(per RFC4263)
Type name: text
Subtype name: troff
Required parameters: none
Optional parameters:
charset: Must be a charset registered for use with MIME text types
[N3.RFC2046], except where transport protocols are explicitly
exempted from that restriction. Specifies the charset of the
media content. With traditional source content, this will be
the default "US-ASCII" charset. Some recent versions of troff
processing software can handle Unicode input charsets; however,
there may be interoperability issues if the input uses such a
charset (see "Interoperability considerations" below).
process: Human-readable additional information for formatting,
including environment variables, preprocessor arguments and
order, formatter arguments, and postprocessors. The parameter
value may need to be quoted or encoded as provided for by
[N4.RFC2045] as amended by [N5.RFC2231] and [N6.Errata].
Generating implementations must not encode executable content
and other implementations must not attempt any execution or
other interpretation of the parameter value, as the parameter
value may be prose text. Implementations SHOULD present the
parameter (after reassembly of continuation parameters, etc.)
as information related to the media type, particularly if the
media content is not immediately available (e.g., as with
message/external-body composite media [N3.RFC2046]).
resources: Lists any additional files or programs that are
required for formatting (e.g., via .cf, .nx, .pi, .so, and/or
.sy directives).
versions: Human-readable indication of any known specific versions
of preprocessors, formatter, macro packages, postprocessors,
etc., required to process the content.
Encoding considerations:
7bit is adequate for traditional troff provided line endings are
canonicalized per [N3.RFC2046]. Transfer of this media type
content via some transport mechanisms may require or benefit
from encoding into a 7bit range via a suitable encoding method
such as the ones described in [N4.RFC2045]. In particular,
some lines in this media type might begin or end with
whitespace, and that leading and/or trailing whitespace might
be discarded or otherwise mangled if the media type is not
encoded for transport.
8bit may be used with Unicode characters represented as a series
of octets using the utf-8 charset [I4.RFC3629], where transport
methods permit 8bit content and where content line length is
suitable. Transport encoding considerations for robustness may
also apply, and if a suitable 8bit encoding mechanism is
standardized, it might be applicable for protection of media
during transport.
binary may be necessary when raw Unicode is used or where line
lengths exceed the allowable maximum for 7bit and 8bit content
[N4.RFC2045], and may be used in environments (e.g., HTTP
[I5.RFC2616]) where Unicode characters may be transferred via a
non-MIME charset such as UTF-16 [I6.RFC2781].
framed encoding MAY be used, but is not required and is not
generally useful with this media type.
Restrictions on usage: none
Security considerations: Some troff directives (.sy and .pi) can
cause arbitrary external programs to be run. Several troff
directives (.so, .nx, and .cf) may read external files (and/or
devices on systems that support device input via file system
semantics) during processing. Several preprocessors have similar
features. Some implementations have a "safe" mode that disables
some of these features. Formatters and preprocessors are
programmable, and it is possible to provide input which specifies
an infinite loop, which could result in denial of service, even in
implementations that restrict use of directives that access
external resources. Users of this media type SHOULD be vigilant
of the potential for damage that may be caused by careless
processing of media obtained from untrusted sources.
Processing of this media type other than by facilities that strip
or ignore potentially dangerous directives, and processing by
preprocessors and/or postprocessors, SHOULD NOT be invoked
automatically (i.e., without user confirmation). In some cases,
as this is a text media type (i.e., it contains text that is
comprehensible without processing), it may be sufficient to
present the media type with no processing at all. However, like
any other text media, this media type may contain control
characters, and implementers SHOULD take precautions against
untoward consequences of sending raw control characters to display
devices.
Users of this media type SHOULD carefully scrutinize suggested
command lines associated with the "process" parameter, contained
in comments within the media, or conveyed via external mechanisms,
both for attempts at social engineering and for the effects of
ill-considered values of the parameter. While some
implementations may have "safe" modes, those using this media type
MUST NOT presume that they are available or active.
Comments may be included in troff source; comments are not
formatted for output. However, they are of course readable in the
troff document source. Authors should be careful about
information placed in comments, as such information may result in
a leak of information, or may have other undesirable consequences.
While it is possible to overlay text with graphics or otherwise
produce formatting instructions that would visually obscure text
when formatted, such measures do not prevent extracting text from
the document source, and might be ineffective in obscuring text
when formatted electronically, e.g., as PostScript or PDF.
Interoperability considerations: Recent implementations of
formatters, macro packages, and preprocessors may include some
extended capabilities that are not present in earlier
implementations. Use of such extensions obviously limits the
ability to produce consistent formatted output at sites with
implementations that do not support those extensions. Use of any
such extensions in a particular document using this media type
SHOULD be indicated via the "versions" parameter value.
As mentioned in the Introduction, macro packages are troff
documents, and their content may be subject to copyright. That
has led to multiple independent implementations of macro packages,
which may exhibit gross or subtle differences with some content.
Some preprocessors or postprocessors might be unavailable at some
sites. Where some implementation is available, there may be
differences in implementation that affect the output produced.
For example, some versions of the "pic" preprocessor provide the
capability to fill a bounded graphical object; others lack that
capability. Of those that support that feature, there are
differences in whether a solid fill is represented by a value of
0.0 vs. 1.0. Some implementations support only gray-scale output;
others support color.
Preprocessors or postprocessors may depend on additional programs
such as awk, and implementation differences (including bugs) may
lead to different results on different systems (or even on the
same system with a different environment).
There is a wide variation in the capabilities of various
presentation media and the devices used to prepare content for
presentation. Indeed, that is one reason that there are two basic
formatter program types (nroff for output where limited formatting
control is available, and troff where a greater range of control
is possible). Clearly, a document designed to use complex or
sophisticated formatting might not be representable in simpler
media or with devices lacking certain capabilities. Often it is
possible to produce a somewhat inferior approximation; colors
might be represented as gray-scale values, accented characters
might be produced by overstriking, italics might be represented by
underlining, etc.
Various systems store text with different line ending codings.
For the purpose of transferring this media type between systems or
between applications using MIME methods, line endings MUST use the
canonical CRLF line ending per [N3.RFC2046].
Published specification: [N1.CSTR54]
Applications which use this media type: The following applications in
each sub-category are examples. The lists are not intended to be
exhaustive.
Preprocessors: tbl [I7.CSTR49], grap [I8.CSTR114], pic
[I9.CSTR116], chem [I10.CSTR122], eqn [I11.eqn], dformat
[I12.CSTR142]
Formatters: troff, nroff, Eroff, sqtroff, groff, awf, cawf
Format converters: deroff, troffcvt, unroff, troff2html, mm2html
Macro packages: man [I13.UNIXman1], me [I14.me], mm
[I15.DWBguide], ms [I16.ms], mv [I15.DWBguide], rfc
[I2.Lilly05]
Additional information:
Magic number(s): None; however, the content format is distinctive
(see "Published specification").
File extension(s): Files do not require any specific "extension".
Many are in use as a convenience for mechanized processing of
files, some associated with specific macro packages or
preprocessors; others are ad hoc. File names are orthogonal to
the nature of the content. In particular, while a file name or
a component of a name may be useful in some types of automated
processing of files, the name or component might not be capable
of indicating subtleties such as proportion of textual (as
opposed to image or formatting directive) content. This media
type SHOULD NOT be assigned a relationship with any file
"extension" where content may be untrusted unless there is
provision for human judgment that may be used to override that
relationship for individual files. Where appropriate, a file
name MAY be suggested by a suitable mechanism such as the one
specified in [I17.RFC2183] as amended by [N5.RFC2231] and
[N6.Errata].
Macintosh File Type Code(s): unknown
Person & email address to contact for further information:
Bruce Lilly
blilly&erols.com
Intended usage: COMMON
Author/Change controller: IESG
Consistency: The media has provision for comments; these are
sometimes used to convey recommended processing commands, to
indicate required resources, etc. To avoid confusing recipients,
senders SHOULD ensure that information specified in optional
parameters is consistent with any related information that may be
contained within the media content.