# groff_out - GNU roff intermediate output format - man(5) - [phpMan] [_groff_out_(5)](https://www.chedong.com/phpMan.php/man/groffout/5/markdown) File Formats Manual [_groff_out_(5)](https://www.chedong.com/phpMan.php/man/groffout/5/markdown) ## Name groff_out - GNU _roff_ intermediate output format ## Description The fundamental operation of the [_troff_(1)](https://www.chedong.com/phpMan.php/man/troff/1/markdown) formatter is the translation of the [_groff_(7)](https://www.chedong.com/phpMan.php/man/groff/7/markdown) input language into a series of instructions concerned primarily with placing glyphs or geometric objects at specific positions on a rectangular page. In the following discussion, the term _command_ refers to this intermediate output language, never to the [_groff_(7)](https://www.chedong.com/phpMan.php/man/groff/7/markdown) language intended for use by document authors. Intermediate output commands comprise several categories: glyph output; font, color, and text size selection; motion of the printing position; page advance‐ ment; drawing of geometric primitives; and device control commands, a catch-all for other op‐ erations. The last includes directives to start and stop output, identify the intended out‐ put device, and embed URL hyperlinks in supported output formats. Because the front-end command [_groff_(1)](https://www.chedong.com/phpMan.php/man/groff/1/markdown) is a wrapper that normally runs the _troff_ formatter to generate intermediate output and an output driver (“postprocessor”) to consume it, users nor‐ mally do not encounter this language. The _groff_ program's **-Z **option inhibits postprocessing such that this intermediate output is sent to the standard output stream as when _troff_ is run manually. _groff_'s intermediate output facilitates the development of output drivers and other post‐ processors by offering a common programming interface. It is an extension of the page de‐ scription language developed by Brian Kernighan for AT&T device-independent _troff_ circa 1980. Where a distinction is necessary, we will say “_troff_ output” to describe the output of GNU _troff_, and “intermediate output” to denote the language accepted by the parser implemented in _groff_'s internal C++ library used by most of its output drivers. ## Language concepts During the run of _troff_, the _roff_ input is cracked down to the information on what has to be printed at what position on the intended device. So the language of the _intermediate_ _output_ format can be quite small. Its only elements are commands with or without arguments. In this document, the term “command” always refers to the _intermediate_ _output_ language, never to the _roff_ language used for document formatting. There are commands for positioning and text writing, for drawing, and for device controlling. ### Separation _Classical_ _troff_ _output_ had strange requirements on whitespace. The _groff_ output parser, how‐ ever, is smart about whitespace by making it maximally optional. The whitespace characters, i.e., the _tab_, _space_, and _newline_ characters, always have a syntactical meaning. They are never printable because spacing within the output is always done by positioning commands. Any sequence of _space_ or _tab_ characters is treated as a single _syntactical_ _space_. It sepa‐ rates commands and arguments, but is only required when there would occur a clashing between the command code and the arguments without the space. Most often, this happens when variable length command names, arguments, argument lists, or command clusters meet. Commands and ar‐ guments with a known, fixed length need not be separated by _syntactical_ _space_. A line break is a syntactical element, too. Every command argument can be followed by white‐ space, a comment, or a newline character. Thus a _syntactical_ _line_ _break_ is defined to con‐ sist of optional _syntactical_ _space_ that is optionally followed by a comment, and a newline character. The normal commands, those for positioning and text, consist of a single letter taking a fixed number of arguments. For historical reasons, the parser allows stacking of such com‐ mands on the same line, but fortunately, in _groff_ _intermediate_ _output_, every command with at least one argument is followed by a line break, thus providing excellent readability. The other commands — those for drawing and device controlling — have a more complicated structure; some recognize long command names, and some take a variable number of arguments. So all **D **and **x **commands were designed to request a _syntactical_ _line_ _break_ after their last argument. Only one command, ‘**x X**’ has an argument that can stretch over several lines, all other commands must have all of their arguments on the same line as the command, i.e., the arguments may not be split by a line break. Lines containing only spaces and/or a comment are treated as empty and ignored. ### Argument units Some commands accept integer arguments that represent measurements, but the scaling units of the formatter's language are never used. Most commands assume a scaling unit of “**u**” (basic units), and others use “**z**” (scaled points); These are defined by the parameters specified in the device's _DESC_ file; see [_groff_font_(5)](https://www.chedong.com/phpMan.php/man/grofffont/5/markdown) and, for more on scaling units, [_groff_(7)](https://www.chedong.com/phpMan.php/man/groff/7/markdown) and _Groff:_ _The_ _GNU_ _Implementation_ _of_ _troff_, the _groff_ Texinfo manual. Color-related commands use dimen‐ sionless integers. Note that single characters can have the eighth bit set, as can the names of fonts and spe‐ cial characters (this is, glyphs). The names of glyphs and fonts can be of arbitrary length. A glyph that is to be printed will always be in the current font. A string argument is always terminated by the next whitespace character (space, tab, or new‐ line); an embedded **# **character is regarded as part of the argument, not as the beginning of a comment command. An integer argument is already terminated by the next non-digit character, which then is regarded as the first character of the next argument or command. ### Document parts A correct _intermediate_ _output_ document consists of two parts, the _prologue_ and the _body_. The task of the _prologue_ is to set the general device parameters using three exactly speci‐ fied commands. The _groff_ _prologue_ is guaranteed to consist of the following three lines (in that order): **x T _**device_ **x res _**n_ _h_ _v_ **x init** with the arguments set as outlined in subsection “Device Control Commands” below. However, the parser for the _intermediate_ _output_ format is able to swallow additional whitespace and comments as well. The _body_ is the main section for processing the document data. Syntactically, it is a se‐ quence of any commands different from the ones used in the _prologue_. Processing is termi‐ nated as soon as the first **x stop **command is encountered; the last line of any _groff_ _interme‐_ _diate_ _output_ always contains such a command. Semantically, the _body_ is page oriented. A new page is started by a **p **command. Positioning, writing, and drawing commands are always done within the current page, so they cannot occur before the first **p **command. Absolute positioning (by the **H **and **V **commands) is done relative to the current page, all other positioning is done relative to the current location within this page. ## Command reference This section describes all _intermediate_ _output_ commands, the classical commands as well as the _groff_ extensions. ### Comment command **#_**anything_⟨line-break⟩ A comment. Ignore any characters from the **# **character up to the next newline. Each comment can be preceded by arbitrary _syntactical_ _space_; every command can be termi‐ nated by a comment. ### Simple commands The commands in this subsection have a command code consisting of a single character, taking a fixed number of arguments. Most of them are commands for positioning and text writing. These commands are smart about whitespace. Optionally, _syntactical_ _space_ can be inserted be‐ fore, after, and between the command letter and its arguments. All of these commands are stackable, i.e., they can be preceded by other simple commands or followed by arbitrary other commands on the same line. A separating _syntactical_ _space_ is necessary only when two integer arguments would clash or if the preceding argument ends with a string argument. **C _**id_⟨white-space⟩ Typeset the glyph of the special character _id_. Trailing syntactical space is neces‐ sary to allow special character names of arbitrary length. The drawing position is not advanced. **c _**c_ Typeset the glyph of the ordinary character character _c_. The drawing position is not advanced. **f _**n_ Select the font mounted at position _n_. _n_ cannot be negative. **H _**n_ Horizontally move the drawing position to _n_ basic units from the left edge of the page. _n_ cannot be negative. **h _**n_ Move the drawing position right _n_ basic units. AT&T _troff_ allowed negative _n;_ GNU _troff_ does not produce such values, but _groff_'s output driver library handles them. **m _**scheme_ [_component_ ...] Select the stroke color using the _component_s in the color space _scheme_. Each _compo‐_ _nent_ is an integer between 0 and 65536. The quantity of components and their meanings vary with each _scheme_. This command is a _groff_ extension. **mc _**cyan_ _magenta_ _yellow_ Use the CMY color scheme with components cyan, magenta, and yellow. **md **Use the default color (no components; black in most cases). **mg _**gray_ Use a grayscale color scheme with a component ranging between 0 (black) and 65536 (white). **mk _**cyan_ _magenta_ _yellow_ _black_ Use the CMYK color scheme with components cyan, magenta, yellow, and black. **mr _**red_ _green_ _blue_ Use the RGB color scheme with components red, green, and blue. **N _**n_ Typeset the glyph with index _n_ in the current font. _n_ is normally a non-negative in‐ teger. The drawing position is not advanced. The **html **and **xhtml **devices use this command with negative _n_ to produce unbreakable space; the absolute value of _n_ is taken and interpreted in basic units. **n _**b_ _a_ Indicate a break. No action is performed; the command is present to make the output more easily parsed. The integers _b_ and _a_ describe the vertical space amounts before and after the break, respectively. GNU _troff_ issues this command but _groff_'s output driver library ignores it. See **v **and **V**. **p _**n_ Begin a new page, setting its number to _n_. Each page is independent, even from those using the same number. The vertical drawing position is set to 0. All positioning, writing, and drawing commands are interpreted in the context of a page, so a **p **command must precede them. **s _**n_ Set type size to _n_ scaled points (unit **z **in GNU _troff_). AT&T _troff_ used unscaled points (**p**) instead; see section “Compatibility” below. **t _**xyz_...⟨white-space⟩ **t _**xyz_... _dummy-arg_⟨white-space⟩ Typeset word _xyz_; that is, set a sequence of ordinary glyphs named _x_, _y_, _z_, ..., ter‐ minated by a space or newline; an optional second integer argument is ignored (this allows the formatter to generate an even number of arguments). Each glyph is set at the current drawing position, and the position is then advanced horizontally by the glyph's width. A glyph's width is read from its metrics in the font description file, scaled to the current type size, and rounded to a multiple of the horizontal motion quantum. Use the **C **command to emplace glyphs of special characters. The **t **command is a _groff_ extension and is output only for devices whose _DESC_ file contains the **tcommand** directive; see [_groff_font_(5)](https://www.chedong.com/phpMan.php/man/grofffont/5/markdown). **u _**n_ _xyz_... **u _**xyz_... _dummy-arg_⟨white-space⟩ Typeset word _xyz_ with track kerning. As **t**, but after placing each glyph, the drawing position is further advanced horizontally by _n_ basic units. The **u **command is a _groff_ extension and is output only for devices whose _DESC_ file contains the **tcommand **direc‐ tive; see [_groff_font_(5)](https://www.chedong.com/phpMan.php/man/grofffont/5/markdown). **V _**n_ Vertically move the drawing position to _n_ basic units from the top edge of the page. _n_ cannot be negative. **v _**n_ Move the drawing position down _n_ basic units. AT&T _troff_ allowed negative _n;_ GNU _troff_ does not produce such values, but _groff_'s output driver library handles them. **w **Indicate an inter-word space. No action is performed; the command is present to make the output more easily parsed. Only adjustable, breakable inter-word spaces are thus described; those resulting from **\~ **or horizontal motion escape sequences are not. GNU _troff_ issues this command but _groff_'s output driver library ignores it. See **h **and **H**. ### Graphics commands Each graphics or drawing command in the _intermediate_ _output_ starts with the letter **D **followed by one or two characters that specify a subcommand; this is followed by a fixed or variable number of integer arguments that are separated by a single space character. A **D **command may not be followed by another command on the same line (apart from a comment), so each **D **command is terminated by a _syntactical_ _line_ _break_. _troff_ output follows the classical spacing rules (no space between command and subcommand, all arguments are preceded by a single space character), but the parser allows optional space between the command letters and makes the space before the first argument optional. As usual, each space can be any sequence of tab and space characters. Some graphics commands can take a variable number of arguments. In this case, they are inte‐ gers representing a size measured in basic units **u**. The _h_ arguments stand for horizontal distances where positive means right, negative left. The _v_ arguments stand for vertical dis‐ tances where positive means down, negative up. All these distances are offsets relative to the current location. Unless indicated otherwise, each graphics command directly corresponds to a similar _groff_ **\D** escape sequence; see [_groff_(7)](https://www.chedong.com/phpMan.php/man/groff/7/markdown). Unknown **D **commands are assumed to be device-specific. Its arguments are parsed as strings; the whole information is then sent to the postprocessor. In the following command reference, the syntax element _⟨line-break⟩_ means a _syntactical_ _line_ _break_ as defined in subsection “Separation” above. **D~ _**h1_ _v1_ _h2_ _v2_ ... _hn_ _vn_⟨line-break⟩ Draw B-spline from current position to offset (_h1_, _v1_), then to offset (_h2_, _v2_) if given, etc., up to (_hn_, _vn_). This command takes a variable number of argument pairs; the current position is moved to the terminal point of the drawn curve. **Da _**h1_ _v1_ _h2_ _v2_⟨line-break⟩ Draw arc from current position to (_h1_, _v1_)+(_h2_, _v2_) with center at (_h1_, _v1_); then move the current position to the final point of the arc. **DC _**d_⟨line-break⟩ **DC _**d_ _dummy-arg_⟨line-break⟩ Draw a solid circle using the current fill color with diameter _d_ (integer in basic units **u**) with leftmost point at the current position; then move the current position to the rightmost point of the circle. An optional second integer argument is ignored (this allows the formatter to generate an even number of arguments). This command is a _groff_ extension. **Dc _**d_⟨line-break⟩ Draw circle line with diameter _d_ (integer in basic units **u**) with leftmost point at the current position; then move the current position to the rightmost point of the circle. **DE _**h_ _v_⟨line-break⟩ Draw a solid ellipse in the current fill color with a horizontal diameter of _h_ and a vertical diameter of _v_ (both integers in basic units **u**) with the leftmost point at the current position; then move to the rightmost point of the ellipse. This command is a _groff_ extension. **De _**h_ _v_⟨line-break⟩ Draw an outlined ellipse with a horizontal diameter of _h_ and a vertical diameter of _v_ (both integers in basic units **u**) with the leftmost point at current position; then move to the rightmost point of the ellipse. **DF _**color-scheme_ [_component_ ...]⟨line-break⟩ Set fill color for solid drawing objects using different color schemes; the analogous command for setting the color of text, line graphics, and the outline of graphic ob‐ jects is **m**. The color components are specified as integer arguments between 0 and 65536. The number of color components and their meaning vary for the different color schemes. These commands are generated by the _groff_ escape sequences **\D'F **...**' **and **\M** (with no other corresponding graphics commands). This command is a _groff_ extension. **DFc _**cyan_ _magenta_ _yellow_⟨line-break⟩ Set fill color for solid drawing objects using the CMY color scheme, having the 3 color components cyan, magenta, and yellow. **DFd **⟨line-break⟩ Set fill color for solid drawing objects to the default fill color value (black in most cases). No component arguments. **DFg _**gray_⟨line-break⟩ Set fill color for solid drawing objects to the shade of gray given by the ar‐ gument, an integer between 0 (black) and 65536 (white). **DFk _**cyan_ _magenta_ _yellow_ _black_⟨line-break⟩ Set fill color for solid drawing objects using the CMYK color scheme, having the 4 color components cyan, magenta, yellow, and black. **DFr _**red_ _green_ _blue_⟨line-break⟩ Set fill color for solid drawing objects using the RGB color scheme, having the 3 color components red, green, and blue. **Df _**n_⟨line-break⟩ The argument _n_ must be an integer in the range -32767 to 32767. 0≤_n_≤1000 Set the color for filling solid drawing objects to a shade of gray, where 0 corresponds to solid white, 1000 (the default) to solid black, and values in between to intermediate shades of gray; this is obsoleted by command **DFg**. _n_<0 or _n_>1000 Set the filling color to the color that is currently being used for the text and the outline, see command **m**. For example, the command sequence mg 0 0 65536 Df -1 sets all colors to blue. This command is a _groff_ extension. **Dl _**h_ _v_⟨line-break⟩ Draw line from current position to offset (_h_, _v_) (integers in basic units **u**); then set current position to the end of the drawn line. **Dp _**h1_ _v1_ _h2_ _v2_ ... _hn_ _vn_⟨line-break⟩ Draw a polygon line from current position to offset (_h1_, _v1_), from there to offset (_h2_, _v2_), etc., up to offset (_hn_, _vn_), and from there back to the starting position. For historical reasons, the position is changed by adding the sum of all arguments with odd index to the current horizontal position and the even ones to the vertical position. Although this doesn't make sense it is kept for compatibility. This com‐ mand is a _groff_ extension. **DP _**h1_ _v1_ _h2_ _v2_ ... _hn_ _vn_⟨line-break⟩ The same macro as the corresponding **Dp **command with the same arguments, but draws a solid polygon in the current fill color rather than an outlined polygon. The position is changed in the same way as with **Dp**. This command is a _groff_ extension. **Dt _**n_⟨line-break⟩ Set the current line thickness to _n_ (an integer in basic units **u**) if _n_>0; if _n_=0 se‐ lect the smallest available line thickness; otherwise, the line thickness is made pro‐ portional to the type size, which is the default. For historical reasons, the hori‐ zontal position is changed by adding the argument to the current horizontal position, while the vertical position is not changed. Although this doesn't make sense, it is kept for compatibility. This command is a _groff_ extension. ### Device control commands Each device control command starts with the letter **x **followed by a space character (optional or arbitrary space/tab in _groff_) and a subcommand letter or word; each argument (if any) must be preceded by a _syntactical_ _space_. All **x **commands are terminated by a _syntactical_ _line_ _break_; no device control command can be followed by another command on the same line (except a comment). The subcommand is basically a single letter, but to increase readability, it can be written as a word, i.e., an arbitrary sequence of characters terminated by the next tab, space, or newline character. All characters of the subcommand word but the first are simply ignored. For example, _troff_ outputs the initialization command **x i **as **x init **and the resolution com‐ mand **x r **as **x res**. But writings like **x i_like_groff **and **x roff_is_groff **are accepted as well to mean the same commands. In the following, the syntax element _⟨line-break⟩_ means a _syntactical_ _line_ _break_ as defined in subsection “Separation” above. **xF _**name_⟨line-break⟩ (_Filename_ control command) Use _name_ as the intended name for the current file in error reports. This is useful for remembering the original file name when _groff_ uses an internal piping mechanism. The input file is not changed by this command. This command is a _groff_ extension. **xf _**n_ _s_⟨line-break⟩ (_font_ control command) Mount font position _n_ (a non-negative integer) with font named _s_ (a text word); see [_groff_font_(5)](https://www.chedong.com/phpMan.php/man/grofffont/5/markdown). **xH _**n_⟨line-break⟩ (_Height_ control command) Set character height to _n_ (a positive integer in scaled points **z**). _Classical_ _troff_ used the unit points (**p**) instead; see section “Compatibility” below. **xi **⟨line-break⟩ (_init_ control command) Initialize device. This is the third command of the _prologue_. **xp **⟨line-break⟩ (_pause_ control command) Parsed but ignored. The classical documentation reads _pause_ _device,_ _can_ _be_ _restarted_. **xr _**n_ _h_ _v_⟨line-break⟩ (_resolution_ control command) Resolution is _n_, while _h_ is the minimal horizontal motion, and _v_ the minimal vertical motion possible with this device; all arguments are positive integers in basic units **u** per inch. This is the second command of the _prologue_. **xS _**n_⟨line-break⟩ (_Slant_ control command) Set slant to _n_ degrees (an integer in basic units **u**). **xs **⟨line-break⟩ (_stop_ control command) Terminates the processing of the current file; issued as the last command of any _in‐_ _termediate_ _troff_ _output_. **xt **⟨line-break⟩ (_trailer_ control command) Generate trailer information, if any. In **groff**, this is currently ignored. **xT _**xxx_⟨line-break⟩ (_Typesetter_ control command) Set the name of the output driver to _xxx_, a sequence of non-whitespace characters ter‐ minated by whitespace. The possible names correspond to those of _groff_'s **-T **option. This is the first command of the prologue. **xu _**n_⟨line-break⟩ (_underline_ control command) Configure underlining of spaces. If _n_ is 1, start underlining of spaces; if _n_ is 0, stop underlining of spaces. This is needed for the **cu **request in **nroff **mode and is ignored otherwise. This command is a _groff_ extension. **xX _**anything_⟨line-break⟩ (_X-escape_ control command) Send string _anything_ uninterpreted to the device. If the line following this command starts with a **+ **character this line is interpreted as a continuation line in the fol‐ lowing sense. The **+ **is ignored, but a newline character is sent instead to the de‐ vice, the rest of the line is sent uninterpreted. The same applies to all following lines until the first character of a line is not a **+ **character. This command is gen‐ erated by the _groff_ escape sequence **\X**. The line-continuing feature is a _groff_ exten‐ sion. ### Obsolete command In _classical_ _troff_ output, emitting a single glyph was mostly done by a very strange command that combined a horizontal move and the printing of a glyph. It didn't have a command code, but is represented by a 3-character argument consisting of exactly 2 digits and a character. _ddc_ Move right _dd_ (exactly two decimal digits) basic units **u**, then print glyph with sin‐ gle-letter name _c_. In _groff_, arbitrary _syntactical_ _space_ around and within this command is allowed to be added. Only when a preceding command on the same line ends with an argument of vari‐ able length a separating space is obligatory. In _classical_ _troff_, large clusters of these and other commands were used, mostly without spaces; this made such output al‐ most unreadable. For modern high-resolution devices, this command does not make sense because the width of the glyphs can become much larger than two decimal digits. In _groff_, it is used only for output to the **X75**, **X75-12**, **X100**, and **X100-12 **devices. For others, the commands **t **and **u **provide greater functionality and superior troubleshooting capacity. ## Postprocessing The _roff_ postprocessors are programs that have the task to translate the _intermediate_ _output_ into actions that are sent to a device. A device can be some piece of hardware such as a printer, or a software file format suitable for graphical or text processing. The _groff_ sys‐ tem provides powerful means that make the programming of such postprocessors an easy task. There is a library function that parses the _intermediate_ _output_ and sends the information ob‐ tained to the device via methods of a class with a common interface for each device. So a _groff_ postprocessor must only redefine the methods of this class. For details, see the ref‐ erence in section “Files” below. ## Example This section presents the _intermediate_ _output_ generated from the same input for three differ‐ ent devices. The input is the sentence _hell_ _world_ fed into _groff_ on the command line. • High-resolution device _ps_ shell> **echo "hell world" | groff -Z -T ps** x T ps x res 72000 1 1 x init p1 x font 5 TR f5 s10000 V12000 H72000 thell wh2500 tw H96620 torld n12000 0 x trailer V792000 x stop This output can be fed into the postprocessor [_grops_(1)](https://www.chedong.com/phpMan.php/man/grops/1/markdown) to get its representation as a Post‐ Script file, or [_gropdf_(1)](https://www.chedong.com/phpMan.php/man/gropdf/1/markdown) to output directly to PDF. • Low-resolution device _latin1_ This is similar to the high-resolution device except that the positioning is done at a mi‐ nor scale. Some comments (lines starting with _#_) were added for clarification; they were not generated by the formatter. **shell> **"hell world" | groff -Z -T latin1 _#_ _prologue_ x T latin1 x res 240 24 40 x init _#_ _begin_ _a_ _new_ _page_ p1 _#_ _font_ _setup_ x font 1 R f1 s10 _#_ _initial_ _positioning_ _on_ _the_ _page_ V40 H0 _#_ _write_ _text_ _'hell'_ thell _#_ _inform_ _about_ _a_ _space,_ _and_ _do_ _it_ _by_ _a_ _horizontal_ _jump_ wh24 _#_ _write_ _text_ _'world'_ tworld _#_ _announce_ _line_ _break,_ _but_ _do_ _nothing_ _because_ _..._ n40 0 _#_ _..._ _the_ _end_ _of_ _the_ _document_ _has_ _been_ _reached_ x trailer V2640 x stop This output can be fed into the postprocessor [_grotty_(1)](https://www.chedong.com/phpMan.php/man/grotty/1/markdown) to get a formatted text document. • Classical style output As a computer monitor has a very low resolution compared to modern printers the _intermedi‐_ _ate_ _output_ for the X devices can use the jump-and-write command with its 2-digit displace‐ ments. **shell> **"hell world" | groff -Z -T X100 x T X100 x res 100 1 1 x init p1 x font 5 TR f5 s10 V16 H100 _#_ _write_ _text_ _with_ _old-style_ _jump-and-write_ _command_ ch07e07l03lw06w11o07r05l03dh7 n16 0 x trailer V1100 x stop This output can be fed into the postprocessor [_xditview_(1x)](https://www.chedong.com/phpMan.php/man/xditview/1x/markdown) or [_gxditview_(1)](https://www.chedong.com/phpMan.php/man/gxditview/1/markdown) for displaying in X. Due to the obsolete jump-and-write command, the text clusters in the classical output are al‐ most unreadable. ## Compatibility The _intermediate_ _output_ language of the _classical_ _troff_ was first documented in [CSTR #97]. The _groff_ _intermediate_ _output_ format is compatible with this specification except for the following features. • The classical quasi device independence is not yet implemented. • The old hardware was very different from what we use today. So the _groff_ devices are also fundamentally different from the ones in _classical_ _troff_. For example, the classical Post‐ Script device was called _post_ and had a resolution of 720 units per inch, while _groff_'s _ps_ device has a resolution of 72000 units per inch. Maybe, by implementing some rescaling mechanism similar to the classical quasi device independence, these could be integrated into modern _groff_. • The B-spline command **D~ **is correctly handled by the _intermediate_ _output_ parser, but the drawing routines aren't implemented in some of the postprocessor programs. • The argument of the commands **s **and **x H **has the implicit unit scaled point **z **in _groff_, while _classical_ _troff_ had point (**p**). This isn't an incompatibility, but a compatible extension, for both units coincide for all devices without a _sizescale_ parameter, including all clas‐ sical and the _groff_ text devices. The few _groff_ devices with a sizescale parameter either did not exist, had a different name, or seem to have had a different resolution. So con‐ flicts with classical devices are very unlikely. • The position changing after the commands **Dp**, **DP**, and **Dt **is illogical, but as old versions of groff used this feature it is kept for compatibility reasons. The differences between _groff_ and _classical_ _troff_ are documented in [_groff_diff_(7)](https://www.chedong.com/phpMan.php/man/groffdiff/7/markdown). ## Files _/usr/share/groff/1.23.0/font/dev_name_/DESC_ describes the output device _name_. ## Authors James Clark wrote an early version of this document, which described only the differences be‐ tween AT&T device-independent _troff_'s output format and that of GNU _roff_. The present ver‐ sion was completely rewritten in 2001 by [Bernd Warken](mailto:). **See also** _Groff:_ _The_ _GNU_ _Implementation_ _of_ _troff_, by Trent A. Fisher and Werner Lemberg, is the primary _groff_ manual. You can browse it interactively with “info groff”. “Troff User's Manual” by Joseph F. Ossanna, 1976 (revised by Brian W. Kernighan, 1992), AT&T Bell Laboratories Computing Science Technical Report No. 54, widely called simply “CSTR #54”, documents the language, device and font description file formats, and device-independent out‐ put format referred to collectively in _groff_ documentation as “AT&T _troff_”. “A Typesetter-independent TROFF” by Brian W. Kernighan, 1982, AT&T Bell Laboratories Comput‐ ing Science Technical Report No. 97, provides additional insights into the device and font description file formats and device-independent output format. [_groff_(1)](https://www.chedong.com/phpMan.php/man/groff/1/markdown) documents the **-Z **option and contains pointers to further _groff_ documentation. [_groff_(7)](https://www.chedong.com/phpMan.php/man/groff/7/markdown) describes the _groff_ language, including its escape sequences and system of units. [_groff_font_(5)](https://www.chedong.com/phpMan.php/man/grofffont/5/markdown) details the device scaling parameters of device _DESC_ files. [_troff_(1)](https://www.chedong.com/phpMan.php/man/troff/1/markdown) generates the device-independent intermediate output documented here. [_roff_(7)](https://www.chedong.com/phpMan.php/man/roff/7/markdown) presents historical aspects and the general structure of _roff_ systems. [_groff_diff_(7)](https://www.chedong.com/phpMan.php/man/groffdiff/7/markdown) enumerates differences between the intermediate output produced by AT&T _troff_ and that of _groff_. [_gxditview_(1)](https://www.chedong.com/phpMan.php/man/gxditview/1/markdown) is a viewer for intermediate output. _Roff.js_ ⟨⟩ is a viewer for intermediate output written in JavaScript. [_grodvi_(1)](https://www.chedong.com/phpMan.php/man/grodvi/1/markdown), [_grohtml_(1)](https://www.chedong.com/phpMan.php/man/grohtml/1/markdown), [_grolbp_(1)](https://www.chedong.com/phpMan.php/man/grolbp/1/markdown), [_grolj4_(1)](https://www.chedong.com/phpMan.php/man/grolj4/1/markdown), [_gropdf_(1)](https://www.chedong.com/phpMan.php/man/gropdf/1/markdown), [_grops_(1)](https://www.chedong.com/phpMan.php/man/grops/1/markdown), and [_grotty_(1)](https://www.chedong.com/phpMan.php/man/grotty/1/markdown) are _groff_ postprocessors. groff 1.23.0 31 March 2024 [_groff_out_(5)](https://www.chedong.com/phpMan.php/man/groffout/5/markdown)