replacing CRLF pairs with spaces or removing consecutive sequences of
   CRLF pairs. For example, within the scope of an "out", the line
   following each CRLF is made flush with the running margin, and
   subsequent lines are indented. Within the scope of an "in", the first
   line following each CRLF is indented, and subsequent lines remain
   flush to the running margin.

   Whether or not text is justified by default (that is, whether the
   default environment is "flushleft", "flushright", or "flushboth") is
   unspecified, and depends on the preferences of the user, the
   capabilities of the local software and hardware, and the nature of
   the character set in use. On systems where full justification is
   considered undesirable, the "flushboth" environment may be identical
   to the default environment. Note that full justification should never
   be performed inside of "center", "flushleft", "flushright", or
   "nofill" environments.  Note also that for some non-ASCII character
   sets, full justification may be fundamentally inappropriate.



Resnick & Walker             Informational                      [Page 8]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


   Note that [RFC-1563] defined two additional indentation commands,
   "Indent" and "IndentRight". These commands did not force a line
   break, and therefore their behavior was unpredictable since they
   depended on the margins and character sizes that a particular
   implementation used.  Therefore, their use is deprecated and they
   should be ignored just as other unrecognized commands.

Markup Commands

   Commands in this section, unlike the other text/enriched commands are
   declarative markup commands. Text/enriched is not intended as a full
   markup language, but instead as a simple way to represent common
   formatting commands. Therefore, markup commands are purposely kept to
   a minimum. It is only because each was deemed so prevalent or
   necessary in an e-mail environment that these particular commands
   have been included at all.

     Excerpt
          causes the affected text to be interpreted as a textual
          excerpt from another source, probably a message being
          responded to. Typically this will be displayed using
          indentation and an alternate font, or by indenting lines
          and preceding them with "> ", but such decisions are up
          to the implementation. Note that as with the
          justification commands, the excerpt command implicitly
          begins and ends with a line break if one is not already
          there. Nested "excerpt" commands are acceptable and
          should be interpreted as meaning that the excerpted text
          was excerpted from yet another source. Again, this can be
          displayed using additional indentation, different colors,
          etc.

          Optionally, the "excerpt" command can take a parameter by
          using the "param" command. The format of the data is
          unspecified, but it is intended to uniquely identify the
          text from which the excerpt is taken. With this
          information, an implementation should be able to uniquely
          identify the source of any particular excerpt, especially
          if two or more excerpts in the message are from the same
          source, and display it in some way that makes this
          apparent to the user.

     Lang
          causes the affected text to be interpreted as belonging
          to a particular language. This is most useful when two
          different languages use the same character set, but may
          require a different font or formatting depending on the
          language. For instance, Chinese and Japanese share



Resnick & Walker             Informational                      [Page 9]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


          similar character glyphs, and in some character sets like
          UNICODE share common code points, but it is considered
          very important that different fonts be used for the two
          languages, especially if they appear together, so that
          meaning is not lost. Also, language information can be
          used to allow for fancier text handling, like spell
          checking or hyphenation.

          The "lang" command requires a parameter using the "param"
          command. The parameter data can be any of the language
          tags specified in [RFC-1766], "Tags for the
          Identification of Languages". These tags are the two
          letter language codes taken from [ISO-639] or can be
          other language codes that are registered according to the
          instructions in the Langauge Tags RFC. Consult that memo
          for further information.

Balancing and Nesting of Formatting Commands

   Pairs of formatting commands must be properly balanced and nested.
   Thus, a proper way to describe text in bold italics is:

     <bold><italic>the-text</italic></bold>

   or, alternately,

     <italic><bold>the-text</bold></italic>

   but, in particular, the following is illegal text/enriched:

     <bold><italic>the-text</bold></italic>

   The nesting requirement for formatting commands imposes a slightly
   higher burden upon the composers of text/enriched bodies, but
   potentially simplifies text/enriched displayers by allowing them to
   be stack-based. The main goal of text/enriched is to be simple enough
   to make multifont, formatted email widely readable, so that those
   with the capability of sending it will be able to do so with
   confidence. Thus slightly increased complexity in the composing
   software was deemed a reasonable tradeoff for simplified reading
   software. Nonetheless, implementors of text/enriched readers are
   encouraged to follow the general Internet guidelines of being
   conservative in what you send and liberal in what you accept. Those
   implementations that can do so are encouraged to deal reasonably with
   improperly nested text/enriched data.






Resnick & Walker             Informational                     [Page 10]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


Unrecognized formatting commands

   Implementations must regard any unrecognized formatting command as
   "no-op" commands, that is, as commands having no effect, thus
   facilitating future extensions to "text/enriched". Private extensions
   may be defined using formatting commands that begin with "X-", by
   analogy to Internet mail header field names.

   In order to formally define extended commands, a new Internet
   document should be published.

White Space in Text/enriched Data

   No special behavior is required for the SPACE or TAB (HT) character.
   It is recommended, however, that, at least when fixed-width fonts are
   in use, the common semantics of the TAB (HT) character should be
   observed, namely that it moves to the next column position that is a
   multiple of 8. (In other words, if a TAB (HT) occurs in column n,
   where the leftmost column is column 0, then that TAB (HT) should be
   replaced by 8-(n mod 8) SPACE characters.) It should also be noted
   that some mail gateways are notorious for losing (or, less commonly,
   adding) white space at the end of lines, so reliance on SPACE or TAB
   characters at the end of a line is not recommended.

Initial State of a text/enriched interpreter

   Text/enriched is assumed to begin with filled text in a variable-
   width font in a normal typeface and a size that is average for the
   current display and user. The left and right margins are assumed to
   be maximal, that is, at the leftmost and rightmost acceptable
   positions.

Non-ASCII character sets

   One of the great benefits of MIME is the ability to use different
   varieties of non-ASCII text in messages. To use non-ASCII text in a
   message, normally a charset parameter is specified in the Content-
   type line that indicates the character set being used. For purposes
   of this RFC, any legal MIME charset parameter can be used with the
   text/enriched Content-type. However, there are two difficulties that
   arise with regard to the text/enriched Content-type when non-ASCII
   text is desired. The first problem involves difficulties that occur
   when the user wishes to create text which would normally require
   multiple non-ASCII character sets in the same text/enriched message.
   The second problem is an ambiguity that arises because of the
   text/enriched use of the "<" character in formatting commands.





Resnick & Walker             Informational                     [Page 11]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


Using multiple non-ASCII character sets

   Normally, if a user wishes to produce text which contains characters
   from entirely different character sets within the same MIME message
   (for example, using Russian Cyrillic characters from ISO 8859-5 and
   Hebrew characters from ISO 8859-8), a multipart message is used.
   Every time a new character set is desired, a new MIME body part is
   started with different character sets specified in the charset
   parameter of the Content-type line. However, using multiple character
   sets this way in text/enriched messages introduces problems. Since a
   change in the charset parameter requires a new part, text/enriched
   formatting commands used in the first part would not be able to apply
   to text that occurs in subsequent parts. It is not possible for
   text/enriched formatting commands to apply across MIME body part
   boundaries.

   [RFC-1341] attempted to get around this problem in the now obsolete
   text/richtext format by introducing different character set
   formatting commands like "iso-8859-5" and "us-ascii". But this, or
   even a more general solution along the same lines, is still
   undesirable: It is common for a MIME application to decide, for
   example, what character font resources or character lookup tables it
   will require based on the information provided by the charset
   parameter of the Content-type line, before it even begins to
   interpret or display the data in that body part. By allowing the
   text/enriched interpreter to subsequently change the character set,
   perhaps to one completely different from the charset specified in the
   Content-type line (with potentially much different resource
   requirements), too much burden would be placed on the text/enriched
   interpreter itself.

   Therefore, if multiple types of non-ASCII characters are desired in a
   text/enriched document, one of the following two methods must be
   used:

   1. For cases where the different types of non-ASCII text can be
      limited to their own paragraphs with distinct formatting, a
      multipart message can be used with each part having a
      Content-Type of text/enriched and a different charset parameter.
      The one caveat to using this method is that each new part must
      start in the initial state for a text/enriched document. That
      means that all of the text/enriched commands in the preceding
      part must be properly balanced with ending commands before the
      next text/enriched part begins. Also, each text/enriched part
      must begin a new paragraph.






Resnick & Walker             Informational                     [Page 12]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


   2. If different types of non-ASCII text are to appear in the same
      line or paragraph, or if text/enriched formatting (e.g. margins,
      typeface, justification) is required across several different
      types of non-ASCII text, a single text/enriched body part should
      be used with a character set specified that contains all of the
      required characters. For example, a charset parameter of
      "UNICODE-1-1-UTF-7" as specified in [RFC-1642] could be used for
      such purposes. Not only does UNICODE contain all of the
      characters that can be represented in all of the other registered
      ISO 8859 MIME character sets, but UTF-7 is fully compatible with
      other aspects of the text/enriched standard, including the use of
      the "<" character referred to below. Any other character sets
      that are specified for use in MIME which contain different types
      of non-ASCII text can also be used in these instances.

Use of the "<" character in formatting commands

   If the character set specified by the charset parameter on the
   Content-type line is anything other than "US-ASCII", this means that
   the text being described by text/enriched formatting commands is in a
   non-ASCII character set. However, the commands themselves are still
   the same ASCII commands that are defined in this document. This
   creates an ambiguity only with reference to the "<" character, the
   octet with numeric value 60. In single byte character sets, such as
   the ISO-8859 family, this is not a problem; the octet 60 can be
   quoted by including it twice, just as for ASCII. The problem is more
   complicated, however, in the case of multi-byte character sets, where
   the octet 60 might appear at any point in the byte sequence for any
   of several characters.

   In practice, however, most multi-byte character sets address this
   problem internally. For example, the UNICODE character sets can use
   the UTF-7 encoding which preserves all of the important ASCII
   characters in their single byte form. The ISO-2022 family of
   character sets can use certain character sequences to switch back
   into ASCII at any moment.  Therefore it is specified that, before
   text/enriched formatting commands, the prevailing character set
   should be "switched back" into ASCII, and that only those characters
   which would be interpreted as "<" in plain text should be interpreted
   as token delimiters in text/enriched.

   The question of what to do for hypothetical future character sets
   that do not subsume ASCII is not addressed in this memo.








Resnick & Walker             Informational                     [Page 13]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


Minimal text/enriched conformance

   A minimal text/enriched implementation is one that converts "<<" to
   "<", removes everything between a <param> command and the next
   balancing </param> command, removes all other formatting commands
   (all text enclosed in angle brackets), and, outside of <nofill>
   environments, converts any series of n CRLFs to n-1 CRLFs, and
   converts any lone CRLF pairs to SPACE.

Notes for Implementors

   It is recognized that implementors of future mail systems will want
   rich text functionality far beyond that currently defined for
   text/enriched.  The intent of text/enriched is to provide a common
   format for expressing that functionality in a form in which much of
   it, at least, will be understood by interoperating software. Thus, in
   particular, software with a richer notion of formatted text than
   text/enriched can still use text/enriched as its basic
   representation, but can extend it with new formatting commands and by
   hiding information specific to that software system in text/enriched
   <param> constructs. As such systems evolve, it is expected that the
   definition of text/enriched will be further refined by future
   published specifications, but text/enriched as defined here provides
   a platform on which evolutionary refinements can be based.

   An expected common way that sophisticated mail programs will generate
   text/enriched data is as part of a multipart/alternative construct.
   For example, a mail agent that can generate enriched mail in ODA
   format can generate that mail in a more widely interoperable form by
   generating both text/enriched and ODA versions of the same data,
   e.g.:

     Content-type: multipart/alternative; boundary=foo

     --foo
     Content-type: text/enriched

     [text/enriched version of data]
     --foo Content-type: application/oda

     [ODA version of data]
     --foo--

   If such a message is read using a MIME-conformant mail reader that
   understands ODA, the ODA version will be displayed; otherwise, the
   text/enriched version will be shown.





Resnick & Walker             Informational                     [Page 14]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


   In some environments, it might be impossible to combine certain
   text/enriched formatting commands, whereas in others they might be
   combined easily. For example, the combination of <bold> and <italic>
   might produce bold italics on systems that support such fonts, but
   there exist systems that can make text bold or italicized, but not
   both. In such cases, the most recently issued (innermost) recognized
   formatting command should be preferred.

   One of the major goals in the design of text/enriched was to make it
   so simple that even text-only mailers will implement enriched-to-
   plain-text translators, thus increasing the likelihood that enriched
   text will become "safe" to use very widely. To demonstrate this
   simplicity, an extremely simple C program that converts text/enriched
   input into plain text output is included in Appendix A.

Extensions to text/enriched

   It is expected that various mail system authors will desire
   extensions to text/enriched. The simple syntax of text/enriched, and
   the specification that unrecognized formatting commands should simply
   be ignored, are intended to promote such extensions.

An Example

   Putting all this together, the following "text/enriched" body
   fragment:

     From: Nathaniel Borenstein <nsb@bellcore.com>
     To: Ned Freed <ned@innosoft.com>
     Content-type: text/enriched

     <bold>Now</bold> is the time for <italic>all</italic>
     good men
     <smaller>(and <<women>)</smaller> to
     <ignoreme>come</ignoreme>

     to the aid of their


     <color><param>red</param>beloved</color>
     country.

     By the way,
     I think that <paraindent><param>left</param><<smaller>

     </paraindent>should REALLY be called

     <paraindent><param>left</param><<tinier></paraindent>



Resnick & Walker             Informational                     [Page 15]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


     and that I am always right.

     -- the end

   represents the following formatted text (which will, no doubt, look
   somewhat cryptic in the text-only version of this document):

     Now is the time for all good men (and <women>) to come
     to the aid of their

     beloved country.
     By the way, I think that
          <smaller>
     should REALLY be called
          <tinier>
     and that I am always right.
     -- the end

   where the word "beloved" would be in red on a color display.

   ti 0 Security Considerations

   Security issues are not discussed in this memo, as the mechanism
   raises no security issues.

Authors' Addresses

   For more information, the authors of this document may be contacted
   via Internet mail:

   Peter W. Resnick
   QUALCOMM Incorporated
   6455 Lusk Boulevard
   San Diego, CA 92121-2779

   Phone: +1 619 587 1121
   Fax: +1 619 658 2230
   EMail: presnick@qualcomm.com


   Amanda Walker
   InterCon Systems Corporation
   950 Herndon Parkway
   Herndon, VA 22070

   Phone: +1 703 709 5500
   Fax: +1 703 709 5555
   EMail: amanda@intercon.com



Resnick & Walker             Informational                     [Page 16]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


Acknowledgements

   The authors gratefully acknowledge the input of many contributors,
   readers, and implementors of the specification in this document.
   Particular thanks are due to Nathaniel Borenstein, the original
   author of RFC 1563.

References

   [RFC-1341]
        Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail
        Extensions): Mechanisms for Specifying and Describing the Format
        of Internet Message Bodies", 06/11/1992.

   [RFC-1521]
        Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail
        Extensions) Part One: Mechanisms for Specifying and Describing
        the Format of Internet Message Bodies", 09/23/1993.

   [RFC-1523]
        Borenstein, N., "The text/enriched MIME Content-type",
        09/23/1993.

   [RFC-1563]
        Borenstein, N., "The text/enriched MIME Content-type",
        01/10/1994.

   [RFC-1642]
        Goldsmith, D., Davis, M., "UTF-7 - A Mail-Safe Transformation
        Format of Unicode", 07/13/1994.

   [RFC-1766]
        Alvestrand, H., "Tags for the Identification of Languages",
        03/02/1995.

   [RFC-1866]
        Berners-Lee, T., and D. Connolly, D., "Hypertext Markup Language
        - 2.0", 11/03/1995.













Resnick & Walker             Informational                     [Page 17]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


Appendix A--A Simple enriched-to-plain Translator in C

   One of the major goals in the design of the text/enriched subtype of
   the text Content-Type is to make formatted text so simple that even
   text-only mailers will implement enriched-to-plain-text translators,
   thus increasing the likelihood that multifont text will become "safe"
   to use very widely. To demonstrate this simplicity, what follows is a
   simple C program that converts text/enriched input into plain text
   output. Note that the local newline convention (the single character
   represented by "\n") is assumed by this program, but that special
   CRLF handling might be necessary on some systems.

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

main() {
    int c, i, paramct=0, newlinect=0, nofill=0;
    char token[62], *p;

    while ((c=getc(stdin)) != EOF) {
        if (c == '<') {
            if (newlinect == 1) putc(' ', stdout);
            newlinect = 0;
            c = getc(stdin);
            if (c == '<') {
                if (paramct <= 0) putc(c, stdout);
            } else {
                ungetc(c, stdin);
                for (i=0, p=token;
                    (c=getc(stdin)) != EOF && c != '>'; i++) {
                    if (i < sizeof(token)-1)
                        *p++ = isupper(c) ? tolower(c) : c;
                }
                *p = '\0';
                if (c == EOF) break;
                if (strcmp(token, "param") == 0)
                    paramct++;
                else if (strcmp(token, "nofill") == 0)
                    nofill++;
                else if (strcmp(token, "/param") == 0)
                    paramct--;
                else if (strcmp(token, "/nofill") == 0)
                    nofill--;
            }
        } else {
            if (paramct > 0)



Resnick & Walker             Informational                     [Page 18]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


                ; /* ignore params */
            else if (c == '\n' && nofill <= 0) {
                if (++newlinect > 1) putc(c, stdout);
            } else {
                if (newlinect == 1) putc(' ', stdout);
                newlinect = 0;
                putc(c, stdout);
            }
        }
    }
    /* The following line is only needed with line-buffering */
    putc('\n', stdout);
    exit(0);
}

   It should be noted that one can do considerably better than this in
   displaying text/enriched data on a dumb terminal. In particular, one
   can replace font information such as "bold" with textual emphasis
   (like *this* or _T_H_I_S_). One can also properly handle the
   text/enriched formatting commands regarding indentation,
   justification, and others.  However, the above program is all that is
   necessary in order to present text/enriched on a dumb terminal
   without showing the user any formatting artifacts.

Appendix B--A Simple enriched-to-HTML Translator in C

   It is fully expected that other text formatting standards like HTML
   and SGML will supplant text/enriched in Internet mail. It is also
   likely that as this happens, recipients of text/enriched mail will
   wish to view such mail with an HTML viewer. To this end, the
   following is a simple example of a C program to convert text/enriched
   to HTML. Since the current version of HTML at the time of this
   document's publication is HTML 2.0 defined in [RFC-1866], this
   program converts to that standard.  There are several text/enriched
   commands that have no HTML 2.0 equivalent. In those cases, this
   program simply puts those commands into processing instructions; that
   is, surrounded by "<?" and ">". As in Appendix A, the local newline
   convention (the single character represented by "\n") is assumed by
   this program, but special CRLF handling might be necessary on some
   systems.

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

main() {
    int c, i, paramct=0, nofill=0;



Resnick & Walker             Informational                     [Page 19]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


    char token[62], *p;

    while((c=getc(stdin)) != EOF) {
        if(c == '<') {
            c = getc(stdin);
            if(c == '<') {
                fputs("&lt;", stdout);
            } else {
                ungetc(c, stdin);
                for (i=0, p=token;
                    (c=getc(stdin)) != EOF && c != '>'; i++) {
                    if (i < sizeof(token)-1)
                        *p++ = isupper(c) ? tolower(c) : c;
                }
                *p = '\0';
                if(c == EOF) break;
                if(strcmp(token, "/param") == 0) {
                    paramct--;
                    putc('>', stdout);
                } else if(paramct > 0) {
                    fputs("&lt;", stdout);
                    fputs(token, stdout);
                    fputs("&gt;", stdout);
                } else {
                    putc('<', stdout);
                    if(strcmp(token, "nofill") == 0) {
                        nofill++;
                        fputs("pre", stdout);
                    } else if(strcmp(token, "/nofill") == 0) {
                        nofill--;
                        fputs("/pre", stdout);
                    } else if(strcmp(token, "bold") == 0) {
                        fputs("b", stdout);
                    } else if(strcmp(token, "/bold") == 0) {
                        fputs("/b", stdout);
                    } else if(strcmp(token, "italic") == 0) {
                        fputs("i", stdout);
                    } else if(strcmp(token, "/italic") == 0) {
                        fputs("/i", stdout);
                    } else if(strcmp(token, "fixed") == 0) {
                        fputs("tt", stdout);
                    } else if(strcmp(token, "/fixed") == 0) {
                        fputs("/tt", stdout);
                    } else if(strcmp(token, "excerpt") == 0) {
                        fputs("blockquote", stdout);
                    } else if(strcmp(token, "/excerpt") == 0) {
                        fputs("/blockquote", stdout);
                    } else {



Resnick & Walker             Informational                     [Page 20]
^L
RFC 1896            text/enriched MIME Content-type        February 1996


                        putc('?', stdout);
                        fputs(token, stdout);
                        if(strcmp(token, "param") == 0) {
                            paramct++;
                            putc(' ', stdout);
                            continue;
                        }
                    }
                    putc('>', stdout);
                }
            }
        } else if(c == '>') {
            fputs("&gt;", stdout);
        } else if (c == '&') {
            fputs("&amp;", stdout);
        } else {
            if(c == '\n' && nofill <= 0 && paramct <= 0) {
                while((i=getc(stdin)) == '\n') fputs("<br>", stdout);
                ungetc(i, stdin);
            }
            putc(c, stdout);
        }
    }
    /* The following line is only needed with line-buffering */
    putc('\n', stdout);
    exit(0);
}
























Resnick & Walker             Informational                     [Page 21]
^L