1GROFF_OUT(5) File Formats Manual GROFF_OUT(5)
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6 groff_out - groff intermediate output format
7
9 This manual page describes the intermediate output format of the GNU
10 roff(7) text processing system groff(1). This output is produced by a
11 run of the GNU troff(1) program. It contains already all device-spe‐
12 cific information, but it is not yet fed into a device postprocessor
13 program.
14 As the GNU roff processor groff(1) is a wrapper program around troff
16 that automatically calls a postprocessor, this output does not show up
17 normally. This is why it is called intermediate within the groff sys‐
18 tem. The groff program provides the option -Z to inhibit postprocess‐
19 ing, such that the produced intermediate output is sent to standard
20 output just like calling troff manually.
21 In this document, the term troff output describes what is output by the
23 GNU troff program, while intermediate output refers to the language
24 that is accepted by the parser that prepares this output for the post‐
25 processors. This parser is smarter on whitespace and implements obso‐
26 lete elements for compatibility, otherwise both formats are the same.
27 Both formats can be viewed directly with gxditview(1).
28 The main purpose of the intermediate output concept is to facilitate
30 the development of postprocessors by providing a common programming in‐
31 terface for all devices. It has a language of its own that is com‐
32 pletely different from the groff(7) language. While the groff language
33 is a high-level programming language for text processing, the interme‐
34 diate output language is a kind of low-level assembler language by
35 specifying all positions on the page for writing and drawing.
36 The pre-groff roff versions are denoted as classical troff. The inter‐
38 mediate output produced by groff is fairly readable, while classical
39 troff output was hard to understand because of strange habits that are
40 still supported, but not used any longer by GNU troff.
41
43 During the run of troff, the roff input is cracked down to the informa‐
44 tion on what has to be printed at what position on the intended device.
45 So the language of the intermediate output format can be quite small.
46 Its only elements are commands with or without arguments. In this doc‐
47 ument, the term “command” always refers to the intermediate output lan‐
48 guage, never to the roff language used for document formatting. There
49 are commands for positioning and text writing, for drawing, and for de‐
50 vice controlling.
51 Separation
53 Classical troff output had strange requirements on whitespace. The
54 groff output parser, however, is smart about whitespace by making it
55 maximally optional. The whitespace characters, i.e., the tab, space,
56 and newline characters, always have a syntactical meaning. They are
57 never printable because spacing within the output is always done by po‐
58 sitioning commands.
59 Any sequence of space or tab characters is treated as a single syntac‐
61 tical space. It separates commands and arguments, but is only required
62 when there would occur a clashing between the command code and the ar‐
63 guments without the space. Most often, this happens when variable
64 length command names, arguments, argument lists, or command clusters
65 meet. Commands and arguments with a known, fixed length need not be
66 separated by syntactical space.
67 A line break is a syntactical element, too. Every command argument can
69 be followed by whitespace, a comment, or a newline character. Thus a
70 syntactical line break is defined to consist of optional syntactical
71 space that is optionally followed by a comment, and a newline charac‐
72 ter.
73 The normal commands, those for positioning and text, consist of a sin‐
75 gle letter taking a fixed number of arguments. For historical reasons,
76 the parser allows stacking of such commands on the same line, but for‐
77 tunately, in groff intermediate output, every command with at least one
78 argument is followed by a line break, thus providing excellent read‐
79 ability.
80 The other commands — those for drawing and device controlling — have a
82 more complicated structure; some recognize long command names, and some
83 take a variable number of arguments. So all D and x commands were de‐
84 signed to request a syntactical line break after their last argument.
85 Only one command, ‘x X’ has an argument that can stretch over several
86 lines, all other commands must have all of their arguments on the same
87 line as the command, i.e., the arguments may not be split by a line
88 break.
89 Empty lines, i.e., lines containing only space and/or a comment, can
91 occur everywhere. They are just ignored.
92 Argument Units
94 Some commands take integer arguments that are assumed to represent val‐
95 ues in a measurement unit, but the letter for the corresponding scale
96 indicator is not written with the output command arguments; see
97 groff(7) and Groff: The GNU Implementation of troff, the groff Texinfo
98 manual, for more on this topic. Most commands assume the scale indica‐
99 tor u, the basic unit of the device, some use z, the scaled point unit
100 of the device, while others, such as the color commands expect plain
101 integers. Note that these scale indicators are relative to the chosen
102 device. They are defined by the parameters specified in the device's
103 DESC file; see groff_font(5).
104 Note that single characters can have the eighth bit set, as can the
106 names of fonts and special characters (this is, glyphs). The names of
107 glyphs and fonts can be of arbitrary length. A glyph that is to be
108 printed will always be in the current font.
109 A string argument is always terminated by the next whitespace character
111 (space, tab, or newline); an embedded # character is regarded as part
112 of the argument, not as the beginning of a comment command. An integer
113 argument is already terminated by the next non-digit character, which
114 then is regarded as the first character of the next argument or com‐
115 mand.
116 Document Parts
118 A correct intermediate output document consists of two parts, the pro‐
119 logue and the body.
120 The task of the prologue is to set the general device parameters using
122 three exactly specified commands. The groff prologue is guaranteed to
123 consist of the following three lines (in that order):
124 x T device
126 x res n h v
127 x init
128 with the arguments set as outlined in subsection “Device Control Com‐
130 mands” below. However, the parser for the intermediate output format
131 is able to swallow additional whitespace and comments as well.
132 The body is the main section for processing the document data. Syntac‐
134 tically, it is a sequence of any commands different from the ones used
135 in the prologue. Processing is terminated as soon as the first x stop
136 command is encountered; the last line of any groff intermediate output
137 always contains such a command.
138 Semantically, the body is page oriented. A new page is started by a
140 p command. Positioning, writing, and drawing commands are always done
141 within the current page, so they cannot occur before the first p com‐
142 mand. Absolute positioning (by the H and V commands) is done relative
143 to the current page, all other positioning is done relative to the cur‐
144 rent location within this page.
145
147 This section describes all intermediate output commands, the classical
148 commands as well as the groff extensions.
149 Comment Command
151 #anything⟨end-of-line⟩
152 A comment. Ignore any characters from the # character up to the
153 next newline character.
154 This command is the only possibility for commenting in the intermediate
156 output. Each comment can be preceded by arbitrary syntactical space;
157 every command can be terminated by a comment.
158 Simple Commands
160 The commands in this subsection have a command code consisting of a
161 single character, taking a fixed number of arguments. Most of them are
162 commands for positioning and text writing. These commands are smart
163 about whitespace. Optionally, syntactical space can be inserted be‐
164 fore, after, and between the command letter and its arguments. All of
165 these commands are stackable, i.e., they can be preceded by other sim‐
166 ple commands or followed by arbitrary other commands on the same line.
167 A separating syntactical space is only necessary when two integer argu‐
168 ments would clash or if the preceding argument ends with a string argu‐
169 ment.
170 C xxx⟨white-space⟩
172 Print a glyph (special character) named xxx. The trailing syn‐
173 tactical space or line break is necessary to allow glyph names
174 of arbitrary length. The glyph is printed at the current print
175 position; the glyph's size is read from the font file. The
176 print position is not changed.
177 c c Print glyph with single-letter name c at the current print posi‐
179 tion; the glyph's size is read from the font file. The print
180 position is not changed.
181 f n Set font to font number n (a non-negative integer).
183 H n Move right to the absolute vertical position n (a non-negative
185 integer in basic units u) relative to left edge of current page.
186 h n Move n (a non-negative integer) basic units u horizontally to
188 the right. [CSTR #54] allows negative values for n also, but
189 groff doesn't use this.
190 m color-scheme [component ...]
192 Set the color for text (glyphs), line drawing, and the outline
193 of graphic objects using different color schemes; the analogous
194 command for the filling color of graphic objects is DF. The
195 color components are specified as integer arguments between 0
196 and 65536. The number of color components and their meaning
197 vary for the different color schemes. These commands are gener‐
198 ated by the groff escape sequence \m. No position changing.
199 These commands are a groff extension.
200 mc cyan magenta yellow
202 Set color using the CMY color scheme, having the 3 color
203 components cyan, magenta, and yellow.
204 md Set color to the default color value (black in most
206 cases). No component arguments.
207 mg gray
209 Set color to the shade of gray given by the argument, an
210 integer between 0 (black) and 65536 (white).
211 mk cyan magenta yellow black
213 Set color using the CMYK color scheme, having the 4 color
214 components cyan, magenta, yellow, and black.
215 mr red green blue
217 Set color using the RGB color scheme, having the 3 color
218 components red, green, and blue.
219 N n Print glyph with index n (an integer, normally non-negative) of
221 the current font. The print position is not changed. If
222 -T html or -T xhtml is used, negative values are emitted also to
223 indicate an unbreakable space with given width. For example,
224 N -193 represents an unbreakable space which has a width of
225 193u. This command is a groff extension.
226 n b a Inform the device about a line break, but no positioning is done
228 by this command. In classical troff, the integer arguments b
229 and a informed about the space before and after the current line
230 to make the intermediate output more human readable without per‐
231 forming any action. In groff, they are just ignored, but they
232 must be provided for compatibility reasons.
233 p n Begin a new page in the outprint. The page number is set to n.
235 This page is completely independent of pages formerly processed
236 even if those have the same page number. The vertical position
237 on the outprint is automatically set to 0. All positioning,
238 writing, and drawing is always done relative to a page, so a
239 p command must be issued before any of these commands.
240 s n Set point size to n scaled points (this is unit z in GNU troff).
242 Classical troff used the unit points (p) instead; see section
243 “Compatibility” below.
244 t xyz...⟨white-space⟩
246 t xyz... dummy-arg⟨white-space⟩
247 Print a word, i.e., a sequence of glyphs with single-letter
248 names x, y, z, etc., terminated by a space character or a line
249 break; an optional second integer argument is ignored (this al‐
250 lows the formatter to generate an even number of arguments).
251 The first glyph should be printed at the current position, the
252 current horizontal position should then be increased by the
253 width of the first glyph, and so on for each glyph. The widths
254 of the glyph are read from the font file, scaled for the current
255 point size, and rounded to a multiple of the horizontal resolu‐
256 tion. Special characters (glyphs with names longer than a sin‐
257 gle letter) cannot be printed using this command; use the C com‐
258 mand for those glyphs. This command is a groff extension; it is
259 only used for devices whose DESC file contains the tcommand key‐
260 word; see groff_font(5).
261 u n xyz...⟨white-space⟩
263 Print word with track kerning. This is the same as the t com‐
264 mand except that after printing each glyph, the current horizon‐
265 tal position is increased by the sum of the width of that glyph
266 and n (an integer in basic units u). This command is a groff
267 extension; it is only used for devices whose DESC file contains
268 the tcommand keyword; see groff_font(5).
269 V n Move down to the absolute vertical position n (a non-negative
271 integer in basic units u) relative to upper edge of current
272 page.
273 v n Move n basic units u down (n is a non-negative integer).
275 [CSTR #54] allows negative values for n also, but groff doesn't
276 use this.
277 w Informs about a paddable whitespace to increase readability.
279 The spacing itself must be performed explicitly by a move com‐
280 mand.
281 Graphics Commands
283 Each graphics or drawing command in the intermediate output starts with
284 the letter D followed by one or two characters that specify a subcom‐
285 mand; this is followed by a fixed or variable number of integer argu‐
286 ments that are separated by a single space character. A D command may
287 not be followed by another command on the same line (apart from a com‐
288 ment), so each D command is terminated by a syntactical line break.
289 troff output follows the classical spacing rules (no space between com‐
291 mand and subcommand, all arguments are preceded by a single space char‐
292 acter), but the parser allows optional space between the command let‐
293 ters and makes the space before the first argument optional. As usual,
294 each space can be any sequence of tab and space characters.
295 Some graphics commands can take a variable number of arguments. In
297 this case, they are integers representing a size measured in basic
298 units u. The h arguments stand for horizontal distances where positive
299 means right, negative left. The v arguments stand for vertical dis‐
300 tances where positive means down, negative up. All these distances are
301 offsets relative to the current location.
302 Unless indicated otherwise, each graphics command directly corresponds
304 to a similar groff \D escape sequence; see groff(7).
305 Unknown D commands are assumed to be device-specific. Its arguments
307 are parsed as strings; the whole information is then sent to the post‐
308 processor.
309 In the following command reference, the syntax element ⟨line-break⟩
311 means a syntactical line break as defined in subsection “Separation”
312 above.
313 D~ h1 v1 h2 v2 ... hn vn⟨line-break⟩
315 Draw B-spline from current position to offset (h1, v1), then to
316 offset (h2, v2) if given, etc., up to (hn, vn). This command
317 takes a variable number of argument pairs; the current position
318 is moved to the terminal point of the drawn curve.
319 Da h1 v1 h2 v2⟨line-break⟩
321 Draw arc from current position to (h1, v1)+(h2, v2) with center
322 at (h1, v1); then move the current position to the final point
323 of the arc.
324 DC d⟨line-break⟩
326 DC d dummy-arg⟨line-break⟩
327 Draw a solid circle using the current fill color with diameter d
328 (integer in basic units u) with leftmost point at the current
329 position; then move the current position to the rightmost point
330 of the circle. An optional second integer argument is ignored
331 (this allows the formatter to generate an even number of argu‐
332 ments). This command is a groff extension.
333 Dc d⟨line-break⟩
335 Draw circle line with diameter d (integer in basic units u) with
336 leftmost point at the current position; then move the current
337 position to the rightmost point of the circle.
338 DE h v⟨line-break⟩
340 Draw a solid ellipse in the current fill color with a horizontal
341 diameter of h and a vertical diameter of v (both integers in ba‐
342 sic units u) with the leftmost point at the current position;
343 then move to the rightmost point of the ellipse. This command
344 is a groff extension.
345 De h v⟨line-break⟩
347 Draw an outlined ellipse with a horizontal diameter of h and a
348 vertical diameter of v (both integers in basic units u) with the
349 leftmost point at current position; then move to the rightmost
350 point of the ellipse.
351 DF color-scheme [component ...]⟨line-break⟩
353 Set fill color for solid drawing objects using different color
354 schemes; the analogous command for setting the color of text,
355 line graphics, and the outline of graphic objects is m. The
356 color components are specified as integer arguments between 0
357 and 65536. The number of color components and their meaning
358 vary for the different color schemes. These commands are gener‐
359 ated by the groff escape sequences \D'F ...' and \M (with no
360 other corresponding graphics commands). No position changing.
361 This command is a groff extension.
362 DFc cyan magenta yellow⟨line-break⟩
364 Set fill color for solid drawing objects using the CMY
365 color scheme, having the 3 color components cyan, ma‐
366 genta, and yellow.
367 DFd ⟨line-break⟩
369 Set fill color for solid drawing objects to the default
370 fill color value (black in most cases). No component ar‐
371 guments.
372 DFg gray⟨line-break⟩
374 Set fill color for solid drawing objects to the shade of
375 gray given by the argument, an integer between 0 (black)
376 and 65536 (white).
377 DFk cyan magenta yellow black⟨line-break⟩
379 Set fill color for solid drawing objects using the CMYK
380 color scheme, having the 4 color components cyan, ma‐
381 genta, yellow, and black.
382 DFr red green blue⟨line-break⟩
384 Set fill color for solid drawing objects using the RGB
385 color scheme, having the 3 color components red, green,
386 and blue.
387 Df n⟨line-break⟩
389 The argument n must be an integer in the range -32767 to 32767.
390 0≤n≤1000
392 Set the color for filling solid drawing objects to a
393 shade of gray, where 0 corresponds to solid white, 1000
394 (the default) to solid black, and values in between to
395 intermediate shades of gray; this is obsoleted by command
396 DFg.
397 n<0 or n>1000
399 Set the filling color to the color that is currently be‐
400 ing used for the text and the outline, see command m.
401 For example, the command sequence
402 mg 0 0 65536
404 Df -1
405 sets all colors to blue.
407 No position changing. This command is a groff extension.
409 Dl h v⟨line-break⟩
411 Draw line from current position to offset (h, v) (integers in
412 basic units u); then set current position to the end of the
413 drawn line.
414 Dp h1 v1 h2 v2 ... hn vn⟨line-break⟩
416 Draw a polygon line from current position to offset (h1, v1),
417 from there to offset (h2, v2), etc., up to offset (hn, vn), and
418 from there back to the starting position. For historical rea‐
419 sons, the position is changed by adding the sum of all arguments
420 with odd index to the actual horizontal position and the even
421 ones to the vertical position. Although this doesn't make sense
422 it is kept for compatibility. This command is a groff exten‐
423 sion.
424 DP h1 v1 h2 v2 ... hn vn⟨line-break⟩
426 The same macro as the corresponding Dp command with the same ar‐
427 guments, but draws a solid polygon in the current fill color
428 rather than an outlined polygon. The position is changed in the
429 same way as with Dp. This command is a groff extension.
430 Dt n⟨line-break⟩
432 Set the current line thickness to n (an integer in basic
433 units u) if n>0; if n=0 select the smallest available line
434 thickness; if n<0 set the line thickness proportional to the
435 point size (this is the default before the first Dt command was
436 specified). For historical reasons, the horizontal position is
437 changed by adding the argument to the actual horizontal posi‐
438 tion, while the vertical position is not changed. Although this
439 doesn't make sense it is kept for compatibility. This command
440 is a groff extension.
441 Device Control Commands
443 Each device control command starts with the letter x followed by a
444 space character (optional or arbitrary space/tab in groff) and a sub‐
445 command letter or word; each argument (if any) must be preceded by a
446 syntactical space. All x commands are terminated by a syntactical line
447 break; no device control command can be followed by another command on
448 the same line (except a comment).
449 The subcommand is basically a single letter, but to increase readabil‐
451 ity, it can be written as a word, i.e., an arbitrary sequence of char‐
452 acters terminated by the next tab, space, or newline character. All
453 characters of the subcommand word but the first are simply ignored.
454 For example, troff outputs the initialization command x i as x init and
455 the resolution command x r as x res. But writings like x i_like_groff
456 and x roff_is_groff are accepted as well to mean the same commands.
457 In the following, the syntax element ⟨line-break⟩ means a syntactical
459 line break as defined in subsection “Separation” above.
460 xF name⟨line-break⟩
462 (Filename control command)
463 Use name as the intended name for the current file in error re‐
464 ports. This is useful for remembering the original file name
465 when groff uses an internal piping mechanism. The input file is
466 not changed by this command. This command is a groff extension.
467 xf n s⟨line-break⟩
469 (font control command)
470 Mount font position n (a non-negative integer) with font named s
471 (a text word); see groff_font(5).
472 xH n⟨line-break⟩
474 (Height control command)
475 Set character height to n (a positive integer in scaled
476 points z). Classical troff used the unit points (p) instead;
477 see section “Compatibility” below.
478 xi ⟨line-break⟩
480 (init control command)
481 Initialize device. This is the third command of the prologue.
482 xp ⟨line-break⟩
484 (pause control command)
485 Parsed but ignored. The classical documentation reads pause de‐
486 vice, can be restarted.
487 xr n h v⟨line-break⟩
489 (resolution control command)
490 Resolution is n, while h is the minimal horizontal motion, and v
491 the minimal vertical motion possible with this device; all argu‐
492 ments are positive integers in basic units u per inch. This is
493 the second command of the prologue.
494 xS n⟨line-break⟩
496 (Slant control command)
497 Set slant to n degrees (an integer in basic units u).
498 xs ⟨line-break⟩
500 (stop control command)
501 Terminates the processing of the current file; issued as the
502 last command of any intermediate troff output.
503 xt ⟨line-break⟩
505 (trailer control command)
506 Generate trailer information, if any. In groff, this is actu‐
507 ally just ignored.
508 xT xxx⟨line-break⟩
510 (Typesetter control command)
511 Set name of device to word xxx, a sequence of characters ended
512 by the next whitespace character. The possible device names co‐
513 incide with those from the groff -T option. This is the first
514 command of the prologue.
515 xu n⟨line-break⟩
517 (underline control command)
518 Configure underlining of spaces. If n is 1, start underlining
519 of spaces; if n is 0, stop underlining of spaces. This is
520 needed for the cu request in nroff mode and is ignored other‐
521 wise. This command is a groff extension.
522 xX anything⟨line-break⟩
524 (X-escape control command)
525 Send string anything uninterpreted to the device. If the line
526 following this command starts with a + character this line is
527 interpreted as a continuation line in the following sense. The
528 + is ignored, but a newline character is sent instead to the de‐
529 vice, the rest of the line is sent uninterpreted. The same ap‐
530 plies to all following lines until the first character of a line
531 is not a + character. This command is generated by the groff
532 escape sequence \X. The line-continuing feature is a groff ex‐
533 tension.
534 Obsolete Command
536 In classical troff output, emitting a single glyph was mostly done by a
537 very strange command that combined a horizontal move and the printing
538 of a glyph. It didn't have a command code, but is represented by a
539 3-character argument consisting of exactly 2 digits and a character.
540 ddc Move right dd (exactly two decimal digits) basic units u, then
542 print glyph with single-letter name c.
543 In groff, arbitrary syntactical space around and within this
545 command is allowed to be added. Only when a preceding command
546 on the same line ends with an argument of variable length a sep‐
547 arating space is obligatory. In classical troff, large clusters
548 of these and other commands were used, mostly without spaces;
549 this made such output almost unreadable.
550 For modern high-resolution devices, this command does not make sense
552 because the width of the glyphs can become much larger than two decimal
553 digits. In groff, this is only used for the devices X75, X75-12, X100,
554 and X100-12. For other devices, the commands t and u provide a better
555 functionality.
556
558 The roff postprocessors are programs that have the task to translate
559 the intermediate output into actions that are sent to a device. A de‐
560 vice can be some piece of hardware such as a printer, or a software
561 file format suitable for graphical or text processing. The groff sys‐
562 tem provides powerful means that make the programming of such postpro‐
563 cessors an easy task.
564 There is a library function that parses the intermediate output and
566 sends the information obtained to the device via methods of a class
567 with a common interface for each device. So a groff postprocessor must
568 only redefine the methods of this class. For details, see the refer‐
569 ence in section “Files” below.
570
572 This section presents the intermediate output generated from the same
573 input for three different devices. The input is the sentence hell
574 world fed into groff on the command line.
575 • High-resolution device ps
577 shell> echo "hell world" | groff -Z -T ps
579 x T ps
581 x res 72000 1 1
582 x init
583 p1
584 x font 5 TR
585 f5
586 s10000
587 V12000
588 H72000
589 thell
590 wh2500
591 tw
592 H96620
593 torld
594 n12000 0
595 x trailer
596 V792000
597 x stop
598 This output can be fed into the postprocessor grops(1) to get its rep‐
600 resentation as a PostScript file, or gropdf(1) to output directly to
601 PDF.
602 • Low-resolution device latin1
604 This is similar to the high-resolution device except that the posi‐
606 tioning is done at a minor scale. Some comments (lines starting with
607 #) were added for clarification; they were not generated by the for‐
608 matter.
609 shell> "hell world" | groff -Z -T latin1
611 # prologue
613 x T latin1
614 x res 240 24 40
615 x init
616 # begin a new page
617 p1
618 # font setup
619 x font 1 R
620 f1
621 s10
622 # initial positioning on the page
623 V40
624 H0
625 # write text ‘hell’
626 thell
627 # inform about a space, and do it by a horizontal jump
628 wh24
629 # write text ‘world’
630 tworld
631 # announce line break, but do nothing because ...
632 n40 0
633 # ... the end of the document has been reached
634 x trailer
635 V2640
636 x stop
637 This output can be fed into the postprocessor grotty(1) to get a for‐
639 matted text document.
640 • Classical style output
642 As a computer monitor has a very low resolution compared to modern
644 printers the intermediate output for the X devices can use the jump-
645 and-write command with its 2-digit displacements.
646 shell> "hell world" | groff -Z -T X100
648 x T X100
650 x res 100 1 1
651 x init
652 p1
653 x font 5 TR
654 f5
655 s10
656 V16
657 H100
658 # write text with old-style jump-and-write command
659 ch07e07l03lw06w11o07r05l03dh7
660 n16 0
661 x trailer
662 V1100
663 x stop
664 This output can be fed into the postprocessor xditview(1x) or
666 gxditview(1) for displaying in X.
667 Due to the obsolete jump-and-write command, the text clusters in the
669 classical output are almost unreadable.
670
672 The intermediate output language of the classical troff was first docu‐
673 mented in [CSTR #97] . The groff intermediate output format is compat‐
674 ible with this specification except for the following features.
675 • The classical quasi device independence is not yet implemented.
677 • The old hardware was very different from what we use today. So the
679 groff devices are also fundamentally different from the ones in clas‐
680 sical troff. For example, the classical PostScript device was called
681 post and had a resolution of 720 units per inch, while groff's ps de‐
682 vice has a resolution of 72000 units per inch. Maybe, by implement‐
683 ing some rescaling mechanism similar to the classical quasi device
684 independence, these could be integrated into modern groff.
685 • The B-spline command D~ is correctly handled by the intermediate out‐
687 put parser, but the drawing routines aren't implemented in some of
688 the postprocessor programs.
689 • The argument of the commands s and x H has the implicit unit scaled
691 point z in groff, while classical troff had point (p). This isn't an
692 incompatibility, but a compatible extension, for both units coincide
693 for all devices without a sizescale parameter, including all classi‐
694 cal and the groff text devices. The few groff devices with a
695 sizescale parameter either did not exist, had a different name, or
696 seem to have had a different resolution. So conflicts with classical
697 devices are very unlikely.
698 • The position changing after the commands Dp, DP, and Dt is illogical,
700 but as old versions of groff used this feature it is kept for compat‐
701 ibility reasons.
702 The differences between groff and classical troff are documented in
704 groff_diff(7).
705
707 /usr/share/groff/1.22.4/font/devname/DESC
708 Device description file for device name.
709 src/libs/libdriver/input.cpp
711 Defines the parser and postprocessor for the intermediate out‐
712 put. It is located relative to the top directory of the groff
713 source tree. This parser is the definitive specification of the
714 groff intermediate output format.
715
717 James Clark wrote an early version of this document, which described
718 only the differences between ditroff(7)'s output format and that of GNU
719 roff. The present version was completely rewritten in 2001 by Bernd
720 Warken ⟨groff-bernd.warken-72@web.de⟩.
721
723 A reference like groff(7) refers to a manual page; here groff in sec‐
724 tion 7 of the man page documentation system. To read the example, look
725 up section 7 in your desktop help system or call from the shell prompt
726 shell> man 7 groff
728 For more details, see man(1).
730 groff(1)
732 option -Z and further readings on groff.
733 groff(7)
735 for details of the groff language such as numerical units and
736 escape sequences.
737 groff_font(5)
739 for details on the device scaling parameters of the DESC file.
740 troff(1)
742 generates the device-independent intermediate output.
743 roff(7)
745 for historical aspects and the general structure of roff sys‐
746 tems.
747 groff_diff(7)
749 The differences between the intermediate output in groff and
750 classical troff.
751 gxditview(1)
753 Viewer for the intermediate output.
754 grodvi(1), grohtml(1), grolbp(1), grolj4(1), grops(1), grotty(1)
756 the groff postprocessor programs.
757 Groff: The GNU Implementation of troff, by Trent A. Fisher and Werner
759 Lemberg, is the primary groff manual. You can browse it interactively
760 with “info groff”.
761 The classical troff output language is described in two AT&T Bell Labs
763 CSTR documents available on-line at Bell Labs CSTR site ⟨http://
764 cm.bell-labs.com/cm/cs/cstr.html⟩.
765 [CSTR #97]
767 A Typesetter-independent TROFF by Brian Kernighan is the origi‐
768 nal and most comprehensive documentation on the output language;
769 see CSTR #97 ⟨http://cm.bell-labs.com/cm/cs/cstr/97.ps.gz⟩.
770 [CSTR #54]
772 The 1992 revision of the Nroff/Troff User's Manual by J. F. Os‐
773 sanna and Brian Kernighan isn't as comprehensive as [CSTR #97]
774 regarding the output language; see CSTR #54 ⟨http://
775 cm.bell-labs.com/cm/cs/cstr/54.ps.gz⟩.
776groff 1.22.4 19 January 2023 GROFF_OUT(5)