(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.