This is groff.info, produced by makeinfo version 7.0.3 from groff.texi. This manual documents GNU 'troff' version 1.23.0. Copyright © 1994-2023 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". INFO-DIR-SECTION Typesetting START-INFO-DIR-ENTRY * Groff: (groff). The GNU roff document formatting system. END-INFO-DIR-ENTRY  File: groff.info, Node: Selecting Fonts, Next: Font Families, Prev: Using Fonts, Up: Using Fonts 5.19.1 Selecting Fonts ---------------------- We use "font" to refer to any of several means of identifying a font: by mounting position ('3'), by abstract style ('B'), or by its identifier ('TB'). -- Request: .ft [font] -- Escape sequence: \ff -- Escape sequence: \f(fn -- Escape sequence: \f[font] -- Register: \n[.fn] The 'ft' request selects the typeface FONT. If the argument is absent or 'P', it selects the previously chosen font. If FONT is a non-negative integer, it is interpreted as mounting position; the font mounted there is selected. If that position refers to an abstract style, it is combined with the default family (see 'fam' and '\F' below) to make a resolved font name. If the mounting position is not a style and no font is mounted there, GNU 'troff' emits a warning in category 'font' and ignores the request. If FONT matches a style name, it is combined with the current family to make a resolved font name. Otherwise, FONT is assumed to already be a resolved font name. The resolved font name is subject to translation (see request 'ftr' below). Next, the (possibly translated) font name's mounting position is looked up; if not mounted, FONT is sought on the file system as a font description file and, if located, automatically mounted at the next available position (see register '.fp' below). If the font was mounted using an identifier different from its font description file name (see request 'fp' below), that file name is then looked up. If a font description file for the resolved font name is not found, GNU 'troff' emits a warning in category 'font' and ignores the request. The '\f' escape sequence is similar, using one-character name (or mounting position) F, two-character name FN, or a name FONT of arbitrary length. '\f[]' selects the previous font. The syntax form '\fP' is supported for backward compatibility, and '\f[P]' for consistency. eggs, bacon, .ft I spam, .ft and sausage. .br eggs, bacon, \fIspam,\fP and sausage. => eggs, bacon, spam, and sausage => eggs, bacon, spam, and sausage The current and previously selected fonts are properties of the environment (*note Environments::). The read-only string-valued register '.fn' contains the resolved font name of the selected font. '\f' doesn't produce an input token in GNU 'troff'; it thus can be used in requests that expect a single-character argument. We can assign a font to a margin character as follows (*note Miscellaneous::). .mc \f[I]x\f[] -- Request: .ftr f [g] Translate font F to font G. Whenever a font named F is referred to in a '\f' escape sequence, in the 'F' and 'S' conditional operators, or in the 'ft', 'ul', 'bd', 'cs', 'tkf', 'special', 'fspecial', 'fp', or 'sty' requests, font G is used. If G is missing or equal to F the translation is undone. Font translations cannot be chained. .ftr XXX TR .ftr XXX YYY .ft XXX error-> warning: can't find font 'XXX' -- Request: .fzoom f [zoom] -- Register: \n[.zoom] Set magnification of font F to factor ZOOM, which must be a non-negative integer multiple of 1/1000th. This request is useful to adjust the optical size of a font in relation to the others. In the example below, font 'CR' is magnified by 10% (the zoom factor is thus 1.1). .fam P .fzoom CR 1100 .ps 12 Palatino and \f[CR]Courier\f[] A missing or zero value of ZOOM is the same as a value of 1000, which means no magnification. F must be a resolved font name, not an abstract style. The magnification of a font is completely transparent to GNU 'troff'; a change of the zoom factor doesn't cause any effect except that the dimensions of glyphs, (word) spaces, kerns, etc., of the affected font are adjusted accordingly. The zoom factor of the current font is available in the read-only register '.zoom', in multiples of 1/1000th. It returns zero if there is no magnification.  File: groff.info, Node: Font Families, Next: Font Positions, Prev: Selecting Fonts, Up: Using Fonts 5.19.2 Font Families -------------------- To accommodate the wide variety of fonts available, GNU 'troff' distinguishes "font families" and "font styles". A resolved font name is the catenation of a font family and a style. Selecting an abstract style causes GNU 'troff' to combine it with the default font family. You can thus compose a document using abstract styles exclusively for its body or running text, selecting a specific family only for titles or examples, for instance, and change the default family on the command line (recall *note Groff Options::). Fonts for the devices 'ps', 'pdf', 'dvi', 'lj4', 'lbp', and the X11 devices support this mechanism. By default, GNU 'troff' uses the Times family with the four styles 'R', 'I', 'B', and 'BI'. -- Request: .fam [family] -- Register: \n[.fam] -- Escape sequence: \Ff -- Escape sequence: \F(fm -- Escape sequence: \F[family] Set the default font family, used in combination with abstract styles to construct a resolved font name, to FAMILY (one-character name F, two-character name FM). If no argument is given, GNU 'troff' selects the previous font family; if there none, is it falls back to the device's default(1) (*note Font Families-Footnote-1::) or its own ('T'). The '\F' escape sequence works similarly. In disanalogy to '\f', '\FP' makes 'P' the default family. Use '\F[]' to select the previous default family. The default font family is available in the read-only string-valued register '.fam'; it is associated with the environment (*note Environments::). spam, \" startup defaults are T (Times) R (roman) .fam H \" make Helvetica the default family spam, \" family H + style R = HR .ft B \" family H + style B = HB spam, .ft CR \" Courier roman (default family not changed) spam, .ft \" back to Helvetica bold spam, .fam T \" make Times the default family spam, \" family T + style B = TB .ft AR \" font AR (not a style) baked beans, .ft R \" family T + style R = TR and spam. '\F' doesn't produce an input token in GNU 'troff'. As a consequence, it can be used in requests like 'mc' (which expects a single character as an argument) to change the font family on the fly. .mc \F[P]x\F[] -- Request: .sty n style -- Register: \n[.sty] Associate an abstract style STYLE with mounting position N, which must be a non-negative integer. If the requests 'cs', 'bd', 'tkf', 'uf', or 'fspecial' are applied to an abstract style, they are instead applied to the member of the current family corresponding to that style. The default family can be set with the '-f' option (*note Groff Options::). The 'styles' command in the 'DESC' file controls which font positions (if any) are initially associated with abstract styles rather than fonts. *Caution:* The STYLE argument is not validated. Errors may occur later, when the formatter attempts to construct a resolved font name, or format a character for output. .nr BarPos \n[.fp] .sty \n[.fp] Bar .fam Foo .ft \n[BarPos] .tm .f=\n[.f] A error-> error: no font family named 'Foo' exists error-> .f=41 error-> error: cannot format glyph: no current font When an abstract style has been selected, the read-only string-valued register '.sty' interpolates its name; this datum is associated with the environment (*note Environments::). Otherwise, '.sty' interpolates nothing.  File: groff.info, Node: Font Families-Footnotes, Up: Font Families (1) *Note DESC File Format::.  File: groff.info, Node: Font Positions, Next: Using Symbols, Prev: Font Families, Up: Using Fonts 5.19.3 Font Positions --------------------- To support typeface indirection through abstract styles, and for compatibility with AT&T 'troff', the formatter maintains a list of font "positions" at which fonts required by a document are "mounted". An output device's description file 'DESC' typically configures a set of pre-mounted fonts; see *note Device and Font Description Files::. A font need not be explicitly mounted before it is selected; GNU 'troff' will search 'GROFF_FONT_PATH' for it by name and mount it at the first free mounting position on demand. -- Request: .fp pos id [font-description-file-name] -- Register: \n[.f] -- Register: \n[.fp] Mount a font under the name ID at mounting position POS, a non-negative integer. When the formatter starts up, it reads the output device's description to mount an initial set of faces, and selects font position 1. Position 0 is unused by default. Unless the FONT-DESCRIPTION-FILE-NAME argument is given, ID should be the name of a font description file stored in a directory corresponding to the selected output device. GNU 'troff' does not traverse directories to locate the font description file. The optional third argument enables font names to be aliased, which can be necessary in compatibility mode since AT&T 'troff' syntax affords no means of identifying fonts with names longer than two characters, like 'TBI' or 'ZCMI', in a font selection escape sequence. *Note Compatibility Mode::. You can also alias fonts on mounting for convenience or abstraction. (See below regarding the '.fp' register.) .fp \n[.fp] SC ZCMI Send a \f(SChand-written\fP thank-you note. .fp \n[.fp] Emph TI .fp \n[.fp] Strong TB Are \f[Emph]these names\f[] \f[Strong]comfortable\f[]? 'DESC', 'P', and non-negative integers are not usable as font identifiers. The position of the currently selected font (or abstract style) is available in the read-only register '.f'. It is associated with the environment (*note Environments::). You can copy the value of '.f' to another register to save it for later use. .nr saved-font \n[.f] ... text involving many font changes ... .ft \n[saved-font] The index of the next (non-zero) free font position is available in the read-only register '.fp'. Fonts not listed in the 'DESC' file are automatically mounted at position '\n[.fp]' when selected with the 'ft' request or '\f' escape sequence. When mounting a font at a position explicitly with the 'fp' request, this same practice should be followed, although GNU 'troff' does not enforce this strictly.  File: groff.info, Node: Using Symbols, Next: Character Classes, Prev: Font Positions, Up: Using Fonts 5.19.4 Using Symbols -------------------- A "glyph" is a graphical representation of a "character". While a character is an abstraction of semantic information, a glyph is something that can be seen on screen or paper. A character has many possible representation forms (for example, the character 'A' can be written in an upright or slanted typeface, producing distinct glyphs). Sometimes, a sequence of characters map to a single glyph: this is a "ligature"--the most common is 'fi'. Space characters never become glyphs in GNU 'troff'. If not discarded (as when trailing on text lines), they are represented by horizontal motions in the output. A "symbol" is simply a named glyph. Within 'gtroff', all glyph names of a particular font are defined in its font file. If the user requests a glyph not available in this font, 'gtroff' looks up an ordered list of "special fonts". By default, the PostScript output device supports the two special fonts 'SS' (slanted symbols) and 'S' (symbols) (the former is looked up before the latter). Other output devices use different names for special fonts. Fonts mounted with the 'fonts' keyword in the 'DESC' file are globally available. To install additional special fonts locally (i.e., for a particular font), use the 'fspecial' request. Here are the exact rules how 'gtroff' searches a given symbol: * If the symbol has been defined with the 'char' request, use it. This hides a symbol with the same name in the current font. * Check the current font. * If the symbol has been defined with the 'fchar' request, use it. * Check whether the current font has a font-specific list of special fonts; test all fonts in the order of appearance in the last 'fspecial' call if appropriate. * If the symbol has been defined with the 'fschar' request for the current font, use it. * Check all fonts in the order of appearance in the last 'special' call. * If the symbol has been defined with the 'schar' request, use it. * As a last resort, consult all fonts loaded up to now for special fonts and check them, starting with the lowest font number. This can sometimes lead to surprising results since the 'fonts' line in the 'DESC' file often contains empty positions, which are filled later on. For example, consider the following: fonts 3 0 0 FOO This mounts font 'foo' at font position 3. We assume that 'FOO' is a special font, containing glyph 'foo', and that no font has been loaded yet. The line .fspecial BAR BAZ makes font 'BAZ' special only if font 'BAR' is active. We further assume that 'BAZ' is really a special font, i.e., the font description file contains the 'special' keyword, and that it also contains glyph 'foo' with a special shape fitting to font 'BAR'. After executing 'fspecial', font 'BAR' is loaded at font position 1, and 'BAZ' at position 2. We now switch to a new font 'XXX', trying to access glyph 'foo' that is assumed to be missing. There are neither font-specific special fonts for 'XXX' nor any other fonts made special with the 'special' request, so 'gtroff' starts the search for special fonts in the list of already mounted fonts, with increasing font positions. Consequently, it finds 'BAZ' before 'FOO' even for 'XXX', which is not the intended behaviour. *Note Device and Font Description Files::, and *note Special Fonts::, for more details. The 'groff_char(7)' man page houses a complete list of predefined special character names, but the availability of any as a glyph is device- and font-dependent. For example, say man -Tdvi groff_char > groff_char.dvi to obtain those available with the DVI device and default font configuration.(1) (*note Using Symbols-Footnote-1::) If you want to use an additional macro package to change the fonts used, 'groff' (or 'gtroff') must be run directly. groff -Tdvi -mec -man groff_char.7 > groff_char.dvi Special character names not listed in 'groff_char(7)' are derived algorithmically, using a simplified version of the Adobe Glyph List (AGL) algorithm, which is described in . The (frozen) set of names that can't be derived algorithmically is called the "'groff' glyph list (GGL)". * A glyph for Unicode character U+XXXX[X[X]], which is not a composite character is named 'uXXXX[X[X]]'. X must be an uppercase hexadecimal digit. Examples: 'u1234', 'u008E', 'u12DB8'. The largest Unicode value is 0x10FFFF. There must be at least four 'X' digits; if necessary, add leading zeroes (after the 'u'). No zero padding is allowed for character codes greater than 0xFFFF. Surrogates (i.e., Unicode values greater than 0xFFFF represented with character codes from the surrogate area U+D800-U+DFFF) are not allowed either. * A glyph representing more than a single input character is named 'u' COMPONENT1 '_' COMPONENT2 '_' COMPONENT3 ... Example: 'u0045_0302_0301'. For simplicity, all Unicode characters that are composites must be maximally decomposed to NFD;(2) (*note Using Symbols-Footnote-2::) for example, 'u00CA_0301' is not a valid glyph name since U+00CA (LATIN CAPITAL LETTER E WITH CIRCUMFLEX) can be further decomposed into U+0045 (LATIN CAPITAL LETTER E) and U+0302 (COMBINING CIRCUMFLEX ACCENT). 'u0045_0302_0301' is thus the glyph name for U+1EBE, LATIN CAPITAL LETTER E WITH CIRCUMFLEX AND ACUTE. * groff maintains a table to decompose all algorithmically derived glyph names that are composites itself. For example, 'u0100' (LATIN LETTER A WITH MACRON) is automatically decomposed into 'u0041_0304'. Additionally, a glyph name of the GGL is preferred to an algorithmically derived glyph name; 'groff' also automatically does the mapping. Example: The glyph 'u0045_0302' is mapped to '^E'. * glyph names of the GGL can't be used in composite glyph names; for example, '^E_u0301' is invalid. -- Escape sequence: \(nm -- Escape sequence: \[name] -- Escape sequence: \[base-glyph combining-component ...] Typeset a special character NAME (two-character name NM) or a composite glyph consisting of BASE-GLYPH overlaid with one or more COMBINING-COMPONENTs. For example, '\[A ho]' is a capital letter "A" with a "hook accent" (ogonek). There is no special syntax for one-character names--the analogous form '\N' would collide with other escape sequences. However, the four escape sequences '\'', '\-', '\_', and '\`', are translated on input to the special character escape sequences '\[aa]', '\[-]', '\[ul]', and '\[ga]', respectively. A special character name of length one is not the same thing as an ordinary character: that is, the character 'a' is not the same as '\[a]'. If NAME is undefined, a warning in category 'char' is produced and the escape is ignored. *Note Warnings::, for information about the enablement and suppression of warnings. GNU 'troff' resolves '\[...]' with more than a single component as follows: * Any component that is found in the GGL is converted to the 'uXXXX' form. * Any component 'uXXXX' that is found in the list of decomposable glyphs is decomposed. * The resulting elements are then concatenated with '_' in between, dropping the leading 'u' in all elements but the first. No check for the existence of any component (similar to 'tr' request) is done. Examples: '\[A ho]' 'A' maps to 'u0041', 'ho' maps to 'u02DB', thus the final glyph name would be 'u0041_02DB'. This is not the expected result: the ogonek glyph 'ho' is a spacing ogonek, but for a proper composite a non-spacing ogonek (U+0328) is necessary. Looking into the file 'composite.tmac', one can find '.composite ho u0328', which changes the mapping of 'ho' while a composite glyph name is constructed, causing the final glyph name to be 'u0041_0328'. '\[^E u0301]' '\[^E aa]' '\[E a^ aa]' '\[E ^ ']' '^E' maps to 'u0045_0302', thus the final glyph name is 'u0045_0302_0301' in all forms (assuming proper calls of the 'composite' request). It is not possible to define glyphs with names like 'A ho' within a 'groff' font file. This is not really a limitation; instead, you have to define 'u0041_0328'. -- Escape sequence: \C'xxx' Typeset the glyph of the special character XXX. Normally, it is more convenient to use '\[XXX]', but '\C' has some advantages: it is compatible with AT&T device-independent 'troff' (and therefore available in compatibility mode(3) (*note Using Symbols-Footnote-3::)) and can interpolate special characters with ']' in their names. The delimiter need not be a neutral apostrophe; see *note Delimiters::. -- Request: .composite id1 id2 Map special character name ID1 to ID2 if ID1 is used in '\[...]' with more than one component. See above for examples. This is a strict rewriting of the special character name; no check is performed for the existence of a glyph for either. A set of default mappings for many accents can be found in the file 'composite.tmac', loaded by the default 'troffrc' at startup. -- Escape sequence: \N'n' Typeset the glyph with code N in the current font ('n' is _not_ the input character code). The number N can be any non-negative decimal integer. Most devices only have glyphs with codes between 0 and 255; the Unicode output device uses codes in the range 0-65535. If the current font does not contain a glyph with that code, special fonts are _not_ searched. The '\N' escape sequence can be conveniently used in conjunction with the 'char' request: .char \[phone] \f[ZD]\N'37' The code of each glyph is given in the fourth column in the font description file after the 'charset' command. It is possible to include unnamed glyphs in the font description file by using a name of '---'; the '\N' escape sequence is the only way to use these. No kerning is applied to glyphs accessed with '\N'. The delimiter need not be a neutral apostrophe; see *note Delimiters::. A few escape sequences are also special characters. -- Escape sequence: \' An escaped neutral apostrophe is a synonym for '\[aa]' (acute accent). -- Escape sequence: \` An escaped grave accent is a synonym for '\[ga]' (grave accent). -- Escape sequence: \- An escaped hyphen-minus is a synonym for '\[-]' (minus sign). -- Escape sequence: \_ An escaped underscore ("low line") is a synonym for '\[ul]' (underrule). On typesetting devices, the underrule is font-invariant and drawn lower than the underscore '_'. -- Request: .cflags n c1 c2 ... Assign properties encoded by the number N to characters C1, C2, and so on. Input characters, including special characters introduced by an escape, have certain properties associated with them.(4) (*note Using Symbols-Footnote-4::) These properties can be modified with this request. The first argument is the sum of the desired flags and the remaining arguments are the characters to be assigned those properties. Spaces between the CN arguments are optional. Any argument CN can be a character class defined with the 'class' request rather than an individual character. *Note Character Classes::. The non-negative integer N is the sum of any of the following. Some combinations are nonsensical, such as '33' (1 + 32). '1' Recognize the character as ending a sentence if followed by a newline or two spaces. Initially, characters '.?!' have this property. '2' Enable breaks before the character. A line is not broken at a character with this property unless the characters on each side both have non-zero hyphenation codes. This exception can be overridden by adding 64. Initially, no characters have this property. '4' Enable breaks after the character. A line is not broken at a character with this property unless the characters on each side both have non-zero hyphenation codes. This exception can be overridden by adding 64. Initially, characters '\-\[hy]\[em]' have this property. '8' Mark the glyph associated with this character as overlapping other instances of itself horizontally. Initially, characters '\[ul]\[rn]\[ru]\[radicalex]\[sqrtex]' have this property. '16' Mark the glyph associated with this character as overlapping other instances of itself vertically. Initially, the character '\[br]' has this property. '32' Mark the character as transparent for the purpose of end-of-sentence recognition. In other words, an end-of-sentence character followed by any number of characters with this property is treated as the end of a sentence if followed by a newline or two spaces. This is the same as having a zero space factor in TeX. Initially, characters '"')]*\[dg]\[dd]\[rq]\[cq]' have this property. '64' Ignore hyphenation codes of the surrounding characters. Use this in combination with values 2 and 4 (initially, no characters have this property). For example, if you need an automatic break point after the en-dash in numeric ranges like "3000-5000", insert .cflags 68 \[en] into your document. However, this practice can lead to bad layout if done thoughtlessly; in most situations, a better solution instead of changing the 'cflags' value is to insert '\:' right after the hyphen at the places that really need a break point. The remaining values were implemented for East Asian language support; those who use alphabetic scripts exclusively can disregard them. '128' Prohibit a line break before the character, but allow a line break after the character. This works only in combination with flags 256 and 512 and has no effect otherwise. Initially, no characters have this property. '256' Prohibit a line break after the character, but allow a line break before the character. This works only in combination with flags 128 and 512 and has no effect otherwise. Initially, no characters have this property. '512' Allow line break before or after the character. This works only in combination with flags 128 and 256 and has no effect otherwise. Initially, no characters have this property. In contrast to values 2 and 4, the values 128, 256, and 512 work pairwise. If, for example, the left character has value 512, and the right character 128, no break will be automatically inserted between them. If we use value 6 instead for the left character, a break after the character can't be suppressed since the neighboring character on the right doesn't get examined. -- Request: .char c [contents] -- Request: .fchar c [contents] -- Request: .fschar f c [contents] -- Request: .schar c [contents] Define a new character or glyph C to be CONTENTS, which can be empty. More precisely, 'char' defines a 'groff' object (or redefines an existing one) that is accessed with the name C on input, and produces CONTENTS on output. Every time glyph C needs to be printed, CONTENTS is processed in a temporary environment and the result is wrapped up into a single object. Compatibility mode is turned off and the escape character is set to '\' while CONTENTS is processed. Any emboldening, constant spacing, or track kerning is applied to this object rather than to individual glyphs in CONTENTS. An object defined by these requests can be used just like a normal glyph provided by the output device. In particular, other characters can be translated to it with the 'tr' or 'trin' requests; it can be made the leader character with the 'lc' request; repeated patterns can be drawn with it using the '\l' and '\L' escape sequences; and words containing C can be hyphenated correctly if the 'hcode' request is used to give the object a hyphenation code. There is a special anti-recursion feature: use of the object within its own definition is handled like a normal character (not defined with 'char'). The 'tr' and 'trin' requests take precedence if 'char' accesses the same symbol. .tr XY X => Y .char X Z X => Y .tr XX X => Z The 'fchar' request defines a fallback glyph: 'gtroff' only checks for glyphs defined with 'fchar' if it cannot find the glyph in the current font. 'gtroff' carries out this test before checking special fonts. 'fschar' defines a fallback glyph for font F: 'gtroff' checks for glyphs defined with 'fschar' after the list of fonts declared as font-specific special fonts with the 'fspecial' request, but before the list of fonts declared as global special fonts with the 'special' request. Finally, the 'schar' request defines a global fallback glyph: 'gtroff' checks for glyphs defined with 'schar' after the list of fonts declared as global special fonts with the 'special' request, but before the already mounted special fonts. *Note Character Classes::. -- Request: .rchar c ... -- Request: .rfschar f c ... Remove definition of each ordinary or special character C, undoing the effect of a 'char', 'fchar', or 'schar' request. Those supplied by font description files cannot be removed. Spaces and tabs may separate C arguments. The request 'rfschar' removes glyph definitions defined with 'fschar' for font F.  File: groff.info, Node: Using Symbols-Footnotes, Up: Using Symbols (1) Not all versions of the 'man' program support the '-T' option; use the subsequent example for an alternative. (2) This is "Normalization Form D" as documented in Unicode Standard Annex #15 (). (3) *Note Compatibility Mode::. (4) Output glyphs don't--to GNU 'troff', a glyph is simply a box with an index into a font, a given height above and depth below the baseline, and a width.  File: groff.info, Node: Character Classes, Next: Special Fonts, Prev: Using Symbols, Up: Using Fonts 5.19.5 Character Classes ------------------------ Classes are particularly useful for East Asian languages such as Chinese, Japanese, and Korean, where the number of needed characters is much larger than in European languages, and where large sets of characters share the same properties. -- Request: .class name c1 c2 ... Define a character class (or simply "class") NAME comprising the characters C1, C2, and so on. A class thus defined can then be referred to in lieu of listing all the characters within it. Currently, only the 'cflags' request can handle references to character classes. In the request's simplest form, each CN is a character (or special character). .class [quotes] ' \[aq] \[dq] \[oq] \[cq] \[lq] \[rq] Since class and glyph names share the same name space, it is recommended to start and end the class name with '[' and ']', respectively, to avoid collisions with existing character names defined by GNU 'troff' or the user (with 'char' and related requests). This practice applies the presence of ']' in the class name to prevent the use of the special character escape form '\[...]', thus you must use the '\C' escape to access a class with such a name. You can also use a character range notation consisting of a start character followed by '-' and then an end character. Internally, GNU 'troff' converts these two symbol names to Unicode code points (according to the 'groff' glyph list [GGL]), which then give the start and end value of the range. If that fails, the class definition is skipped. Furthermore, classes can be nested. .class [prepunct] , : ; > } .class [prepunctx] \C'[prepunct]' \[u2013]-\[u2016] The class '[prepunctx]' thus contains the contents of the class '[prepunct]' as defined above (the set ', : ; > }'), and characters in the range between 'U+2013' and 'U+2016'. If you want to include '-' in a class, it must be the first character value in the argument list, otherwise it gets misinterpreted as part of the range syntax. It is not possible to use class names as end points of range definitions. A typical use of the 'class' request is to control line-breaking and hyphenation rules as defined by the 'cflags' request. For example, to inhibit line breaks before the characters belonging to the 'prepunctx' class defined in the previous example, you can write the following. .cflags 2 \C'[prepunctx]' See the 'cflags' request in *note Using Symbols::, for more details.  File: groff.info, Node: Special Fonts, Next: Artificial Fonts, Prev: Character Classes, Up: Using Fonts 5.19.6 Special Fonts -------------------- Special fonts are those that 'gtroff' searches when it cannot find the requested glyph in the current font. The Symbol font is usually a special font. 'gtroff' provides the following two requests to add more special fonts. *Note Using Symbols::, for a detailed description of the glyph searching mechanism in 'gtroff'. Usually, only non-TTY devices have special fonts. -- Request: .special [s1 s2 ...] -- Request: .fspecial f [s1 s2 ...] Use the 'special' request to define special fonts. Initially, this list is empty. Use the 'fspecial' request to designate special fonts only when font F is active. Initially, this list is empty. Previous calls to 'special' or 'fspecial' are overwritten; without arguments, the particular list of special fonts is set to empty. Special fonts are searched in the order they appear as arguments. All fonts that appear in a call to 'special' or 'fspecial' are loaded. *Note Using Symbols::, for the exact search order of glyphs.  File: groff.info, Node: Artificial Fonts, Next: Ligatures and Kerning, Prev: Special Fonts, Up: Using Fonts 5.19.7 Artificial Fonts ----------------------- There are a number of requests and escape sequences for artificially creating fonts. These are largely vestiges of the days when output devices did not have a wide variety of fonts, and when 'nroff' and 'troff' were separate programs. Most of them are no longer necessary in GNU 'troff'. Nevertheless, they are supported. -- Escape sequence: \H'height' -- Escape sequence: \H'+height' -- Escape sequence: \H'-height' -- Register: \n[.height] Change (increment, decrement) the height of the current font, but not the width. If HEIGHT is zero, restore the original height. Default scaling unit is 'z'. The read-only register '.height' contains the font height as set by '\H'. Currently, only the '-Tps' and '-Tpdf' devices support this feature. '\H' doesn't produce an input token in GNU 'troff'. As a consequence, it can be used in requests like 'mc' (which expects a single character as an argument) to change the font on the fly: .mc \H'+5z'x\H'0' In compatibility mode, 'gtroff' behaves differently: If an increment or decrement is used, it is always taken relative to the current type size and not relative to the previously selected font height. Thus, .cp 1 \H'+5'test \H'+5'test prints the word 'test' twice with the same font height (five points larger than the current font size). -- Escape sequence: \S'slant' -- Register: \n[.slant] Slant the current font by SLANT degrees. Positive values slant to the right. Only integer values are possible. The read-only register '.slant' contains the font slant as set by '\S'. Currently, only the '-Tps' and '-Tpdf' devices support this feature. '\S' doesn't produce an input token in GNU 'troff'. As a consequence, it can be used in requests like 'mc' (which expects a single character as an argument) to change the font on the fly: .mc \S'20'x\S'0' This escape is incorrectly documented in the AT&T 'troff' manual; the slant is always set to an absolute value. -- Request: .ul [lines] The 'ul' request normally underlines subsequent lines if a TTY output device is used. Otherwise, the lines are printed in italics (only the term 'underlined' is used in the following). The single argument is the quantity of input lines to be underlined; with no argument, the next line is underlined. If LINES is zero or negative, stop the effects of 'ul' (if it was active). Requests and empty lines do not count for computing the number of underlined input lines, even if they produce some output like 'tl'. Lines inserted by macros (e.g., invoked by a trap) do count. At the beginning of 'ul', the current font is stored and the underline font is activated. Within the span of a 'ul' request, it is possible to change fonts, but after the last line affected by 'ul' the saved font is restored. This number of lines still to be underlined is associated with the environment (*note Environments::). The underline font can be changed with the 'uf' request. The 'ul' request does not underline spaces. -- Request: .cu [lines] The 'cu' request is similar to 'ul' but underlines spaces as well (if a TTY output device is used). -- Request: .uf font Set the underline font (globally) used by 'ul' and 'cu'. By default, this is the font at position 2. FONT can be either a non-negative font position or the name of a font. -- Request: .bd font [offset] -- Request: .bd font1 font2 [offset] -- Register: \n[.b] Embolden FONT by overstriking its glyphs offset by OFFSET units minus one. Two syntax forms are available. * Imitate a bold font unconditionally. The first argument specifies the font to embolden, and the second is the number of basic units, minus one, by which the two glyphs are offset. If the second argument is missing, emboldening is turned off. FONT can be either a non-negative font position or the name of a font. OFFSET is available in the '.b' read-only register if a special font is active; in the 'bd' request, its default unit is 'u'. * Imitate a bold form conditionally. Embolden FONT1 by OFFSET only if font FONT2 is the current font. This request can be issued repeatedly to set up different emboldening values for different current fonts. If the second argument is missing, emboldening is turned off for this particular current font. This affects special fonts only (either set up with the 'special' command in font files or with the 'fspecial' request). -- Request: .cs font [width [em-size]] Switch to and from "constant glyph space mode". If activated, the width of every glyph is WIDTH/36 ems. The em size is given absolutely by EM-SIZE; if this argument is missing, the em value is taken from the current font size (as set with the 'ps' request) when the font is effectively in use. Without second and third argument, constant glyph space mode is deactivated. Default scaling unit for EM-SIZE is 'z'; WIDTH is an integer.  File: groff.info, Node: Ligatures and Kerning, Next: Dummy Characters, Prev: Artificial Fonts, Up: Using Fonts 5.19.8 Ligatures and Kerning ---------------------------- Ligatures are groups of characters that are run together, i.e, producing a single glyph. For example, the letters 'f' and 'i' can form a ligature 'fi' as in the word 'file'. This produces a cleaner look (albeit subtle) to the printed output. Usually, ligatures are not available in fonts for TTY output devices. Most PostScript fonts support the fi and fl ligatures. The C/A/T typesetter that was the target of AT&T 'troff' also supported 'ff', 'ffi', and 'ffl' ligatures. Advanced typesetters or 'expert' fonts may include ligatures for 'ft' and 'ct', although GNU 'troff' does not support these (yet). Only the current font is checked for ligatures and kerns; neither special fonts nor special charcters defined with the 'char' request (and its siblings) are taken into account. -- Request: .lg [flag] -- Register: \n[.lg] Switch the ligature mechanism on or off; if the parameter is non-zero or missing, ligatures are enabled, otherwise disabled. Default is on. The current ligature mode can be found in the read-only register '.lg' (set to 1 or 2 if ligatures are enabled, 0 otherwise). Setting the ligature mode to 2 enables the two-character ligatures (fi, fl, and ff) and disables the three-character ligatures (ffi and ffl). "Pairwise kerning" is another subtle typesetting mechanism that modifies the distance between a glyph pair to improve readability. In most cases (but not always) the distance is decreased. Typewriter-like fonts and fonts for terminals where all glyphs have the same width don't use kerning. -- Request: .kern [flag] -- Register: \n[.kern] Switch kerning on or off. If the parameter is non-zero or missing, enable pairwise kerning, otherwise disable it. The read-only register '.kern' is set to 1 if pairwise kerning is enabled, 0 otherwise. If the font description file contains pairwise kerning information, glyphs from that font are kerned. Kerning between two glyphs can be inhibited by placing '\&' between them: 'V\&A'. *Note Font Description File Format::. "Track kerning" expands or reduces the space between glyphs. This can be handy, for example, if you need to squeeze a long word onto a single line or spread some text to fill a narrow column. It must be used with great care since it is usually considered bad typography if the reader notices the effect. -- Request: .tkf f s1 n1 s2 n2 Enable track kerning for font F. If the current font is F the width of every glyph is increased by an amount between N1 and N2 (N1, N2 can be negative); if the current type size is less than or equal to S1 the width is increased by N1; if it is greater than or equal to S2 the width is increased by N2; if the type size is greater than or equal to S1 and less than or equal to S2 the increase in width is a linear function of the type size. The default scaling unit is 'z' for S1 and S2, 'p' for N1 and N2. The track kerning amount is added even to the rightmost glyph in a line; for large values it is thus recommended to increase the line length by the same amount to compensate.  File: groff.info, Node: Italic Corrections, Next: Dummy Characters, Prev: Ligatures and Kerning, Up: Using Fonts 5.19.9 Italic Corrections ------------------------- When typesetting adjacent glyphs from typefaces of different slants, the space between them may require adjustment. -- Escape sequence: \/ Apply an "italic correction": modify the spacing of the preceding glyph so that the distance between it and the following glyph is correct if the latter is of upright shape. For example, if an italic 'f' is followed immediately by a roman right parenthesis, then in many fonts the top right portion of the 'f' overlaps the top left of the right parenthesis, which is ugly. Use this escape sequence whenever an oblique glyph is immediately followed by an upright glyph without any intervening space. -- Escape sequence: \, Apply a "left italic correction": modify the spacing of the following glyph so that the distance between it and the preceding glyph is correct if the latter is of upright shape. For example, if a roman left parenthesis is immediately followed by an italic 'f', then in many fonts the bottom left portion of the 'f' overlaps the bottom of the left parenthesis, which is ugly. Use this escape sequence whenever an upright glyph is followed immediately by an oblique glyph without any intervening space.  File: groff.info, Node: Dummy Characters, Prev: Italic Corrections, Up: Using Fonts 5.19.10 Dummy Characters ------------------------ As discussed in *note Requests and Macros::, the first character on an input line is treated specially. Further, formatting a glyph has many consequences on formatter state (*note Environments::). Occasionally, we want to escape this context or embrace some of those consequences without actually rendering a glyph to the output. -- Escape sequence: \& Interpolate a dummy character, which is constitutive of output but invisible.(1) (*note Dummy Characters-Footnote-1::) Its presence alters the interpretation context of a subsequent input character, and enjoys several applications. * Prevent insertion of extra space after an end-of-sentence character. Test. Test. => Test. Test. Test.\& Test. => Test. Test. * Prevent recognition of a control character. .Test error-> warning: macro 'Test' not defined \&.Test => .Test * Prevent kerning between two glyphs. * Translate a character to "nothing". .tr JIjiK\&k\&UVuv Post universitum, alea jacta est, OK? => Post vniversitvm, alea iacta est, O? The dummy character escape sequence sees use in macro definitions as a means of ensuring that arguments are treated as text even if they begin with spaces or control characters. .de HD \" typeset a simple bold heading . sp . ft B \&\\$1 \" exercise: remove the \& . ft . sp .. .HD .\|.\|.\|surprised? One way to think about the dummy character is to imagine placing the symbol '&' in the input at a certain location; if doing so has all the side effects on formatting that you desire except for sticking an ugly ampersand in the midst of your text, the dummy character is what you want in its place. -- Escape sequence: \) Interpolate a transparent dummy character--one that is transparent to end-of-sentence detection. It behaves as '\&', except that '\&' is treated as letters and numerals normally are after '.', '?' and '!'; '\&' cancels end-of-sentence detection, and '\)' does not. .de Suffix-& . nop \&\\$1 .. . .de Suffix-) . nop \)\\$1 .. . Here's a sentence.\c .Suffix-& ' Another one.\c .Suffix-) ' And a third. => Here's a sentence.' Another one.' And a third.  File: groff.info, Node: Dummy Characters-Footnotes, Up: Dummy Characters (1) Opinions of this escape sequence's name abound. "Zero-width space" is a popular misnomer: 'roff' formatters do not treat it like a space. Ossanna called it a "non-printing, zero-width character", but the character causes _output_ even though it does not "print". If no output line is pending, the dummy character starts one. Contrast an empty input document with one containing only '\&'. The former produces no output; the latter, a blank page.  File: groff.info, Node: Manipulating Type Size and Vertical Spacing, Next: Colors, Prev: Using Fonts, Up: GNU troff Reference 5.20 Manipulating Type Size and Vertical Spacing ================================================ These concepts were introduced in *note Page Geometry::. The height of a font's tallest glyph is one em, which is equal to the type size in points.(1) (*note Manipulating Type Size and Vertical Spacing-Footnote-1::) A vertical spacing of less than 120% of the type size can make a document hard to read. Larger proportions can be useful to spread the text for annotations or proofreader's marks. By default, GNU 'troff' uses 10 point type on 12 point spacing. Typographers call the difference between type size and vertical spacing "leading".(2) (*note Manipulating Type Size and Vertical Spacing-Footnote-2::) * Menu: * Changing the Type Size:: * Changing the Vertical Spacing:: * Using Fractional Type Sizes::  File: groff.info, Node: Manipulating Type Size and Vertical Spacing-Footnotes, Up: Manipulating Type Size and Vertical Spacing (1) In text fonts, the tallest glyphs are typically parentheses. Unfortunately, in many cases the actual dimensions of the glyphs in a font do not closely match its declared type size! For example, in the standard PostScript font families, 10-point Times sets better with 9-point Helvetica and 11-point Courier than if all three were used at 10 points. (2) Rhyme with "sledding"; mechanical typography used lead metal (Latin _plumbum_).  File: groff.info, Node: Changing the Type Size, Next: Changing the Vertical Spacing, Prev: Manipulating Type Size and Vertical Spacing, Up: Manipulating Type Size and Vertical Spacing 5.20.1 Changing the Type Size ----------------------------- -- Request: .ps [size] -- Request: .ps +size -- Request: .ps -size -- Escape sequence: \ssize -- Register: \n[.s] Use the 'ps' request or the '\s' escape sequence to change (increase, decrease) the type size (in scaled points). Specify SIZE as either an absolute type size, or as a relative change from the current size. 'ps' with no argument restores the previous size. The 'ps' request's default scaling unit is 'z'. The requested size is rounded to the nearest valid size (with ties rounding down) within the limits supported by the device. If the requested size is non-positive, it is treated as 1u. Type size alteration is incorrectly documented in the AT&T 'troff' manual, which claims "if [the requested size] is invalid, the next larger valid size will result, with a maximum of 36".(1) (*note Changing the Type Size-Footnote-1::) The read-only string-valued register '.s' interpolates the type size in points as a decimal fraction; it is associated with the environment (*note Environments::). To obtain the type size in scaled points, interpolate the '.ps' register instead (*note Using Fractional Type Sizes::). The '\s' escape sequence supports a variety of syntax forms. '\sN' Set the type size to N points. N must be a single digit. If N is 0, restore the previous size. '\s+N' '\s-N' Increase or decrease the type size by N points. N must be exactly one digit. '\s(NN' Set the type size to NN points. NN must be exactly two digits. '\s+(NN' '\s-(NN' '\s(+NN' '\s(-NN' Alter the type size in points by the two-digit value NN. *Note Using Fractional Type Sizes::, for further syntactical forms of the '\s' escape sequence that additionally accept decimal fractions. snap, snap, .ps +2 grin, grin, .ps +2 wink, wink, \s+2nudge, nudge,\s+8 say no more! .ps 10 The '\s' escape sequence affects the environment immediately and doesn't produce an input token. Consequently, it can be used in requests like 'mc', which expects a single character as an argument, to change the type size on the fly. .mc \s[20]x\s[0] -- Request: .sizes s1 s2 ... sn [0] The 'DESC' file specifies which type sizes are allowed by the output device; see *note DESC File Format::. Use the 'sizes' request to change this set of permissible sizes. Arguments are in scaled points; see *note Using Fractional Type Sizes::. Each can be a single type size (such as '12000'), or a range of sizes (such as '4000-72000'). You can optionally end the list with a '0'.  File: groff.info, Node: Changing the Type Size-Footnotes, Up: Changing the Type Size (1) The claim appears to have been true of Ossanna 'troff' for the C/A/T device; Kernighan made device-independent 'troff' more flexible.  File: groff.info, Node: Changing the Vertical Spacing, Next: Using Fractional Type Sizes, Prev: Changing the Type Size, Up: Manipulating Type Size and Vertical Spacing 5.20.2 Changing the Vertical Spacing ------------------------------------ -- Request: .vs [space] -- Request: .vs +space -- Request: .vs -space -- Register: \n[.v] Set the vertical spacing to, or alter it by, SPACE. The default scaling unit is 'p'. If 'vs' is called without an argument, the vertical spacing is reset to the previous value before the last call to 'vs'. GNU 'troff' emits a warning in category 'range' if SPACE is negative; the vertical spacing is then set to the smallest possible positive value, the vertical motion quantum (as found in the '.V' register). '.vs 0' isn't saved in a diversion since it doesn't result in a vertical motion. You must explicitly issue this request before interpolating the diversion. The read-only register '.v' contains the vertical spacing; it is associated with the environment (*note Environments::). When a break occurs, GNU 'troff' performs the following procedure. * Move the drawing position vertically by the "extra pre-vertical line space", the minimum of all negative '\x' escape sequence arguments in the pending output line. * Move the drawing position vertically by the vertical line spacing. * Write out the pending output line. * Move the drawing position vertically by the "extra post-vertical line space", the maximum of all positive '\x' escape sequence arguments in the line that has just been output. * Move the drawing position vertically by the "post-vertical line spacing" (see below). Prefer 'vs' or 'pvs' over 'ls' to produce double-spaced documents. 'vs' and 'pvs' have finer granularity than 'ls'; moreover, some preprocessors assume single spacing. *Note Manipulating Spacing::, regarding the '\x' escape sequence and the 'ls' request. -- Request: .pvs [space] -- Request: .pvs +space -- Request: .pvs -space -- Register: \n[.pvs] Set the post-vertical spacing to, or alter it by, SPACE. The default scaling unit is 'p'. If 'pvs' is called without an argument, the post-vertical spacing is reset to the previous value before the last call to 'pvs'. GNU 'troff' emits a warning in category 'range' if SPACE is negative; the post-vertical spacing is then set to zero. The read-only register '.pvs' contains the post-vertical spacing; it is associated with the environment (*note Environments::).  File: groff.info, Node: Using Fractional Type Sizes, Prev: Changing the Type Size, Up: Manipulating Type Size and Vertical Spacing 5.20.3 Using Fractional Type Sizes ---------------------------------- AT&T 'troff' interpreted all type size measurements in points. Combined with integer arithmetic, this design choice made it impossible to support, for instance, ten and a half-point type. In GNU 'troff', an output device can select a scaling factor that subdivides a point into "scaled points". A type size expressed in scaled points can thus represent a non-integral type size. A "scaled point" is equal to 1/SIZESCALE points, where SIZESCALE is specified in the device description file 'DESC', and defaults to 1.(1) (*note Using Fractional Type Sizes-Footnote-1::) Requests and escape sequences in GNU 'troff' interpret arguments that represent a type size in scaled points, which the formatter multiplies by SIZESCALE and converts to an integer. Arguments treated in this way comprise those to the escape sequences '\H' and '\s', to the request 'ps', the third argument to the 'cs' request, and the second and fourth arguments to the 'tkf' request. Scaled points may be specified explicitly with the 'z' scaling unit. For example, if SIZESCALE is 1000, then a scaled point is one thousandth of a point. The request '.ps 10.5' is synonymous with '.ps 10.5z' and sets the type size to 10,500 scaled points, or 10.5 points. Consequently, in GNU 'troff', the register '.s' can interpolate a non-integral type size. -- Register: \n[.ps] This read-only register interpolates the type size in scaled points; it is associated with the environment (*note Environments::). It makes no sense to use the 'z' scaling unit in a numeric expression whose default scaling unit is neither 'u' nor 'z', so GNU 'troff' disallows this. Similarly, it is nonsensical to use a scaling unit other than 'z' or 'u' in a numeric expression whose default scaling unit is 'z', and so GNU 'troff' disallows this as well. Another GNU 'troff' scaling unit, 's', multiplies by the number of basic units in a scaled point. Thus, '\n[.ps]s' is equal to '1m' by definition. Do not confuse the 's' and 'z' scaling units. -- Register: \n[.psr] -- Register: \n[.sr] Output devices may be limited in the type sizes they can employ. The '.s' and '.ps' registers represent the type size selected by the output driver as it understands a device's capability. The last _requested_ type size is interpolated in scaled points by the read-only register '.psr' and in points as a decimal fraction by the read-only string-valued register '.sr'. Both are associated with the environment (*note Environments::). For example, if a type size of 10.95 points is requested, and the nearest size permitted by a 'sizes' request (or by the 'sizes' or 'sizescale' directives in the device's 'DESC' file) is 11 points, the output driver uses the latter value. The '\s' escape sequence offers the following syntax forms that work with fractional type sizes and accept scaling units. You may of course give them integral arguments. The delimited forms need not use the neutral apostrophe; see *note Delimiters::. '\s[N]' '\s'N'' Set the type size to N scaled points; N is a numeric expression with a default scaling unit of 'z'. '\s[+N]' '\s[-N]' '\s+[N]' '\s-[N]' '\s'+N'' '\s'-N'' '\s+'N'' '\s-'N'' Increase or decrease the type size by N scaled points; N is a numeric expression (which may start with a minus sign) with a default scaling unit of 'z'.  File: groff.info, Node: Using Fractional Type Sizes-Footnotes, Up: Using Fractional Type Sizes (1) *Note Device and Font Description Files::.  File: groff.info, Node: Colors, Next: Strings, Prev: Manipulating Type Size and Vertical Spacing, Up: GNU troff Reference 5.21 Colors =========== GNU 'troff' supports color output with a variety of color spaces and up to 16 bits per channel. Some devices, particularly terminals, may be more limited. When color support is enabled, two colors are current at any given time: the "stroke color", with which glyphs, rules (lines), and geometric objects like circles and polygons are drawn, and the "fill color", which can be used to paint the interior of a closed geometric figure. -- Request: .color [n] -- Register: \n[.color] If N is missing or non-zero, enable the output of color-related device-independent output commands (this is the default); otherwise, disable them. This request sets a global flag; it does not produce an input token (*note Gtroff Internals::). The read-only register '.color' is 1 if colors are enabled, 0 otherwise. Color can also be disabled with the '-c' command-line option. -- Request: .defcolor ident scheme color-component ... Define a color named IDENT. SCHEME selects a color space and determines the quantity of required COLOR-COMPONENTs; it must be one of 'rgb' (three components), 'cmy' (three), 'cmyk' (four), or 'gray' (one). 'grey' is accepted as a synonym of 'gray'. The color components can be encoded as a single hexadecimal value starting with '#' or '##'. The former indicates that each component is in the range 0-255 (0-FF), the latter the range 0-65,535 (0-FFFF). .defcolor half gray #7f .defcolor pink rgb #FFC0CB .defcolor magenta rgb ##ffff0000ffff Alternatively, each color component can be specified as a decimal fraction in the range 0-1, interpreted using a default scaling unit of 'f', which multiplies its value by 65,536 (but clamps it at 65,535). .defcolor gray50 rgb 0.5 0.5 0.5 .defcolor darkgreen rgb 0.1f 0.5f 0.2f Each output device has a color named 'default', which cannot be redefined. A device's default stroke and fill colors are not necessarily the same. For the 'dvi', 'html', 'pdf', 'ps', and 'xhtml' output devices, GNU 'troff' automatically loads a macro file defining many color names at startup. By the same mechanism, the devices supported by 'grotty' recognize the eight standard ISO 6429/EMCA-48 color names.(1) (*note Colors-Footnote-1::) -- Request: .gcolor [color] -- Escape sequence: \mc -- Escape sequence: \m(co -- Escape sequence: \m[color] -- Register: \n[.m] Set the stroke color to COLOR. .gcolor red The next words .gcolor \m[red]are in red\m[] and these words are in the previous color. The escape sequence '\m[]' restores the previous stroke color, as does a 'gcolor' request without an argument. The name of the current stroke color is available in the read-only string-valued register '.m'; it is associated with the environment (*note Environments::). It interpolates nothing when the stroke color is the default. '\m' doesn't produce an input token in GNU 'troff' (*note Gtroff Internals::). It therefore can be used in requests like 'mc' (which expects a single character as an argument) to change the color on the fly: .mc \m[red]x\m[] -- Request: .fcolor [color] -- Escape sequence: \Mc -- Escape sequence: \M(co -- Escape sequence: \M[color] -- Register: \n[.M] Set the fill color for objects drawn with '\D'...'' escape sequences. The escape sequence '\M[]' restores the previous fill color, as does an 'fcolor' request without an argument. The name of the current fill color is available in the read-only string-valued register '.M'; it is associated with the environment (*note Environments::). It interpolates nothing when the fill color is the default. '\M' doesn't produce an input token in GNU 'troff'. Create an ellipse with a red interior as follows. \M[red]\h'0.5i'\D'E 2i 1i'\M[]  File: groff.info, Node: Colors-Footnotes, Up: Colors (1) also known vulgarly as "ANSI colors"  File: groff.info, Node: Strings, Next: Conditionals and Loops, Prev: Colors, Up: GNU troff Reference 5.22 Strings ============ GNU 'troff' supports strings primarily for user convenience. Conventionally, if one would define a macro only to interpolate a small amount of text, without invoking requests or calling any other macros, one defines a string instead. Only one string is predefined by the language. -- String: \*[.T] Contains the name of the output device (for example, 'utf8' or 'pdf'). The 'ds' request creates a string with a specified name and contents and the '\*' escape sequence dereferences its name, interpolating its contents. If the string named by the '\*' escape sequence does not exist, it is defined as empty, nothing is interpolated, and a warning in category 'mac' is emitted. *Note Warnings::, for information about the enablement and suppression of warnings. -- Request: .ds name [contents] -- Request: .ds1 name [contents] -- Escape sequence: \*n -- Escape sequence: \*(nm -- Escape sequence: \*[name [arg1 arg2 ...]] Define a string called NAME with contents CONTENTS. If NAME already exists as an alias, the target of the alias is redefined; see 'als' and 'rm' below. If 'ds' is called with only one argument, NAME is defined as an empty string. Otherwise, GNU 'troff' stores CONTENTS in copy mode.(1) (*note Strings-Footnote-1::) The '\*' escape sequence interpolates a previously defined string variable NAME (one-character name N, two-character name NM). The bracketed interpolation form accepts arguments that are handled as macro arguments are; recall *note Calling Macros::. In contrast to macro calls, however, if a closing bracket ']' occurs in a string argument, that argument must be enclosed in double quotes. '\*' is interpreted even in copy mode. When defining strings, argument interpolations must be escaped if they are to reference parameters from the calling context; *Note Parameters::. .ds cite (\\$1, \\$2) Gray codes are explored in \*[cite Morgan 1998]. => Gray codes are explored in (Morgan, 1998). *Caution:* Unlike other requests, the second argument to the 'ds' request consumes the remainder of the input line, including trailing spaces. This means that comments on a line with such a request can introduce unwanted space into a string when they are set off from the material they annotate, as is conventional. .ds H2O H\v'+.3m'\s'-2'2\v'-.3m'\s0O \" water Instead, place the comment on another line or put the comment escape sequence immediately adjacent to the last character of the string. .ds H2O H\v'+.3m'\s'-2'2\v'-.3m'\s0O\" water Ending string definitions (and appendments) with a comment, even an empty one, prevents unwanted space from creeping into them during source document maintenance. .ds author Alice Pleasance Liddell\" .ds empty \" might be appended to later with .as An initial neutral double quote '"' in CONTENTS is stripped to allow embedding of leading spaces. Any other '"' is interpreted literally, but it is wise to use the special character escape sequence '\[dq]' instead if the string might be interpolated as part of a macro argument; see *note Calling Macros::. .ds salutation " Yours in a white wine sauce,\" .ds c-var-defn " char mydate[]=\[dq]2020-07-29\[dq];\" Strings are not limited to a single input line of text. '\' works just as it does elsewhere. The resulting string is stored _without_ the newlines. Care is therefore required when interpolating strings while filling is disabled. .ds foo This string contains \ text on multiple lines \ of input. It is not possible to embed a newline in a string that will be interpreted as such when the string is interpolated. To achieve that effect, use '\*' to interpolate a macro instead; see *note Punning Names::. Because strings are similar to macros, they too can be defined so as to suppress AT&T 'troff' compatibility mode when used; see *note Writing Macros:: and *note Compatibility Mode::. The 'ds1' request defines a string such that compatibility mode is off when the string is later interpolated. To be more precise, a "compatibility save" input token is inserted at the beginning of the string, and a "compatibility restore" input token at the end. .nr xxx 12345 .ds aa The value of xxx is \\n[xxx]. .ds1 bb The value of xxx is \\n[xxx]. . .cp 1 . \*(aa error-> warning: register '[' not defined => The value of xxx is 0xxx]. \*(bb => The value of xxx is 12345. -- Request: .as name [contents] -- Request: .as1 name [contents] The 'as' request is similar to 'ds' but appends CONTENTS to the string stored as NAME instead of redefining it. If NAME doesn't exist yet, it is created. If 'as' is called with only one argument, no operation is performed (beyond dereferencing the string). .as salutation " with shallots, onions and garlic,\" The 'as1' request is similar to 'as', but compatibility mode is switched off when the appended portion of the string is later interpolated. To be more precise, a "compatibility save" input token is inserted at the beginning of the appended string, and a "compatibility restore" input token at the end. Several requests exist to perform rudimentary string operations. Strings can be queried ('length') and modified ('chop', 'substring', 'stringup', 'stringdown'), and their names can be manipulated through renaming, removal, and aliasing ('rn', 'rm', 'als'). -- Request: .length reg anything Compute the number of characters of ANYTHING and store the count in the register REG. If REG doesn't exist, it is created. ANYTHING is read in copy mode. .ds xxx abcd\h'3i'efgh .length yyy \*[xxx] \n[yyy] => 14 -- Request: .chop object Remove the last character from the macro, string, or diversion named OBJECT. This is useful for removing the newline from the end of a diversion that is to be interpolated as a string. This request can be used repeatedly on the same OBJECT; see *note Gtroff Internals::, for details on nodes inserted additionally by GNU 'troff'. -- Request: .substring str start [end] Replace the string named STR with its substring bounded by the indices START and END, inclusively. The first character in the string has index 0. If END is omitted, it is implicitly set to the largest valid value (the string length minus one). Negative indices count backward from the end of the string: the last character has index -1, the character before the last has index -2, and so on. .ds xxx abcdefgh .substring xxx 1 -4 \*[xxx] => bcde .substring xxx 2 \*[xxx] => de -- Request: .stringdown str -- Request: .stringup str Alter the string named STR by replacing each of its bytes with its lowercase ('stringdown') or uppercase ('stringup') version (if one exists). Special characters in the string will often transform in the expected way due to the regular naming convention for accented characters. When they do not, use substrings and/or catenation. .ds resume R\['e]sum\['e] \*[resume] .stringdown resume \*[resume] .stringup resume \*[resume] => Résumé résumé RÉSUMÉ (In practice, we would end the 'ds' request with a comment escape '\"' to prevent space from creeping into the definition during source document maintenance.) -- Request: .rn old new Rename the request, macro, diversion, or string OLD to NEW. -- Request: .rm name Remove the request, macro, diversion, or string NAME. GNU 'troff' treats subsequent invocations as if the name had never been defined. -- Request: .als new old Create an alias NEW for the existing request, string, macro, or diversion object named OLD, causing the names to refer to the same stored object. If OLD is undefined, a warning in category 'mac' is produced, and the request is ignored. *Note Warnings::, for information about the enablement and suppression of warnings. To understand how the 'als' request works, consider two different storage pools: one for objects (macros, strings, etc.), and another for names. As soon as an object is defined, GNU 'troff' adds it to the object pool, adds its name to the name pool, and creates a link between them. When 'als' creates an alias, it adds a new name to the name pool that gets linked to the same object as the old name. Now consider this example. .de foo .. . .als bar foo . .de bar . foo .. . .bar error-> input stack limit exceeded (probable infinite error-> loop) In the above, 'bar' remains an _alias_--another name for--the object referred to by 'foo', which the second 'de' request replaces. Alternatively, imagine that the 'de' request _dereferences_ its argument before replacing it. Either way, the result of calling 'bar' is a recursive loop that finally leads to an error. *Note Writing Macros::. To remove an alias, call 'rm' on its name. The object itself is not destroyed until it has no more names. When a request, macro, string, or diversion is aliased, redefinitions and appendments "write through" alias names. To replace an alias with a separately defined object, you must use the 'rm' request on its name first.  File: groff.info, Node: Strings-Footnotes, Up: Strings (1) *Note Copy Mode::.  File: groff.info, Node: Conditionals and Loops, Next: Writing Macros, Prev: Strings, Up: GNU troff Reference 5.23 Conditionals and Loops =========================== 'groff' has 'if' and 'while' control structures like other languages. However, the syntax for grouping multiple input lines in the branches or bodies of these structures is unusual. * Menu: * Operators in Conditionals:: * if-then:: * if-else:: * Conditional Blocks:: * while::  File: groff.info, Node: Operators in Conditionals, Next: if-then, Prev: Conditionals and Loops, Up: Conditionals and Loops 5.23.1 Operators in Conditionals -------------------------------- In 'if', 'ie', and 'while' requests, in addition to the numeric expressions described in *note Numeric Expressions::, several Boolean operators are available; the members of this expanded class are termed "conditional expressions". 'c GLYPH' True if GLYPH is available, where GLYPH is an ordinary character, a special character '\(XX' or '\[XXX]', '\N'XXX'', or has been defined by any of the 'char', 'fchar', 'fschar', or 'schar' requests. 'd NAME' True if a string, macro, diversion, or request called NAME exists. 'e' True if the current page is even-numbered. 'F FONT' True if FONT exists. FONT is handled as if it were opened with the 'ft' request (that is, font translation and styles are applied), without actually mounting it. 'm COLOR' True if COLOR is defined. 'n' True if the document is being processed in 'nroff' mode. *Note troff and nroff Modes::. 'o' True if the current page is odd-numbered. 'r REGISTER' True if REGISTER exists. 'S STYLE' True if STYLE is available for the current font family. Font translation is applied. 't' True if the document is being processed in 'troff' mode. *Note troff and nroff Modes::. 'v' Always false. This condition is recognized only for compatibility with certain other 'troff' implementations.(1) (*note Operators in Conditionals-Footnote-1::) If the first argument to an 'if', 'ie', or 'while' request begins with a non-alphanumeric character apart from '!' (see below); it performs an output comparison test. (2) (*note Operators in Conditionals-Footnote-2::) ''XXX'YYY'' True if formatting the comparands XXX and YYY produces the same output commands. The delimiter need not be a neutral apostrophe: the output comparison operator accepts the same delimiters as most escape sequences; see *note Delimiters::. This "output comparison operator" formats XXX and YYY in separate environments; after the comparison, the resulting data are discarded. .ie "|"\fR|\fP" true .el false => true The resulting glyph properties, including font family, style, size, and slant, must match, but not necessarily the requests and/or escape sequences used to obtain them. In the previous example, '|' and '\fR|\fP' result in '|' glyphs in the same typefaces at the same positions, so the comparands are equal. If '.ft I' had been added before the '.ie', they would differ: the first '|' would produce an italic '|', not a roman one. Motions must match in orientation and magnitude to within the applicable horizontal and vertical motion quanta of the device, after rounding. '.if "\u\d"\v'0'"' is false even though both comparands result in zero net motion, because motions are not interpreted or optimized but sent as-is to the output.(3) (*note Operators in Conditionals-Footnote-3::) On the other hand, '.if "\d"\v'0.5m'"' is true, because '\d' is defined as a downward motion of one-half em.(4) (*note Operators in Conditionals-Footnote-4::) Surround the comparands with '\?' to avoid formatting them; this causes them to be compared character by character, as with string comparisons in other programming languages. .ie "\?|\?"\?\fR|\fP\?" true .el false => false Since comparands protected with '\?' are read in copy mode (*note Copy Mode::), they need not even be valid 'groff' syntax. The escape character is still lexically recognized, however, and consumes the next character. .ds a \[ .ds b \[ .if '\?\*a\?'\?\*b\?' a and b equivalent .if '\?\\?'\?\\?' backslashes equivalent => a and b equivalent The above operators can't be combined with most others, but a leading '!', not followed immediately by spaces or tabs, complements an expression. .nr x 1 .ie !r x register x is not defined .el register x is defined => register x is defined Spaces and tabs are optional immediately after the 'c', 'd', 'F', 'm', 'r', and 'S' operators, but right after '!', they end the predicate and the conditional evaluates true.(5) (*note Operators in Conditionals-Footnote-5::) .nr x 1 .ie ! r x register x is not defined .el register x is defined => r x register x is not defined The unexpected 'r x' in the output is a clue that our conditional was not interpreted as we planned, but matters may not always be so obvious.  File: groff.info, Node: Operators in Conditionals-Footnotes, Up: Operators in Conditionals (1) This refers to 'vtroff', a translator that would convert the C/A/T output from early-vintage AT&T 'troff' to a form suitable for Versatec and Benson-Varian plotters. (2) Strictly, letters not otherwise recognized _are_ treated as output comparison delimiters. For portability, it is wise to avoid using letters not in the list above; for example, Plan 9 'troff' uses 'h' to test a mode it calls 'htmlroff', and GNU 'troff' may provide additional operators in the future. (3) Because formatting of the comparands takes place in a dummy environment, vertical motions within them cannot spring traps. (4) All of this is to say that the lists of output nodes created by formatting XXX and YYY must be identical. *Note Gtroff Internals::. (5) This bizarre behavior maintains compatibility with AT&T 'troff'.  File: groff.info, Node: if-then, Next: if-else, Prev: Operators in Conditionals, Up: Conditionals and Loops 5.23.2 if-then -------------- -- Request: .if cond-expr anything Evaluate the conditional expression COND-EXPR, and if it evaluates true (or to a positive value), interpret the remainder of the line ANYTHING as if it were an input line. Recall from *note Invoking Requests:: that any quantity of spaces between arguments to requests serves only to separate them; leading spaces in ANYTHING are thus not seen. ANYTHING effectively _cannot_ be omitted; if COND-EXPR is true and ANYTHING is empty, the newline at the end of the control line is interpreted as a blank input line (and therefore a blank text line). super\c tanker .nr force-word-break 1 super\c .if ((\n[force-word-break] = 1) & \n[.int]) tanker => supertanker super tanker -- Request: .nop anything Interpret ANYTHING as if it were an input line. This is similar to '.if 1'. 'nop' is not really "no operation"; its argument _is_ processed--unconditionally. It can be used to cause text lines to share indentation with surrounding control lines. .als real-MAC MAC .de wrapped-MAC . tm MAC: called with arguments \\$@ . nop \\*[real-MAC]\\ .. .als MAC wrapped-MAC \# Later... .als MAC real-MAC In the above, we've used aliasing, 'nop', and the interpolation of a macro as a string to interpose a wrapper around the macro 'MAC' (perhaps to debug it).  File: groff.info, Node: if-else, Next: while, Prev: Operators in Conditionals, Up: Conditionals and Loops 5.23.3 if-else -------------- -- Request: .ie cond-expr anything -- Request: .el anything Use the 'ie' and 'el' requests to write an if-then-else. The first request is the "if" part and the latter is the "else" part. Unusually among programming languages, any number of non-conditional requests may be interposed between the 'ie' branch and the 'el' branch. .nr a 0 .ie \na a is non-zero. .nr a +1 .el a was not positive but is now \na. => a was not positive but is now 1. Another way in which 'el' is an ordinary request is that it does not lexically "bind" more tightly to its 'ie' counterpart than it does to any other request. This fact can surprise C programmers. .nr a 1 .nr z 0 .ie \nz \ . ie \na a is true . el a is false .el z is false error-> warning: unbalanced 'el' request => a is false To conveniently nest conditionals, keep reading.  File: groff.info, Node: Conditional Blocks, Next: while, Prev: Operators in Conditionals, Up: Conditionals and Loops 5.23.4 Conditional Blocks ------------------------- It is frequently desirable for a control structure to govern more than one request, macro call, text line, or a combination of the foregoing. The opening and closing brace escape sequences '\{' and '\}' define such groups. These "conditional blocks" can furthermore be nested. -- Escape sequence: \{ -- Escape sequence: \} '\{' begins a conditional block; it must appear (after optional spaces and tabs) immediately subsequent to the conditional expression of an 'if', 'ie', or 'while' request,(1) (*note Conditional Blocks-Footnote-1::) or as the argument to an 'el' request. '\}' ends a condition block and should appear on a line with other occurrences of itself as necessary to match '\{' sequences. It can be preceded by a control character, spaces, and tabs. Input after any quantity of '\}' sequences on the same line is processed only if all of the preceding conditions to which they correspond are true. Furthermore, a '\}' closing the body of a 'while' request must be the last such escape sequence on an input line. Brace escape sequences outside of control structures have no meaning and produce no output. *Caution:* Input lines using '\{' often end with '\RET', especially in macros that consist primarily of control lines. Forgetting to use '\RET' on an input line after '\{' is a common source of error. We might write the following in a page header macro. If we delete '\RET', the header will carry an unwanted extra empty line (except on page 1). .if (\\n[%] != 1) \{\ . ie ((\\n[%] % 2) = 0) .tl \\*[even-numbered-page-title] . el .tl \\*[odd-numbered-page-title] .\} Let us take a closer look at how conditional blocks nest. A .if 0 \{ B C D \}E F => A F N .if 1 \{ O . if 0 \{ P Q R\} S\} T U => N O U The above behavior may challenge the intuition; it was implemented to retain compatibility with AT&T 'troff'. For clarity, it is idiomatic to end input lines with '\{' (followed by '\' if appropriate), and to precede '\}' on an input line with nothing more than a control character, spaces, tabs, and other instances of itself. We can use 'ie', 'el', and conditional blocks to simulate the multi-way "switch" or "case" control structures of other languages. The following example is adapted from the 'groff' 'man' package. Indentation is used to clarify the logic. .\" Simulate switch/case in roff. . ie '\\$2'1' .ds title General Commands\" .el \{.ie '\\$2'2' .ds title System Calls\" .el \{.ie '\\$2'3' .ds title Library Functions\" .el \{.ie '\\$2'4' .ds title Kernel Interfaces\" .el \{.ie '\\$2'5' .ds title File Formats\" .el \{.ie '\\$2'6' .ds title Games\" .el \{.ie '\\$2'7' .ds title Miscellaneous Information\" .el \{.ie '\\$2'8' .ds title System Management\" .el \{.ie '\\$2'9' .ds title Kernel Development\" .el .ds title \" empty .\}\}\}\}\}\}\}\}  File: groff.info, Node: Conditional Blocks-Footnotes, Up: Conditional Blocks (1) *Note while::.  File: groff.info, Node: while, Prev: if-else, Up: Conditionals and Loops 5.23.5 while ------------ 'groff' provides a looping construct: the 'while' request. Its syntax matches the 'if' request. -- Request: .while cond-expr anything Evaluate the conditional expression COND-EXPR, and repeatedly execute ANYTHING unless and until COND-EXPR evaluates false. ANYTHING, which is often a conditional block, is referred to as the 'while' request's "body". .nr a 0 1 .while (\na < 9) \{\ \n+a, .\} \n+a => 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 GNU 'troff' treats the body of a 'while' request similarly to that of a 'de' request (albeit one not read in copy mode(1) (*note while-Footnote-1::)), but stores it under an internal name and deletes it when the loop finishes. The operation of a macro containing a 'while' request can slow significantly if the 'while' body is large. Each time the macro is executed, the 'while' body is parsed and stored again. .de xxx . nr num 10 . while (\\n[num] > 0) \{\ . \" many lines of code . nr num -1 . \} .. An often better solution--and one that is more portable, since AT&T 'troff' lacked the 'while' request--is to instead write a recursive macro. It will be parsed only once.(2) (*note while-Footnote-2::) .de yyy . if (\\n[num] > 0) \{\ . \" many lines of code . nr num -1 . yyy . \} .. . .de xxx . nr num 10 . yyy .. To prevent infinite loops, the default number of available recursion levels is 1,000 or somewhat less.(3) (*note while-Footnote-3::) You can disable this protective measure, or raise the limit, by setting the 'slimit' register. *Note Debugging::. As noted above, if a 'while' body begins with a conditional block, its closing brace must end an input line. .if 1 \{\ . nr a 0 1 . while (\n[a] < 10) \{\ . nop \n+[a] .\}\} error-> unbalanced brace escape sequences -- Request: .break Exit a 'while' loop. Do not confuse this request with a typographical break or the 'br' request. -- Request: .continue Skip the remainder of a 'while' loop's body, immediately starting the next iteration.  File: groff.info, Node: while-Footnotes, Up: while (1) *Note Copy Mode::. (2) unless you redefine it (3) "somewhat less" because things other than macro calls can be on the input stack  File: groff.info, Node: Writing Macros, Next: Page Motions, Prev: Conditionals and Loops, Up: GNU troff Reference 5.24 Writing Macros =================== A "macro" is a stored collection of text and control lines that can be interpolated multiple times. Use macros to define common operations. Macros are called in the same way that requests are invoked. While requests exist for the purpose of creating macros, simply calling an undefined macro, or interpolating it as a string, will cause it to be defined as empty. *Note Identifiers::. -- Request: .de name [end] Define a macro NAME, replacing the definition of any existing request, macro, string, or diversion called NAME. If NAME already exists as an alias, the target of the alias is redefined; recall *note Strings::. GNU 'troff' enters copy mode,(1) (*note Writing Macros-Footnote-1::) storing subsequent input lines as the macro definition. If the optional second argument is not specified, the definition ends with the control line '..' (two dots). Alternatively, END identifies a macro whose call syntax at the start of a control line ends the definition of NAME; END is then called normally. A macro definition must end in the same conditional block (if any) in which it began (*note Conditional Blocks::). Spaces or tabs are permitted after the control character in the line containing this ending token (either '.' or 'END'), but a tab immediately after the token prevents its recognition as the end of a macro definition. The macro END can be called with arguments.(2) (*note Writing Macros-Footnote-2::) Here is a small example macro called 'P' that causes a break and inserts some vertical space. It could be used to separate paragraphs. .de P . br . sp .8v .. We can define one macro within another. Attempting to nest '..' naïvely will end the outer definition because the inner definition isn't interpreted as such until the outer macro is later interpolated. We can use an end macro instead. Each level of nesting should use a unique end macro. An end macro need not be defined until it is called. This fact enables a nested macro definition to begin inside one macro and end inside another. Consider the following example.(3) (*note Writing Macros-Footnote-3::) .de m1 . de m2 m3 you .. .de m3 Hello, Joe. .. .de m4 do .. .m1 know? . m3 What .m4 .m2 => Hello, Joe. What do you know? A nested macro definition _can_ be terminated with '..' and nested macros _can_ reuse end macros, but these control lines must be escaped multiple times for each level of nesting. The necessity of this escaping and the utility of nested macro definitions will become clearer when we employ macro parameters and consider the behavior of copy mode in detail. 'de' defines a macro that inherits the compatibility mode enablement status of its context (*note Implementation Differences::). Often it is desirable to make a macro that uses 'groff' features callable from contexts where compatibility mode is on; for instance, when writing extensions to a historical macro package. To achieve this, compatibility mode needs to be switched off while such a macro is interpreted--without disturbing that state when it is finished. -- Request: .de1 name [end] The 'de1' request defines a macro to be interpreted with compatibility mode disabled. When NAME is called, compatibility mode enablement status is saved; it is restored when the call completes. Observe the extra backlash before the interpolation of register 'xxx'; we'll explore this subject in *note Copy Mode::. .nr xxx 12345 .de aa The value of xxx is \\n[xxx]. . br .. .de1 bb The value of xxx is \\n[xxx]. .. .cp 1 .aa error-> warning: register '[' not defined => The value of xxx is 0xxx]. .bb => The value of xxx is 12345. -- Request: .dei name [end] -- Request: .dei1 name [end] The 'dei' request defines a macro with its name and end macro indirected through strings. That is, it interpolates strings named NAME and END before performing the definition. The following examples are equivalent. .ds xx aa .ds yy bb .dei xx yy .de aa bb The 'dei1' request bears the same relationship to 'dei' as 'de1' does to 'de'; it temporarily turns compatibility mode off when NAME is called. -- Request: .am name [end] -- Request: .am1 name [end] -- Request: .ami name [end] -- Request: .ami1 name [end] 'am' appends subsequent input lines to macro NAME, extending its definition, and otherwise working as 'de' does. To make the previously defined 'P' macro set indented instead of block paragraphs, add the necessary code to the existing macro. .am P .ti +5n .. The other requests are analogous to their 'de' counterparts. The 'am1' request turns off compatibility mode during interpretation of the appendment. The 'ami' request appends indirectly, meaning that strings NAME and END are interpolated with the resulting names used before appending. The 'ami1' request is similar to 'ami', disabling compatibility mode during interpretation of the appended lines. Using 'trace.tmac', you can trace calls to 'de', 'de1', 'am', and 'am1'. You can also use the 'backtrace' request at any point desired to troubleshoot tricky spots (*note Debugging::). *Note Strings::, for the 'als', 'rm', and 'rn' requests to create an alias of, remove, and rename a macro, respectively. Macro identifiers share their name space with requests, strings, and diversions; see *note Identifiers::. The 'am', 'as', 'da', 'de', 'di', and 'ds' requests (together with their variants) create a new object only if the name of the macro, diversion, or string is currently undefined or if it is defined as a request; normally, they modify the value of an existing object. *Note the description of the 'als' request: als, for pitfalls when redefining a macro that is aliased. -- Request: .return [anything] Exit a macro, immediately returning to the caller. If called with an argument ANYTHING, exit twice--the current macro and the macro one level higher. This is used to define a wrapper macro for 'return' in 'trace.tmac'. * Menu: * Parameters:: * Copy Mode::  File: groff.info, Node: Writing Macros-Footnotes, Up: Writing Macros (1) *Note Copy Mode::. (2) While it is possible to define and call a macro '.', you can't use it as an end macro: during a macro definition, '..' is never handled as calling '.', even if '.de NAME .' explicitly precedes it. (3) Its structure is adapted from, and isomorphic to, part of a solution by Tadziu Hoffman to the problem of reflowing text multiple times to find an optimal configuration for it.  File: groff.info, Node: Parameters, Next: Copy Mode, Prev: Writing Macros, Up: Writing Macros 5.24.1 Parameters ----------------- Macro calls and string interpolations optionally accept a list of arguments; recall *note Calling Macros::. At the time such an interpolation takes place, these "parameters" can be examined using a register and a variety of escape sequences starting with '\$'. All such escape sequences are interpreted even in copy mode, a fact we shall motivate and explain below (*note Copy Mode::). -- Register: \n[.$] The count of parameters available to a macro or string is kept in this read-only register. The 'shift' request can change its value. Any individual parameter can be accessed by its position in the list of arguments to the macro call, numbered from left to right starting at 1, with one of the following escape sequences. -- Escape sequence: \$n -- Escape sequence: \$(nn -- Escape sequence: \$[nnn] Interpolate the Nth, NNth, or NNNth parameter. The first form expects only a single digit (1<=N<=9)), the second two digits (01<=NN<=99)), and the third any positive integer NNN. Macros and strings accept an unlimited number of parameters. -- Request: .shift [n] Shift the parameters N places (1 by default). This is a "left shift": what was parameter I becomes parameter I-N. The parameters formerly in positions 1 to N are no longer available. Shifting by a non-positive amount performs no operation. The register '.$' is adjusted accordingly. In practice, parameter interpolations are usually seen prefixed with an extra escape character. This is because the '\$' family of escape sequences is interpreted even in copy mode.(1) (*note Parameters-Footnote-1::) -- Escape sequence: \$* -- Escape sequence: \$@ -- Escape sequence: \$^ In some cases it is convenient to interpolate all of the parameters at once (to pass them to a request, for instance). The '\$*' escape concatenates the parameters, separating them with spaces. '\$@' is similar, concatenating the parameters, surrounding each with double quotes and separating them with spaces. If not in compatibility mode, the interpolation depth of double quotes is preserved (*note Calling Macros::). '\$^' interpolates all parameters as if they were arguments to the 'ds' request. .de foo . tm $1='\\$1' . tm $2='\\$2' . tm $*='\\$*' . tm $@='\\$@' . tm $^='\\$^' .. .foo " This is a "test" error-> $1=' This is a ' error-> $2='test"' error-> $*=' This is a test"' error-> $@='" This is a " "test""' error-> $^='" This is a "test"' '\$*' is useful when writing a macro that doesn't need to distinguish its arguments, or even to not interpret them; examples include macros that produce diagnostic messages by wrapping the 'tm' or 'ab' requests. Use '\$@' when writing a macro that may need to shift its parameters and/or wrap a macro or request that finds the count significant. If in doubt, prefer '\$@' to '\$*'. An application of '\$^' is seen in 'trace.tmac', which redefines some requests and macros for debugging purposes. -- Escape sequence: \$0 Interpolate the name by which the macro being interpreted was called. The 'als' request can cause a macro to have more than one name. Applying string interpolation to a macro does not change this name. .de foo . tm \\$0 .. .als bar foo . .de aaa . foo .. .de bbb . bar .. .de ccc \\*[foo]\\ .. .de ddd \\*[bar]\\ .. . .aaa error-> foo .bbb error-> bar .ccc error-> ccc .ddd error-> ddd  File: groff.info, Node: Parameters-Footnotes, Up: Parameters (1) If they were not, parameter interpolations would be similar to command-line parameters--fixed for the entire duration of a 'roff' program's run. The advantage of interpolating '\$' escape sequences even in copy mode is that they can interpolate different contents from one call to the next, like function parameters in a procedural language. The additional escape character is the price of this power.  File: groff.info, Node: Copy Mode, Prev: Parameters, Up: Writing Macros 5.24.2 Copy Mode ---------------- When GNU 'troff' processes certain requests, most importantly those which define or append to a macro or string, it does so in "copy mode": it copies the characters of the definition into a dedicated storage region, interpolating the escape sequences '\n', '\g', '\$', '\*', '\V', and '\?' normally; interpreting '\' immediately; discarding comments '\"' and '\#'; interpolating the current leader, escape, or tab character with '\a', '\e', and '\t', respectively; and storing all other escape sequences in an encoded form. The complement of copy mode--a 'roff' formatter's behavior when not defining or appending to a macro, string, or diversion--where all macros are interpolated, requests invoked, and valid escape sequences processed immediately upon recognition, can be termed "interpretation mode". -- Escape sequence: \\ The escape character, '\' by default, can escape itself. This enables you to control whether a given '\n', '\g', '\$', '\*', '\V', or '\?' escape sequence is interpreted at the time the macro containing it is defined, or later when the macro is called.(1) (*note Copy Mode-Footnote-1::) .nr x 20 .de y .nr x 10 \&\nx \&\\nx .. .y => 20 10 You can think of '\\' as a "delayed" backslash; it is the escape character followed by a backslash from which the escape character has removed its special meaning. Consequently, '\\' is not an escape sequence in the usual sense. In any escape sequence '\X' that GNU 'troff' does not recognize, the escape character is ignored and X is output. An unrecognized escape sequence causes a warning in category 'escape', with two exceptions--'\\' is the first. -- Escape sequence: \. '\.' escapes the control character. It is similar to '\\' in that it isn't a true escape sequence. It is used to permit nested macro definitions to end without a named macro call to conclude them. Without a syntax for escaping the control character, this would not be possible. .de m1 foo . . de m2 bar \\.. . .. .m1 .m2 => foo bar The first backslash is consumed while the macro is read, and the second is interpreted when macro 'm1' is called. 'roff' documents should not use the '\\' or '\.' character sequences outside of copy mode; they serve only to obfuscate the input. Use '\e' to represent the escape character, '\[rs]' to obtain a backslash glyph, and '\&' before '.' and ''' where GNU 'troff' expects them as control characters if you mean to use them literally (recall *note Requests and Macros::). Macro definitions can be nested to arbitrary depth. The mechanics of parsing the escape character have significant consequences for this practice. .de M1 \\$1 . de M2 \\\\$1 . de M3 \\\\\\\\$1 \\\\.. . M3 hand. \\.. . M2 of .. This understeer is getting .M1 out => This understeer is getting out of hand. Each escape character is interpreted twice--once in copy mode, when the macro is defined, and once in interpretation mode, when the macro is called. As seen above, this fact leads to exponential growth in the quantity of escape characters required to delay interpolation of '\n', '\g', '\$', '\*', '\V', and '\?' at each nesting level, which can be daunting. GNU 'troff' offers a solution. -- Escape sequence: \E '\E' represents an escape character that is not interpreted in copy mode. You can use it to ease the writing of nested macro definitions. .de M1 . nop \E$1 . de M2 . nop \E$1 . de M3 . nop \E$1 \\\\.. . M3 better. \\.. . M2 bit .. This vehicle handles .M1 a => This vehicle handles a bit better. Observe that because '\.' is not a true escape sequence, we can't use '\E' to keep '..' from ending a macro definition prematurely. If the multiplicity of backslashes complicates maintenance, use end macros. '\E' is also convenient to define strings containing escape sequences that need to work when used in copy mode (for example, as macro arguments), or which will be interpolated at varying macro nesting depths. We might define strings to begin and end superscripting as follows.(2) (*note Copy Mode-Footnote-2::) .ds { \v'-.9m\s'\En[.s]*7u/10u'+.7m' .ds } \v'-.7m\s0+.9m' When the 'ec' request is used to redefine the escape character, '\E' also makes it easier to distinguish the semantics of an escape character from the other meaning(s) its character might have. Consider the use of an unusual escape character, '-'. .nr a 1 .ec - .de xx --na .. .xx => -na This result may surprise you; some people expect '1' to be output since register 'a' has clearly been defined with that value. What has happened? The robotic replacement of '\' with '-' has led us astray. You might recognize the sequence '--' more readily with the default escape character as '\-', the special character escape sequence for the minus sign glyph. .nr a 1 .ec - .de xx -Ena .. .xx => 1  File: groff.info, Node: Copy Mode-Footnotes, Up: Copy Mode (1) Compare this to the '\def' and '\edef' commands in TeX. (2) These are lightly adapted from the 'groff' implementation of the 'ms' macros.  File: groff.info, Node: Page Motions, Next: Drawing Geometric Objects, Prev: Writing Macros, Up: GNU troff Reference 5.25 Page Motions ================= *Note Manipulating Spacing::, for a discussion of the most commonly used request for vertical motion, 'sp', which spaces downward by one vee. -- Request: .mk [reg] -- Request: .rt [dist] You can "mark" a location on a page for subsequent "return". 'mk' takes an argument, a register name in which to store the current page location. If given no argument, it stores the location in an internal register. This location can be used later by the 'rt' or the 'sp' requests (or the '\v' escape). The 'rt' request returns _upward_ to the location marked with the last 'mk' request. If used with an argument, it returns to a vertical position DIST from the top of the page (no previous call to 'mk' is necessary in this case). The default scaling unit is 'v'. If a page break occurs between a 'mk' request and its matching 'rt' request, the 'rt' request is silently ignored. A simple implementation of a macro to set text in two columns follows. .nr column-length 1.5i .nr column-gap 4m .nr bottom-margin 1m . .de 2c . br . mk . ll \\n[column-length]u . wh -\\n[bottom-margin]u 2c-trap . nr right-side 0 .. . .de 2c-trap . ie \\n[right-side] \{\ . nr right-side 0 . po -(\\n[column-length]u + \\n[column-gap]u) . \" remove trap . wh -\\n[bottom-margin]u . \} . el \{\ . \" switch to right side . nr right-side 1 . po +(\\n[column-length]u + \\n[column-gap]u) . rt . \} .. Now let us apply our two-column macro. .pl 1.5i .ll 4i This is a small test that shows how the rt request works in combination with mk. .2c Starting here, text is typeset in two columns. Note that this implementation isn't robust and thus not suited for a real two-column macro. => This is a small test that shows how the => rt request works in combination with mk. => => Starting here, isn't robust => text is typeset and thus not => in two columns. suited for a => Note that this real two-column => implementation macro. Several escape sequences enable fine control of movement about the page. -- Escape sequence: \v'expr' Vertically move the drawing position. EXPR indicates the magnitude of motion: positive is downward and and negative upward. The default scaling unit is 'v'. The motion is relative to the current drawing position unless EXPR begins with the boundary-relative motion operator '|'. *Note Numeric Expressions::. Text processing continues at the new drawing position; usually, vertical motions should be in balanced pairs to avoid a confusing page layout. '\v' will not spring a vertical position trap. This can be useful; for example, consider a page bottom trap macro that prints a marker in the margin to indicate continuation of a footnote. *Note Traps::. A few escape sequences that produce vertical motion are unusual. They are thought to originate early in AT&T 'nroff' history to achieve super- and subscripting by half-line motions on line printers and teletypewriters before the phototypesetter made more precise positioning available. They are reckoned in ems--not vees--to maintain continuity with their original purpose of moving relative to the size of the type rather than the distance between text baselines (vees).(1) (*note Page Motions-Footnote-1::) -- Escape sequence: \r -- Escape sequence: \u -- Escape sequence: \d Move upward 1m, upward .5m, and downward .5m, respectively. Let us see these escape sequences in use. Obtain 100 cm\u3\d of \ka\d\092\h'|\nau'\r233\dU. In the foregoing we have paired '\u' and '\d' to typeset a superscript, and later a full em negative ("reverse") motion to place a superscript above a subscript. A numeral-width horizontal motion escape sequence aligns the proton and nucleon numbers, while '\k' marks a horizontal position to which '\h' returns so that we could stack them. (We shall discuss these horizontal motion escape sequences presently.) In serious applications, we often want to alter the type size of the -scripts and to fine-tune the vertical motions, as the 'groff' 'ms' package does with its super- and subscripting string definitions. -- Escape sequence: \h'expr' Horizontally move the drawing position. EXPR indicates the magnitude of motion: positive is rightward and negative leftward. The default scaling unit is 'm'. The motion is relative to the current drawing position unless EXPR begins with the boundary-relative motion operator '|'. *Note Numeric Expressions::. The following string definition sets the TeX logo.(2) (*note Page Motions-Footnote-2::) .ds TeX T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X\" There are a number of special-case escape sequences for horizontal motion. -- Escape sequence: \ Move right one word space. (The input is a backslash followed by a space.) This escape sequence can be thought of as a non-adjustable, unbreakable space. Usually you want '\~' instead; see *note Manipulating Filling and Adjustment::. -- Escape sequence: \| Move one-sixth em to the right on typesetting output devices. If a glyph named '\|' is defined in the current font, its width is used instead, even on terminal output devices. -- Escape sequence: \^ Move one-twelfth em to the right on typesetting output devices. If a glyph named '\^' is defined in the current font, its width is used instead, even on terminal output devices. -- Escape sequence: \0 Move right by the width of a numeral in the current font. Horizontal motions are not discarded at the end of an output line as word spaces are. *Note Breaking::. -- Escape sequence: \w'anything' -- Register: \n[st] -- Register: \n[sb] -- Register: \n[rst] -- Register: \n[rsb] -- Register: \n[ct] -- Register: \n[ssc] -- Register: \n[skw] Interpolate the width of ANYTHING in basic units. This escape sequence allows several properties of formatted output to be measured without writing it out. The length of the string 'abc' is \w'abc'u. => The length of the string 'abc' is 72u. ANYTHING is processed in a dummy environment: this means that font and type size changes, for example, may occur within it without affecting subsequent output. After each use, '\w' sets several registers. 'st' 'sb' The maximum vertical displacements of the text baseline above and below, respectively. The sign convention is opposite that of relative vertical motions; that is, depth below the (original) baseline is negative. These registers are incorrectly documented in the AT&T 'troff' manual as "the highest and lowest extent of [the argument to '\w'] relative to the baseline". 'rst' 'rsb' Like 'st' and 'sb', but taking account of the heights and depths of glyphs. In other words, these registers store the highest and lowest vertical positions attained by ANYTHING, doing what AT&T 'troff' documented 'st' and 'sb' as doing. 'ct' Characterizes the geometry of glyphs occurring in ANYTHING. 0 only short glyphs, no descenders or tall glyphs 1 at least one descender 2 at least one tall glyph 3 at least one each of a descender and a tall glyph 'ssc' The amount of horizontal space (possibly negative) that should be added to the last glyph before a subscript. 'skw' How far to right of the center of the last glyph in the '\w' argument, the center of an accent from a roman font should be placed over that glyph. -- Escape sequence: \kp -- Escape sequence: \k(ps -- Escape sequence: \k[position] Store the current horizontal position in the _input_ line in a register with the name POSITION (one-character name P, two-character name PS). Use this, for example, to return to the beginning of a string for highlighting or other decoration. -- Register: \n[hp] The current horizontal position at the input line. -- Register: \n[.k] A read-only register containing the current horizontal output position (relative to the current indentation). -- Escape sequence: \o'abc...' Overstrike the glyphs of characters A, B, C, ...; the glyphs are centered, written, and the drawing position advanced by the widest of the glyphs. -- Escape sequence: \zc Format the character C with zero width; that is, without advancing the drawing position. Use '\z' to overstrike glyphs aligned to their left edges, in contrast to '\o''s centering. -- Escape sequence: \Z'anything' Save the drawing position, format ANYTHING, then restore it. Tabs and leaders in the argument are ignored with an error diagnostic. We might implement a strike-through macro thus. .de ST .nr width \w'\\$1' \Z@\v'-.25m'\l'\\n[width]u'@\\$1 .. . This is .ST "a test" an actual emergency!  File: groff.info, Node: Page Motions-Footnotes, Up: Page Motions (1) At the 'grops' defaults of 10-point type on 12-point vertical spacing, the difference between half a vee and half an em can be subtle: large spacings like '.vs .5i' make it obvious. (2) *Note Strings::, for an explanation of the trailing '\"'.  File: groff.info, Node: Drawing Geometric Objects, Next: Traps, Prev: Page Motions, Up: GNU troff Reference 5.26 Drawing Geometric Objects ============================== A few of the formatter's escape sequences draw lines and other geometric objects. Combined with each other and with page motion commands (*note Page Motions::), a wide variety of figures is possible. For complex drawings, these operations can be cumbersome; the preprocessors 'gpic' or 'ggrn' are typically used instead. The '\l' and '\L' escape sequences draw horizontal and vertical sequences of glyphs, respectively. Even the simplest of output devices supports them. -- Escape sequence: \l'l' -- Escape sequence: \l'lc' Draw a horizontal line of length L from the drawing position. Rightward motion is positive. Afterward, the drawing position is at the right end of the line. The default scaling unit is 'm'. The optional second parameter C is a character with which to draw the line. The default is the baseline rule special character, '\[ru]'. If C is a valid scaling unit, put '\&' after L to disambiguate the input. .de textbox \[br]\\$*\[br]\l'|0\[rn]'\l'|0\[ul]' .. The foregoing outputs a box rule (a vertical line), the text argument(s), and another box rule. We employ the boundary-relative motion operator '|'. Finally, the line-drawing escape sequences draw a radical extender (a form of overline) and an underline from the drawing position to the position coresponding to beginning of the _input_ line. The drawing position returns to just after the right-hand box rule because the lengths of the drawn lines are negative, as noted above. -- Escape sequence: \L'l' -- Escape sequence: \L'lc' Draw a vertical line of length L from the drawing position. Downward motion is positive. The default scaling unit is 'v'. The default character is the box rule, '\[br]'. As with vertical motion escape sequences, text processing continues where the line ends. '\L' is otherwise similar to '\l'. $ nroff < This is a => | => | => |test. When writing text, the drawing position is at the text baseline; recall *note Page Geometry::. The '\D' escape sequence provides "drawing commands" that direct the output device to render geometrical objects rather than glyphs. Specific devices may support only a subset, or may feature additional ones; consult the man page for the output driver in use. Terminal devices in particular implement almost none. *Note Graphics Commands::. Rendering starts at the drawing position; when finished, the drawing position is left at the rightmost point of the object, even for closed figures, except where noted. GNU 'troff' draws stroked (outlined) objects with the stroke color, and shades filled ones with the fill color. *Note Colors::. Coordinates H and V are horizontal and vertical motions relative to the drawing position or previous point in the command. The default scaling unit for horizontal measurements (and diameters of circles) is 'm'; for vertical ones, 'v'. Circles, ellipses, and polygons can be drawn filled or stroked. These are independent properties; if you want a filled, stroked figure, you must draw the same figure twice using each drawing command. A filled figure is always smaller than an outlined one because the former is drawn only within its defined area, whereas strokes have a line thickness (set with '\D't''). \h'1i'\v'1i'\ \# increase line thickness \Z'\D't 5p''\ \# draw stroked (unfilled) polygon \Z'\D'p 3 3 -6 0''\ \# draw filled (solid) polygon \Z'\D'P 3 3 -6 0'' -- Escape sequence: \D'command argument ...' Drawing command escape sequence parameters begin with an ordinary character, COMMAND, selecting the type of object to be drawn, followed by ARGUMENTs whose meaning is determined by COMMAND. '\D'~ H1 V1 ... HN VN'' Draw a B-spline to each point in sequence, leaving the drawing position at (HN, VN). '\D'a HC VC H V'' Draw a circular arc centered at (HC, VC) counterclockwise from the drawing position to a point (H, V) relative to the center. (1) (*note Drawing Geometric Objects-Footnote-1::) '\D'c D'' Draw a circle of diameter D with its leftmost point at the drawing position. '\D'C D'' As '\D'C ...'', but the circle is filled. '\D'e H V'' Draw an ellipse of width H and height V with its leftmost point at the drawing position. '\D'E X Y'' As '\D'e ...'', but the ellipse is filled. '\D'l DX DY'' Draw line from the drawing position to (H, V). The following is a macro for drawing a box around a text argument; for simplicity, the box margin is a fixed at 0.2m. .de TEXTBOX . nr @wd \w'\\$1' \h'.2m'\ \h'-.2m'\v'(.2m - \\n[rsb]u)'\ \D'l 0 -(\\n[rst]u - \\n[rsb]u + .4m)'\ \D'l (\\n[@wd]u + .4m) 0'\ \D'l 0 (\\n[rst]u - \\n[rsb]u + .4m)'\ \D'l -(\\n[@wd]u + .4m) 0'\ \h'.2m'\v'-(.2m - \\n[rsb]u)'\ \\$1\ \h'.2m' .. The argument is measured with the '\w' escape sequence. Its width is stored in register '@wd'. '\w' also sets the registers 'rst' and 'rsb'; these contain its maximum vertical extents of the argument. Then, four lines are drawn to form a box, offset by the box margin. '\D'p H1 V1 ... HN VN'' Draw polygon with vertices at drawing position and each point in sequence. GNU 'troff' closes the polygon by drawing a line from (HN, VN) back to the initial drawing position. Afterward, the drawing position is left at (HN, VN). '\D'P DX1 DY1 DX2 DY2 ...'' As '\D'P ...'', but the polygon is filled. The following macro is like the '\D'l'' example, but shades the box. We draw the box before writing the text because colors in GNU 'troff' have no transparency; in othe opposite order, the filled polygon would occlude the text. .de TEXTBOX . nr @wd \w'\\$1' \h'.2m'\ \h'-.2m'\v'(.2m - \\n[rsb]u)'\ \M[lightcyan]\ \D'P 0 -(\\n[rst]u - \\n[rsb]u + .4m) \ (\\n[@wd]u + .4m) 0 \ 0 (\\n[rst]u - \\n[rsb]u + .4m) \ -(\\n[@wd]u + .4m) 0'\ \h'.2m'\v'-(.2m - \\n[rsb]u)'\ \M[]\ \\$1\ \h'.2m' .. '\D't N'' Set the stroke thickness of geometric objects to N basic units. A zero N selects the minimal supported thickness. A negative N selects a thickness proportional to the type size; this is the default. In a hazy penumbra between text rendering and drawing commands we locate the bracket-building escape sequence, '\b'. It can assemble apparently large glyphs by vertically stacking ordinary ones. -- Escape sequence: \b'contents' Pile and center a sequence of glyphs vertically on the output line. "Piling" stacks glyphs corresponding to each character in CONTENTS, read from left to right, and placed from top to bottom. GNU 'troff' separates the glyphs vertically by 1m, and the pile itself is centered 0.5m above the text baseline. The horizontal drawing position is then advanced by the width of the widest glyph in the pile. This rather inflexible positioning algorithm doesn't work with the 'dvi' output device since its bracket pieces vary in height. Instead, use the 'geqn' preprocessor. *note Manipulating Spacing:: describes how to adjust the vertical spacing of the output line with the '\x' escape sequence. The application of '\b' that lends its name is construction of brackets, braces, and parentheses when typesetting mathematics. We might construct a large opening (left) brace as follows. \b'\[lt]\[bv]\[lk]\[bv]\[lb]' See 'groff_char(7)' for a list of special character identifiers.  File: groff.info, Node: Drawing Geometric Objects-Footnotes, Up: Drawing Geometric Objects (1) (HC, VC) is adjusted to the point nearest the perpendicular bisector of the arc's chord.  File: groff.info, Node: Deferring Output, Next: Traps, Prev: Drawing Geometric Objects, Up: GNU troff Reference 5.27 Deferring Output ===================== A few 'roff' language elements are generally not used in simple documents, but arise as page layouts become more sophisticated and demanding. "Environments" collect formatting parameters like line length and typeface. A "diversion" stores formatted output for later use. A "trap" is a condition on the input or output, tested automatically by the formatter, that is associated with a macro, causing it to be called when that condition is fulfilled. Footnote support often exercises all three of the foregoing features. A simple implementation might work as follows. A pair of macros is defined: one starts a footnote and the other ends it. The author calls the first macro where a footnote marker is desired. The macro establishes a diversion so that the footnote text is collected at the place in the body text where its corresponding marker appears. An environment is created for the footnote so that it is set at a smaller typeface. The footnote text is formatted in the diversion using that environment, but it does not yet appear in the output. The document author calls the footnote end macro, which returns to the previous environment and ends the diversion. Later, after much more body text in the document, a trap, set a small distance above the page bottom, is sprung. The macro called by the trap draws a line across the page and emits the stored diversion. Thus, the footnote is rendered. Diversions and traps make the text formatting process non-linear. Let us imagine a set of text lines or paragraphs labelled 'A', 'B', and so on. If we set up a trap that produces text 'T' (as a page footer, say), and we also use a diversion to store the formatted text 'D', then a document with input text in the order 'A B C D E F' might render as 'A B C E T F'. The diversion 'D' will never be output if we do not call for it. Environments of themselves are not a source of non-linearity in document formatting: environment switches have immediate effect. One could always write a macro to change as many formatting parameters as desired with a single convenient call. But because diversions can be nested and macros called by traps that are sprung by other trap-called macros, they may be called upon in varying contexts. For example, consider a page header that is always to be set in Helvetica. A document that uses Times for most of its body text, but Courier for displayed code examples, poses a challenge if a page break occurs in the middle of a code display; if the header trap assumes that the "previous font" is always Times, the rest of the example will be formatted in the wrong typeface. One could carefully save all formatting parameters upon entering the trap and restore them upon leaving it, but this is verbose, error-prone, and not future-proof as the 'groff' language develops. Environments save us considerable effort.  File: groff.info, Node: Traps, Next: Diversions, Prev: Deferring Output, Up: GNU troff Reference 5.28 Traps ========== "Traps" are locations in the output or conditions on the input that, when reached or fulfilled, call a specified macro. These traps can occur at a given location on the page, at a given location in the current diversion (together, these are known as vertical position traps), at a blank line, at a line with leading space characters, after a quantity of input lines, or at the end of input. Macros called by traps are passed no arguments. Setting a trap is also called "planting" one. It is said that a trap is "sprung" if its condition is fulfilled. * Menu: * Vertical Position Traps:: * Diversion Traps:: * Input Line Traps:: * Blank Line Traps:: * Leading Space Traps:: * End-of-input Traps::  File: groff.info, Node: Vertical Position Traps, Next: Page Location Traps, Prev: Traps, Up: Traps 5.28.1 Vertical Position Traps ------------------------------ A "vertical position trap" calls a macro when the formatter's vertical drawing position reaches or passes, in the downward direction, a certain location on the output page or in a diversion. Its applications include setting page headers and footers, body text in multiple columns, and footnotes. -- Request: .vpt [flag] -- Register: \n[.vpt] Enable vertical position traps if FLAG is non-zero or absent; disable them otherwise. Vertical position traps are those set by the 'wh' request or by 'dt' within a diversion. The parameter that controls whether vertical position traps are enabled is global. Initially, vertical position traps are enabled. The current value is stored in the '.vpt' read-only register. A page can't be ejected if 'vpt' is set to zero; see *note The Implicit Page Trap::. * Menu: * Page Location Traps:: * The Implicit Page Trap:: * Diversion Traps::  File: groff.info, Node: Page Location Traps, Next: The Implicit Page Trap, Prev: Vertical Position Traps, Up: Vertical Position Traps 5.28.1.1 Page Location Traps ............................ A "page location trap" is a vertical position trap that applies to the page; that is, to undiverted output. Many can be present; manage them with the 'wh' and 'ch' requests. -- Request: .wh dist [name] Plant macro NAME as page location trap at DIST. The default scaling unit is 'v'. Non-negative values for DIST set the trap relative to the top of the page; negative values set the trap relative to the bottom of the page. It is not possible to plant a trap less than one basic unit from the page bottom: a DIST of '-0' is interpreted as '0', the top of the page.(1) (*note Page Location Traps-Footnote-1::) An existing _visible_ trap (see below) at DIST is removed; this is 'wh''s sole function if NAME is missing. A trap is sprung only if it is "visible", meaning that its location is reachable on the page(2) (*note Page Location Traps-Footnote-2::) and it is not hidden by another trap at the same location already planted there. A macro package might set headers and footers as follows; this example configures vertical margins of one inch to the body text, and one half-inch to the titles. Observe the use of the no-break control character with 'sp' request to position our text baselines, and the page number character '%' used with the 'tl' request. .\" hdfo.roff .de hd \" page header ' sp .5i ' tl '\\*(Ti''\\*(Da' \" title and date strings ' sp .5i .. .de fo \" page footer ' sp .5i . tl ''%'' . bp .. .wh 0 hd \" trap at top of the page .wh -1i fo \" trap 1 inch from bottom To use these traps, copy the above (or load it from a file with the 'so' or 'mso' requests), then set up the strings it uses. .so hdfo.roff .ds Ti Final Report\" .ds Da 21 May 2023\" .ti On 5 August of last year, this committee tasked me with the investigation of the CFIT (controlled flight into terrain) incident of .\" ...and so on... A trap above the top or at or below the bottom of the page can be made visible by either moving it into the page area or increasing the page length so that the trap is on the page. Negative trap values always use the _current_ page length; they are not converted to an absolute vertical position. We can use the 'ptr' request to dump our page location traps to the standard error stream (*note Debugging::). Their positions are reported in basic units; an 'nroff' device example follows. .pl 5i .wh -1i xx .ptr error-> xx -240 .pl 100i .ptr error-> xx -240 It is possible to have more than one trap at the same location (although only one at a time can be visible); to achieve this, the traps must be defined at different locations, then moved to the same place with the 'ch' request. In the following example, the many empty lines caused by the 'bp' request are not shown in the output. .de a . nop a .. .de b . nop b .. .de c . nop c .. . .wh 1i a .wh 2i b .wh 3i c .bp => a b c .ch b 1i .ch c 1i .bp => a .ch a 0.5i .bp => a b -- Register: \n[.t] The read-only register '.t' holds the distance to the next vertical position trap. If there are no traps between the current position and the bottom of the page, it contains the distance to the page bottom. Within a diversion, in the absence of a diversion trap, this distance is the largest representable integer in basic units--effectively infinite. -- Request: .ch name [dist] Change the location of a trap by moving macro NAME to new location DIST, or by unplanting it altogether if DIST is absent. The default scaling unit is 'v'. Parameters to 'ch' are specified in the opposite order from 'wh'. If NAME is the earliest planted macro of multiple traps at the same location, (re)moving it from that location exposes the macro next least recently planted at the same place.(3) (*note Page Location Traps-Footnote-3::) Changing a trap's location is useful for building up footnotes in a diversion to allow more space at the bottom of the page for them. The same macro can be installed simultaneously at multiple locations; however, only the earliest-planted instance--that has not yet been deleted with 'wh'--will be moved by 'ch'. The following example (using an 'nroff' device) illustrates this behavior. Blank lines have been elided from the output. .de T Trap sprung at \\n(nlu. .br .. .wh 1i T .wh 2i T foo .sp 11i .bp .ch T 4i bar .sp 11i .bp .ch T 5i baz .sp 11i .bp .wh 5i .ch T 6i qux .sp 11i => foo => Trap sprung at 240u. => Trap sprung at 480u. => bar => Trap sprung at 480u. => Trap sprung at 960u. => baz => Trap sprung at 480u. => Trap sprung at 1200u. => qux => Trap sprung at 1440u. -- Register: \n[.ne] The read-only register '.ne' contains the amount of space that was needed in the last 'ne' request that caused a trap to be sprung; it is useful in conjunction with the '.trunc' register. *Note Page Control::. Since the '.ne' register is set only by traps, it doesn't make sense to interpolate it outside of macros called by traps. -- Register: \n[.trunc] A read-only register containing the amount of vertical space truncated from an 'sp' request by the most recently sprung vertical position trap, or, if the trap was sprung by an 'ne' request, minus the amount of vertical motion produced by the 'ne' request. In other words, at the point a trap is sprung, it represents the difference of what the vertical position would have been but for the trap, and what the vertical position actually is. Since the '.trunc' register is set only by traps, it doesn't make sense to interpolate it outside of macros called by traps. -- Register: \n[.pe] This Boolean-valued, read-only register interpolates 1 while a page is being ejected, and 0 otherwise. In the following example, we plant the same trap at the top and the bottom of the page. We also make the trap report its name and the vertical drawing position. .de T .tm \\$0: page \\n%, nl=\\n[nl] .pe=\\n[.pe] .. .ll 46n .wh 0 T .wh -1v T Those who can make you believe absurdities can make you commit atrocities. \[em] Voltaire error-> T: page 1, nl=0 .pe=0 error-> T: page 1, nl=2600 .pe=1 => Those who can make you believe absurdities can => make you commit atrocities. -- Voltaire When designing macros, keep in mind that diversions and traps do normally interact. For example, if a trap calls a header macro (while outputting a diversion) that tries to change the font on the current page, the effect is not visible before the diversion has completely been printed (except for input protected with '\!' or '\?') since the data in the diversion is already formatted. In most cases, this is not the expected behaviour.  File: groff.info, Node: Page Location Traps-Footnotes, Up: Page Location Traps (1) *Note The Implicit Page Trap::. (2) A trap planted at '20i' or '-30i' will not be sprung on a page of length '11i'. (3) It may help to think of each trap location as maintaining a queue; 'wh' operates on the head of the queue, and 'ch' operates on its tail. Only the trap at the head of the queue is visible.  File: groff.info, Node: The Implicit Page Trap, Next: Diversion Traps, Prev: Page Location Traps, Up: Vertical Position Traps 5.28.1.2 The Implicit Page Trap ............................... If, after starting GNU 'troff' without loading a macro package, you use the 'ptr' request to dump a list of the active traps to the standard error stream,(1) (*note The Implicit Page Trap-Footnote-1::) nothing is reported. Yet the '.t' register will report a steadily decreasing value with every output line your document produces, and once the value of '.t' gets to within '.V' of zero, you will notice that something trap-like happens--the page is ejected, a new one begins, and the value of '.t' becomes large once more. This "implicit page trap" always exists in the top-level diversion;(2) (*note The Implicit Page Trap-Footnote-2::) it works like a trap in some ways but not others. Its purpose is to eject the current page and start the next one. It has no name, so it cannot be moved or deleted with 'wh' or 'ch' requests. You cannot hide it by placing another trap at its location, and can move it only by redefining the page length with 'pl'. Its operation is suppressed when vertical page traps are disabled with GNU 'troff''s 'vpt' request.  File: groff.info, Node: The Implicit Page Trap-Footnotes, Up: The Implicit Page Trap (1) *Note Debugging::. (2) *Note Diversions::.  File: groff.info, Node: Diversion Traps, Next: Input Line Traps, Prev: The Implicit Page Trap, Up: Vertical Position Traps 5.28.1.3 Diversion Traps ........................ A diversion is not formatted in the context of a page, so it lacks page location traps; instead it can have a "diversion trap". There can exist at most one such vertical position trap per diversion. -- Request: .dt [dist name] Set a trap _within_ a diversion at location DIST, which is interpreted relative to diversion rather than page boundaries. If invoked with fewer than two arguments, any diversion trap in the current diversion is removed. The register '.t' works within diversions. It is an error to invoke 'dt' in the top-level diversion. *Note Diversions::.  File: groff.info, Node: Input Line Traps, Next: Blank Line Traps, Prev: Diversion Traps, Up: Traps 5.28.2 Input Line Traps ----------------------- -- Request: .it [n name] -- Request: .itc [n name] Set an input line trap, calling macro NAME after processing the next N productive input lines (recall *note Manipulating Filling and Adjustment::). Any existing input line trap in the environment is replaced. Without arguments, 'it' and 'itc' clear any input line trap that has not yet sprung. Consider a macro '.ST S N' which sets the next N input lines in the font style S. .de ST \" Use style $1 for next $2 text lines. . it \\$2 ES . ft \\$1 .. .de ES \" end ST . ft R .. .ST I 1 oblique face .ST I 1 oblique\c face => oblique face obliqueface (second "face" upright) Unlike the 'ce' and 'rj' requests, 'it' counts lines interrupted with the '\c' escape sequence separately (*note Line Continuation::); 'itc' does not. To see the difference, let's change the previous example to use 'itc' instead. ... . itc \\$2 ES ... => oblique face obliqueface (second "face" oblique) You can think of the 'ce' and 'rj' requests as implicitly creating an input line trap with 'itc' that schedules a break when the trap is sprung. .de BR . br . internal: disable centering-without-filling .. . .de ce . if \\n[.br] .br . itc \\$1 BR . internal: enable centering-without-filling .. Let us consider in more detail the sorts of input lines that are or are not "productive". .de Trap TRAP SPRUNG .. .de Mac .if r a \l'5n' .. .it 2 Trap . foo .Mac bar baz .it 1 Trap .sp \" moves, but does not write or draw qux .itc 1 Trap \h'5n'\c \" moves, but does not write or draw jat When 'Trap' gets called depends on whether the 'a' register is defined; the control line with the 'if' request may or may not produce written output. We also see that the spacing request 'sp', while certainly affecting the output, does not spring the input line trap. Similarly, the horizontal motion escape sequence '\h' also affected the output, but was not "written". Observe that we had to follow it with '\c' and use 'itc' to prevent the newline at the end of the text line from causing a word break, which, like an ordinary space character, counts as written output. $ groff -Tascii input-trap-example.groff => foo bar TRAP SPRUNG baz => => qux TRAP SPRUNG jat TRAP SPRUNG $ groff -Tascii -ra1 input-trap-example.groff => foo _____ TRAP SPRUNG bar baz => => qux TRAP SPRUNG jat TRAP SPRUNG Input line traps are associated with the environment (*note Environments::); switching to another environment suspends the current input line trap, and going back resumes it, restoring the count of qualifying lines enumerated in that environment.  File: groff.info, Node: Blank Line Traps, Next: Leading Space Traps, Prev: Input Line Traps, Up: Traps 5.28.3 Blank Line Traps ----------------------- -- Request: .blm [name] Set a blank line trap, calling the macro NAME when GNU 'troff' encounters a blank line in an input file, instead of the usual behavior (*note Breaking::). A line consisting only of spaces is also treated as blank and subject to this trap. If no argument is supplied, the default blank line behavior is (re-)established.  File: groff.info, Node: Leading Space Traps, Next: End-of-input Traps, Prev: Blank Line Traps, Up: Traps 5.28.4 Leading Space Traps -------------------------- -- Request: .lsm [name] -- Register: \n[lsn] -- Register: \n[lss] Set a leading space trap, calling the macro NAME when GNU 'troff' encounters leading spaces in an input line; the implicit line break that normally happens in this case is suppressed. If no argument is supplied, the default leading space behavior is (re-)established (*note Breaking::). The count of leading spaces on an input line is stored in register 'lsn', and the amount of corresponding horizontal motion in register 'lss', irrespective of whether a leading space trap is set. When it is, the leading spaces are removed from the input line, and no motion is produced before calling NAME.  File: groff.info, Node: End-of-input Traps, Prev: Leading Space Traps, Up: Traps 5.28.5 End-of-input Traps ------------------------- -- Request: .em [name] Set a trap at the end of input, calling macro NAME after the last line of the last input file has been processed. If no argument is given, any existing end-of-input trap is removed. For example, if the document had to have a section at the bottom of the last page for someone to approve it, the 'em' request could be used. .de approval \c . ne 3v . sp (\\n[.t]u - 3v) . in +4i . lc _ . br Approved:\t\a . sp Date:\t\t\a .. . .em approval The '\c' in the above example needs explanation. For historical reasons (compatibility with AT&T 'troff'), the end-of-input macro exits as soon as it causes a page break if no partially collected line remains.(1) (*note End-of-input Traps-Footnote-1::) Let us assume that there is no '\c' in the above 'approval' macro, that the page is full, and last output line has been broken with, say, a 'br' request. Because there is no more room, a 'ne' request at this point causes a page ejection, which in turn makes 'troff' exit immediately as just described. In most situations, this is not desired; people generally want to format the input after 'ne'. To force processing of the whole end-of-input macro independently of this behavior, it is thus advisable to (invisibly) ensure the existence of a partially collected line ('\c') whenever there is a chance that a page break can happen. In the above example, invoking the 'ne' request ensures that there is room for the subsequent formatted output on the same page, so we need insert '\c' only once. The next example shows how to append three lines, then start a new page unconditionally. Since '.ne 1' doesn't give the desired effect--there is always one line available or we are already at the beginning of the next page--we temporarily increase the page length by one line so that we can use '.ne 2'. .de EM .pl +1v \c .ne 2 line one .br \c .ne 2 line two .br \c .ne 2 line three .br .pl -1v \c 'bp .. .em EM This specific feature affects only the first potential page break caused by the end-of-input macro; further page breaks emitted by the macro are handled normally. Another possible use of the 'em' request is to make GNU 'troff' emit a single large page instead of multiple pages. For example, one may want to produce a long plain text file for reading in a terminal or emulator without page footers and headers interrupting the body of the document. One approach is to set the page length at the beginning of the document to a very large value to hold all the text,(2) (*note End-of-input Traps-Footnote-2::) and automatically adjust it to the exact height of the document after the text has been output. .de adjust-page-length . br . pl \\n[nl]u \" \n[nl]: current vertical position .. . .de single-page-mode . pl 99999 . em adjust-page-length .. . .\" Activate the above code if configured. .if \n[do-continuous-rendering] \ . single-page-mode Since only one end-of-input trap exists and another macro package may already use it, care must be taken not to break the mechanism. A simple solution would be to append the above macro to the macro package's end-of-input macro using the 'am' request.  File: groff.info, Node: End-of-input Traps-Footnotes, Up: End-of-input Traps (1) While processing an end-of-input macro, the formatter assumes that the next page break must be the last; it goes into "sudden death overtime". (2) Another, taken by the 'groff' 'man' macros, is to intercept 'ne' requests and wrap 'bp' ones.  File: groff.info, Node: Diversions, Next: Punning Names, Prev: Traps, Up: GNU troff Reference 5.29 Diversions =============== In 'roff' systems it is possible to format text as if for output, but instead of writing it immediately, one can "divert" the formatted text into a named storage area. It is retrieved later by specifying its name after a control character. The same name space is used for such diversions as for strings and macros; see *note Identifiers::. Such text is sometimes said to be "stored in a macro", but this coinage obscures the important distinction between macros and strings on one hand and diversions on the other; the former store _unformatted_ input text, and the latter capture _formatted_ output. Diversions also do not interpret arguments. Applications of diversions include "keeps" (preventing a page break from occurring at an inconvenient place by forcing a set of output lines to be set as a group), footnotes, tables of contents, and indices. For orthogonality it is said that GNU 'troff' is in the "top-level diversion" if no diversion is active (that is, formatted output is being "diverted" immediately to the output device). Dereferencing an undefined diversion will create an empty one of that name and cause a warning in category 'mac' to be emitted. *Note Warnings::, for information about the enablement and suppression of warnings. A diversion does not exist for the purpose of testing with the 'd' conditional operator until its initial definition ends (*note Operators in Conditionals::). The following requests are used to create and alter diversions. -- Request: .di [name] -- Request: .da [name] Start collecting formatted output in a diversion called NAME. The 'da' request appends to a diversion called NAME, creating it if necessary. If NAME already exists as an alias, the target of the alias is replaced or appended to; recall *note Strings::. The pending output line is diverted as well. Switching to another environment (with the 'ev' request) before invoking 'di' or 'da' avoids including any pending output line in the diversion; see *note Environments::. Invoking 'di' or 'da' without an argument stops diverting output to the diversion named by the most recent corresponding request. If 'di' or 'da' is called without an argument when there is no current diversion, a warning in category 'di' is produced. *Note Warnings::, for information about the enablement and suppression of warnings. Before the diversion. .di yyy In the diversion. .br .di After the diversion. .br => After the diversion. .yyy => Before the diversion. In the diversion. GNU 'troff' supports "box" requests to exclude a partially collected line from a diversion, as this is often desirable. -- Request: .box [name] -- Request: .boxa [name] Divert (or append) output to NAME, similarly to the 'di' and 'da' requests, respectively. Any pending output line is _not_ included in the diversion. Without an argument, stop diverting output; any pending output line inside the diversion is discarded. Before the box. .box xxx In the box. .br Hidden treasure. .box After the box. .br => Before the box. After the box. .xxx => In the box. Apart from pending output line inclusion and the request names that populate them, boxes are handled exactly as diversions are. All of the following 'groff' language elements can be used with them interchangeably. -- Register: \n[.z] -- Register: \n[.d] Diversions may be nested. The read-only string-valued register '.z' contains the name of the current diversion. The read-only register '.d' contains the current vertical place in the diversion. If the input text is not being diverted, '.d' reports the same location as the register 'nl'. -- Register: \n[.h] The read-only register '.h' stores the "high-water mark" on the current page or in the current diversion. It corresponds to the text baseline of the lowest line on the page.(1) (*note Diversions-Footnote-1::) .tm .h==\n[.h], nl==\n[nl] => .h==0, nl==-1 This is a test. .br .sp 2 .tm .h==\n[.h], nl==\n[nl] => .h==40, nl==120 As implied by the example, vertical motion does not produce text baselines and thus does not increase the value interpolated by '\n[.h]'. -- Register: \n[dn] -- Register: \n[dl] After completing a diversion, the writable registers 'dn' and 'dl' contain its vertical and horizontal sizes. Only the lines just processed are counted: for the computation of 'dn' and 'dl', the requests 'da' and 'boxa' are handled as if 'di' and 'box' had been used, respectively--lines that have been already stored in the diversion (box) are not taken into account. .\" Center text both horizontally and vertically. .\" Macro .(c starts centering mode; .)c terminates it. . .\" Disable the escape character with .eo so that we .\" don't have to double backslashes on the "\n"s. .eo .de (c . br . ev (c . evc 0 . in 0 . nf . di @c .. .de )c . br . ev . di . nr @s (((\n[.t]u - \n[dn]u) / 2u) - 1v) . sp \n[@s]u . ce 1000 . @c . ce 0 . sp \n[@s]u . br . fi . rr @s . rm @c .. .ec -- Escape sequence: \!anything -- Escape sequence: \?anything\? "Transparently" embed ANYTHING into the current diversion, preventing requests, macro calls, and escape sequences from being interpreted when read into a diversion. This is useful for preventing them from taking effect until the diverted text is actually output. The '\!' escape sequence transparently embeds input up to and including the end of the line. The '\?' escape sequence transparently embeds input until its own next occurrence. ANYTHING may not contain newlines; use '\!' by itself to embed newlines in a diversion. The escape sequence '\?' is also recognized in copy mode and turned into a single internal code; it is this code that terminates ANYTHING. Thus the following example prints 4. .nr x 1 .nf .di d \?\\?\\\\?\\\\\\\\nx\\\\?\\?\? .di .nr x 2 .di e .d .di .nr x 3 .di f .e .di .nr x 4 .f Both escape sequences read the data in copy mode. If '\!' is used in the top-level diversion, its argument is directly embedded into GNU 'troff''s intermediate output. This can be used, for example, to control a postprocessor that processes the data before it is sent to an output driver. The '\?' escape used in the top-level diversion produces no output at all; its argument is simply ignored. -- Request: .output contents Emit CONTENTS directly to GNU 'troff''s intermediate output (subject to copy mode interpretation); this is similar to '\!' used at the top level. An initial neutral double quote in CONTENTS is stripped to allow embedding of leading spaces. This request can't be used before the first page has started--if you get an error, simply insert '.br' before the 'output' request. Use with caution! It is normally only needed for mark-up used by a postprocessor that does something with the output before sending it to the output device, filtering out CONTENTS again. -- Request: .asciify div "Unformat" the diversion DIV in a way such that Unicode basic Latin (ASCII) characters, characters translated with the 'trin' request, space characters, and some escape sequences, that were formatted and diverted into DIV are treated like ordinary input characters when DIV is reread. Doing so can be useful in conjunction with the 'writem' request. 'asciify' can be also used for gross hacks; for example, the following sets register 'n' to 1. .tr @. .di x @nr n 1 .br .di .tr @@ .asciify x .x 'asciify' cannot return all items in a diversion to their source equivalent: nodes such as those produced by the '\N' escape sequence will remain nodes, so the result cannot be guaranteed to be a pure string. *Note Copy Mode::. Glyph parameters such as the type face and size are not preserved; use 'unformat' to achieve that. -- Request: .unformat div Like 'asciify', unformat the diversion DIV. However, 'unformat' handles only tabs and spaces between words, the latter usually arising from spaces or newlines in the input. Tabs are treated as input tokens, and spaces become adjustable again. The vertical sizes of lines are not preserved, but glyph information (font, type size, space width, and so on) is retained.  File: groff.info, Node: Diversions-Footnotes, Up: Diversions (1) Thus, the "water" gets "higher" proceeding _down_ the page.  File: groff.info, Node: Punning Names, Next: Environments, Prev: Diversions, Up: GNU troff Reference 5.30 Punning Names ================== Macros, strings, and diversions share a name space; recall *note Identifiers::. Internally, the same mechanism is used to store them. You can thus call a macro with string interpolation syntax and vice versa. .de subject Typesetting .. .de predicate rewards attention to detail .. \*[subject] \*[predicate]. Truly. => Typesetting => rewards attention to detail Truly. What went wrong? Strings don't contain newlines, but macros do. String interpolation placed a newline at the end of '\*[subject]', and the next thing on the input was a space. Then when '\*[predicate]' was interpolated, it was followed by the empty request '.' on a line by itself. If we want to use macros as strings, we must take interpolation behavior into account. .de subject Typesetting\\ .. .de predicate rewards attention to detail\\ .. \*[subject] \*[predicate]. Truly. => Typesetting rewards attention to detail. Truly. By ending each text line of the macros with an escaped '\', we get the desired effect (*note Line Continuation::).(1) (*note Punning Names-Footnote-1::) What would have happened if we had used only one backslash at a time instead? Interpolating a string does not hide existing macro arguments. We can also place the escaped newline outside the string interpolation instead of within the string definition. Thus, in a macro, a more efficient way of doing .xx \\$@ is \\*[xx]\\ The latter calling syntax doesn't change the value of '\$0', which is then inherited from the calling macro (*note Parameters::). Diversions can be also called with string syntax. It is sometimes convenient to copy one-line diversions to a string. .di xx the .ft I interpolation system .ft .br .di .ds yy This is a test of \*(xx\c \*(yy. => This is a test of the interpolation system. As the previous example shows, it is possible to store formatted output in strings. The '\c' escape sequence prevents the subsequent newline from being interpreted as a break (again, *note Line Continuation::). Copying multi-output line diversions produces unexpected results. .di xxx a funny .br test .br .di .ds yyy This is \*[xxx]\c \*[yyy]. => test This is a funny. Usually, it is not predictable whether a diversion contains one or more output lines, so this mechanism should be avoided. With AT&T 'troff', this was the only solution to strip off a final newline from a diversion. Another disadvantage is that the spaces in the copied string are already formatted, preventing their adjustment. This can cause ugly results. A clean solution to this problem is available in GNU 'troff', using the requests 'chop' to remove the final newline of a diversion, and 'unformat' to make the horizontal spaces adjustable again. .box xxx a funny .br test .br .box .chop xxx .unformat xxx This is \*[xxx]. => This is a funny test. *Note Gtroff Internals::.  File: groff.info, Node: Punning Names-Footnotes, Up: Punning Names (1) The backslash is doubled. *Note Copy Mode::.  File: groff.info, Node: Environments, Next: Suppressing Output, Prev: Diversions, Up: GNU troff Reference 5.31 Environments ================= As discussed in *note Deferring Output::, environments store most of the parameters that determine the appearance of text. A default environment named '0' exists when GNU 'troff' starts up; it is modified by formatting-related requests and escape sequences. You can create new environments and switch among them. Only one is current at any given time. Active environments are managed using a "stack", a data structure supporting "push" and "pop" operations. The current environment is at the top of the stack. The same environment name can be pushed onto the stack multiple times, possibly interleaved with others. Popping the environment stack does not destroy the current environment; it remains accessible by name and can be made current again by pushing it at any time. Environments cannot be renamed or deleted, and can only be modified when current. To inspect the environment stack, use the 'pev' request; see *note Debugging::. Environments store the following information. * a partially collected line, if any * data about the most recently output glyph and line (registers '.cdp', '.cht', '.csk', '.n', '.w') * typeface parameters (size, family, style, height and slant, inter-word and inter-sentence space sizes) * page parameters (line length, title length, vertical spacing, line spacing, indentation, line numbering, centering, right-alignment, underlining, hyphenation parameters) * filling enablement; adjustment enablement and mode * tab stops; tab, leader, escape, control, no-break control, hyphenation, and margin characters * input line traps * stroke and fill colors -- Request: .ev [ident] -- Register: \n[.ev] Enter the environment IDENT, which is created if it does not already exist, using the same parameters as for the default environment used at startup. With no argument, GNU 'troff' switches to the previous environment. Invoking 'ev' with an argument puts environment IDENT onto the top of the environment stack. (If it isn't already present in the stack, this is a proper push.) Without an argument, 'ev' pops the environment stack, making the previous environment current. It is an error to pop the environment stack with no previous environment available. The read-only string-valued register '.ev' contains the name of the current environment--the one at the top of the stack. .ev footnote-env .fam N .ps 6 .vs 8 .ll -.5i .ev ... .ev footnote-env \[dg] Observe the smaller text and vertical spacing. .ev We can familiarize ourselves with stack behavior by wrapping the 'ev' request with a macro that reports the contents of the '.ev' register to the standard error stream. .de EV . ev \\$1 . tm environment is now \\n[.ev] .. . .EV foo .EV bar .EV .EV baz .EV .EV .EV error-> environment is now foo error-> environment is now bar error-> environment is now foo error-> environment is now baz error-> environment is now foo error-> environment is now 0 error-> error: environment stack underflow error-> environment is now 0 -- Request: .evc environment Copy the contents of ENVIRONMENT to the current environment. The following environment data are not copied. * a partially collected line, if present; * the interruption status of the previous input line (due to use of the '\c' escape sequence); * the count of remaining lines to center, to right-justify, or to underline (with or without underlined spaces)--these are set to zero; * the activation status of temporary indentation; * input line traps and their associated data; * the activation status of line numbering (which can be reactivated with '.nm +0'); and * the count of consecutive hyphenated lines (set to zero). -- Register: \n[.w] -- Register: \n[.cht] -- Register: \n[.cdp] -- Register: \n[.csk] The '\n[.w]' register contains the width of the last glyph formatted in the environment. The '\n[.cht]' register contains the height of the last glyph formatted in the environment. The '\n[.cdp]' register contains the depth of the last glyph formatted in the environment. It is positive for glyphs extending below the baseline. The '\n[.csk]' register contains the "skew" (how far to the right of the glyph's center that GNU 'troff' should place an accent) of the last glyph formatted in the environment. -- Register: \n[.n] The '\n[.n]' register contains the length of the previous output line emitted in the environment.  File: groff.info, Node: Suppressing Output, Next: Colors, Prev: Environments, Up: GNU troff Reference 5.32 Suppressing Output ======================= -- Escape sequence: \O[num] Suppress GNU 'troff' output of glyphs and geometric objects. The sequences '\O2', '\O3', '\O4', and '\O5' are intended for internal use by 'grohtml'. '\O0' Disable the emission of glyphs and geometric objects to the output driver, provided that this sequence occurs at the outermost suppression level (see '\O3' and '\04' below). Horizontal motions corresponding to non-overstruck glyph widths still occur. '\O1' Enable the emission of glyphs and geometric objects to the output driver, provided that this sequence occurs at the outermost suppression level. '\O0' and '\O1' also reset the four registers 'opminx', 'opminy', 'opmaxx', and 'opmaxy' to -1. These four registers mark the top left and bottom right hand corners of a box encompassing all written or drawn output. '\O2' At the outermost suppression level, enable emission of glyphs and geometric objects, and write to the standard error stream the page number and values of the four aforementioned registers encompassing glyphs written since the last interpolation of a '\O' sequence, as well as the page offset, line length, image file name (if any), horizontal and vertical device motion quanta, and input file name. Numeric values are in basic units. '\O3' Begin a nested suppression level. 'grohtml' uses this mechanism to create images of output preprocessed with 'gpic', 'geqn', and 'gtbl'. At startup, GNU 'troff' is at the outermost suppression level. 'pre-grohtml' generates these sequences when processing the document, using GNU 'troff' with the 'ps' output device, Ghostscript, and the PNM tools to produce images in PNG format. They start a new page if the device is not 'html' or 'xhtml', to reduce the number of images crossing a page boundary. '\O4' End a nested suppression level. '\O[5PFILE]' At the outermost suppression level, write the name 'file' to the standard error stream at position P, which must be one of 'l', 'r', 'c', or 'i', corresponding to left, right, centered, and inline alignments within the document, respectively. FILE is a name associated with the production of the next image. -- Register: \n[.O] Output suppression nesting level applied by '\O3' and '\O4' escape sequences.  File: groff.info, Node: I/O, Next: Postprocessor Access, Prev: Suppressing Output, Up: GNU troff Reference 5.33 I/O ======== 'gtroff' has several requests for including files: -- Request: .so file -- Request: .soquiet file Replace the 'so' request's control line with the contents of the file named by the argument, "sourcing" it. FILE is sought in the directories specified by '-I' command-line option. If FILE does not exist, a warning in category 'file' is produced and the request has no further effect. *Note Warnings::, for information about the enablement and suppression of warnings. 'so' can be useful for large documents; e.g., allowing each chapter of a book to be kept in a separate file. However, files interpolated with 'so' are not preprocessed; to overcome this limitation, see the 'gsoelim(1)' man page. Since GNU 'troff' replaces the entire control line with the contents of a file, it matters whether 'file' is terminated with a newline or not. Assume that file 'xxx' contains only the word 'foo' without a trailing newline. $ printf 'foo' > xxx The situation is .so xxx bar. => The situation is foobar. 'soquiet' works the same way, except that no warning diagnostic is issued if FILE does not exist. -- Request: .pso command Read the standard output from the specified COMMAND and include it in place of the 'pso' request. It is an error to use this request in safer mode, which is the default. Invoke GNU 'troff' or a front end with the '-U' option to enable unsafe mode. The comment regarding a final newline for the 'so' request is valid for 'pso' also. -- Request: .mso file -- Request: .msoquiet file Identical to the 'so' and 'soquiet' requests, respectively, except that 'gtroff' searches for the specified FILE in the same directories as macro files for the '-m' command-line option. If the file name to be included has the form 'NAME.tmac' and it isn't found, these requests try to include 'tmac.NAME' and vice versa. -- Request: .trf file -- Request: .cf file Transparently output the contents of FILE. Each line is output as if it were preceded by '\!'; however, the lines are _not_ subject to copy mode interpretation. If the file does not end with a newline, 'trf' adds one. Both requests cause a break. When used in a diversion, these requests embed a node (*note Gtroff Internals::) in it that, when reread, causes the contents of FILE to be transparently copied to the output. In AT&T 'troff', the contents of FILE are immediately copied to the output regardless of whether there is a current diversion; this behaviour is so anomalous that it must be considered a bug. While 'cf' copies the contents of FILE completely unprocessed, 'trf' disallows characters such as NUL that are not valid 'gtroff' input characters (*note Identifiers::). For 'cf', within a diversion, "completely unprocessed" means that each line of a file to be inserted is handled as if it were preceded by '\!\\!'. To define a macro 'x' containing the contents of file 'f', use .ev 1 .di x .trf f .di .ev The calls to 'ev' prevent the partially collected output line from becoming part of the diversion (*note Diversions::). -- Request: .nx [file] Force 'gtroff' to continue processing of the file specified as an argument. If no argument is given, immediately jump to the end of file. -- Request: .rd [prompt [arg1 arg2 ...]] Read from standard input, and include what is read as though it were part of the input file. Text is read until a blank line is encountered. If standard input is a TTY input device (keyboard), write PROMPT to standard error, followed by a colon (or send BEL for a beep if no argument is given). Arguments after PROMPT are available for the input. For example, the line .rd data foo bar with the input 'This is \$2.' prints This is bar. Using the 'nx' and 'rd' requests, it is easy to set up form letters. The form letter template is constructed like this, putting the following lines into a file called 'repeat.let': .ce \*(td .sp 2 .nf .rd .sp .rd .fi Body of letter. .bp .nx repeat.let When this is run, a file containing the following lines should be redirected in. Requests included in this file are executed as though they were part of the form letter. The last block of input is the 'ex' request, which tells GNU 'troff' to stop processing. If this were not there, 'troff' would not know when to stop. Trent A. Fisher 708 NW 19th Av., #202 Portland, OR 97209 Dear Trent, Len Adollar 4315 Sierra Vista San Diego, CA 92103 Dear Mr. Adollar, .ex -- Request: .pi pipe Pipe the output of 'gtroff' to the shell command(s) specified by PIPE. This request must occur before 'gtroff' has a chance to print anything. It is an error to use this request in safer mode, which is the default. Invoke GNU 'troff' or a front end with the '-U' option to enable unsafe mode. Multiple calls to 'pi' are allowed, acting as a chain. For example, .pi foo .pi bar ... is the same as '.pi foo | bar'. The intermediate output format of GNU 'troff' is piped to the specified commands. Consequently, calling 'groff' without the '-Z' option normally causes a fatal error. -- Request: .sy cmds -- Register: \n[systat] Execute the shell command(s) specified by CMDS. The output is not saved anywhere, so it is up to the user to do so. It is an error to use this request in safer mode; this is the default. Give GNU 'troff' or a front end program the '-U' option to enable unsafe mode. The following code fragment introduces the current time into a document. .sy perl -e 'printf ".nr H %d\\n.nr M %d\\n.nr S %d\\n",\ (localtime(time))[2,1,0]' > /tmp/x\n[$$] .so /tmp/x\n[$$] .sy rm /tmp/x\n[$$] \nH:\nM:\nS This works by having the Perl script (run by 'sy') write 'nr' requests that set the registers 'H', 'M', and 'S' to a temporary file. The 'roff' document then reads the temporary file using the 'so' request. The registers 'seconds', 'minutes', and 'hours', initialized at startup of GNU 'troff', should satisfy most requirements. Use the 'af' request to format their values for output. .af hours 00 .af minutes 00 .af seconds 00 \n[hours]:\n[minutes]:\n[seconds] => 02:17:54 The writable register 'systat' contains the return value of the 'system()' function executed by the last 'sy' request. -- Request: .open stream file -- Request: .opena stream file Open the specified FILE for writing and associates the specified STREAM with it. The 'opena' request is like 'open', but if the file exists, append to it instead of truncating it. It is an error to use these requests in safer mode; this is the default. Give GNU 'troff' or a front end program the '-U' option to enable unsafe mode. -- Request: .write stream data -- Request: .writec stream data Write to the file associated with the specified STREAM. The stream must previously have been the subject of an open request. The remainder of the line is interpreted as the 'ds' request reads its second argument: an initial neutral double quote in CONTENTS is stripped to allow embedding of leading spaces, and it is read in copy mode. The 'writec' request is like 'write', but only 'write' appends a newline to the data. -- Request: .writem stream xx Write the contents of the macro or string XX to the file associated with the specified STREAM. XX is read in copy mode, i.e., already formatted elements are ignored. Consequently, diversions must be unformatted with the 'asciify' request before calling 'writem'. Usually, this means a loss of information. -- Request: .close stream Close the specified STREAM; the stream is no longer an acceptable argument to the 'write' request. Here a simple macro to write an index entry. .open idx test.idx . .de IX . write idx \\n[%] \\$* .. . .IX test entry . .close idx -- Escape sequence: \Ve -- Escape sequence: \V(ev -- Escape sequence: \V[env] Interpolate the contents of the specified environment variable ENV (one-character name E, two-character name EV) as returned by the function 'getenv(3)'. '\V' is interpreted even in copy mode (*note Copy Mode::).  File: groff.info, Node: Postprocessor Access, Next: Miscellaneous, Prev: I/O, Up: GNU troff Reference 5.34 Postprocessor Access ========================= Two escape sequences and two requests enable documents to pass information directly to a postprocessor. These are useful for exercising device-specific capabilities that the 'groff' language does not abstract or generalize; examples include the embedding of hyperlinks and image files. Device-specific functions are documented in each output driver's man page, such as 'gropdf(1)', 'grops(1)', or 'grotty(1)'. -- Request: .device xxx ... -- Escape sequence: \X'xxx ...' Embed all XXX arguments into GNU 'troff' output as parameters to a device control command 'x X'. The meaning and interpretation of such parameters is determined by the output driver or other postprocessor. The 'device' request processes its arguments in copy mode (*note Copy Mode::). An initial neutral double quote in CONTENTS is stripped to allow embedding of leading spaces. By contrast, within '\X' arguments, the escape sequences '\&', '\)', '\%', and '\:' are ignored; '\' and '\~' are converted to single space characters; and '\\' has its escape character stripped. So that the basic Latin subset of the Unicode character set(1) (*note Postprocessor Access-Footnote-1::) can be reliably encoded in device control commands, seven special character escape sequences ('\-', '\[aq]', '\[dq]', '\[ga]', '\[ha]', '\[rs]', and '\[ti]',) are mapped to basic Latin characters; see the 'groff_char(7)' man page. For this transformation, character translations and special character definitions are ignored.(2) (*note Postprocessor Access-Footnote-2::) The use of any other escape sequence in '\X' parameters is normally an error. If the 'use_charnames_in_special' directive appears in the output device's 'DESC' file, the use of special character escape sequences is _not_ an error; they are simply output verbatim (with the exception of the seven mapped to Unicode basic Latin characters, discussed above). 'use_charnames_in_special' is currently employed only by 'grohtml'. -- Request: .devicem name -- Escape sequence: \Yn -- Escape sequence: \Y(nm -- Escape sequence: \Y[name] This is approximately equivalent to '\X'\*[NAME]'' (one-character name N, two-character name NM). However, the contents of the string or macro NAME are not interpreted; also it is permitted for NAME to have been defined as a macro and thus contain newlines (it is not permitted for the argument to '\X' to contain newlines). The inclusion of newlines requires an extension to the AT&T 'troff' output format, and confuses drivers that do not know about this extension (*note Device Control Commands::). -- Request: .tag name -- Request: .taga name Reserved for internal use.  File: groff.info, Node: Postprocessor Access-Footnotes, Up: Postprocessor Access (1) that is, ISO 646:1991-IRV or, popularly, "US-ASCII" (2) They are bypassed because these parameters are not rendered as glyphs in the output; instead, they remain abstract characters--in a PDF bookmark or a URL, for example.  File: groff.info, Node: Miscellaneous, Next: Gtroff Internals, Prev: Postprocessor Access, Up: GNU troff Reference 5.35 Miscellaneous ================== We document here GNU 'troff' features that fit poorly elsewhere. -- Request: .nm [start [increment [space [indentation]]]] -- Register: \n[ln] -- Register: \n[.nm] Begin (or, with no arguments, cease) numbering output lines. START assigns the number of the _next_ output line. Only line numbers divisible by INCREMENT are marked (default: '1'). SPACE configures the horizontal spacing between the number and the text (default: '1'). Any given INDENTATION is applied to the numbers (default: '0'). The third and fourth arguments are reckoned in numeral widths ('\0'). START must be non-negative and INCREMENT positive. The formatter aligns the number to the right in a width of three numeral spaces plus INDENTATION, then catenates SPACE and the output line. The line length is _not_ reduced. Depending on the value of the page offset,(1) (*note Miscellaneous-Footnote-1::) numbers wider than the allocated space protrude into the left margin, or shift the output line to the right. Line numbering parameters corresponding to missing arguments are not altered. After numbering is disabled, '.nm +0' resumes it using the previously active parameters. The parameters of 'nm' are associated with the environment (*note Environments::). While numbering is enabled, the output line number register 'ln' is updated as each line is output, even if no line number is formatted with it because it is being skipped (it is not a multiple of INCREMENT) or because numbering is suppressed (see the 'nn' request below). The '.nm' register tracks the enablement status of numbering. Temporary suspension of numbering with the 'nn' request does _not_ alter its value. .po 5n .ll 44n Programming, when stripped of all its circumstantial irrelevancies, .nm 999 1 1 -4 boils down to no more and no less than .nm +0 3 very effective thinking so as to avoid unmastered .nn 2 complexity, to very vigorous separation of your many different concerns. .br \(em Edsger Dijkstra .sp .nm 1 1 1 This guy's arrogance takes your breath away. .br \(em John Backus => Programming, when stripped of all its cir- => 999 cumstantial irrelevancies, boils down to no => more and no less than very effective think- => ing so as to avoid unmastered complexity, to => very vigorous separation of your many dif- => ferent concerns. => 1002 -- Edsger Dijkstra => => 1 This guy's arrogance takes your breath away. => 2 -- John Backus -- Request: .nn [skip] -- Register: \n[.nn] Suppress numbering of the next SKIP output lines that would otherwise be numbered. The default is 1. 'nn' can be invoked when line numbering is not active; suppression of numbering will take effect for SKIP lines once 'nm' enables it. The '.nn' register stores the count of output lines still to have their numbering suppressed. This count is associated with the environment (*note Environments::). To test whether the current output line will be numbered, you must check both the '.nm' and '.nn' registers. .de is-numbered . nop This line . ie (\\n[.nm] & (1-\\n[.nn])) IS . el ISN'T . nop numbered. . br .. Test line numbering. .is-numbered .nm 1 .nn 1 .is-numbered .is-numbered .nm .is-numbered => Test line numbering. This line ISN'T numbered. => This line ISN'T numbered. => 1 This line IS numbered. => This line ISN'T numbered. -- Request: .mc [margin-character [distance] Begin (or, with no arguments, cease) writing a "margin-character" to the right of each output line. The DISTANCE argument separates MARGIN-CHARACTER from the right margin. If absent, the most recent value is used; the default is 10 points. If an output line exceeds the line length, the margin character is appended to it. No margin character is written on lines produced by the 'tl' request. The margin character is a property of the output line; the margin character last configured when the line is output controls. If the margin character is disabled before an output line breaks, none is output (but see below). The margin character is associated with the environment (*note Environments::). .ll 5i .nf .mc \[br] This paragraph is marked with a margin character. .sp As seen above, vertical space isn't thus marked. \& An output line that is present, but empty, is. => This paragraph is marked with a margin character. | => => As seen above, vertical space isn't thus marked. | => | => An output line that is present, but empty, is. | For compatibility with AT&T 'troff', a call to 'mc' to set the margin character can't be undone immediately; at least one line gets a margin character. .ll 10n .nf .mc | .mc * .mc foo bar => foo * => bar The margin character mechanism is commonly used to annotate changes in documents. The 'groff' distribution ships a program, 'gdiffmk', to assist with this task.(2) (*note Miscellaneous-Footnote-2::) -- Request: .psbb file -- Register: \n[llx] -- Register: \n[lly] -- Register: \n[urx] -- Register: \n[ury] Retrieve the bounding box of the PostScript image found in FILE, which must conform to Adobe's "Document Structuring Conventions" (DSC), locate a '%%BoundingBox' comment, and store the (upper-, lower-, -left, -right) values into the registers 'llx', 'lly', 'urx', and 'ury'. If an error occurs (for example, if no '%%BoundingBox' comment is present), the formatter sets these registers to 0. The search path for FILE can be controlled with the '-I' command-line option.  File: groff.info, Node: Miscellaneous-Footnotes, Up: Miscellaneous (1) Recall *note Line Layout::. (2) Historically, tools named 'nrchbar' and 'changebar' were developed for marking changes with margin characters and could be found in archives of the 'comp.sources.unix' USENET group. Some proprietary Unices also offer(ed) a 'diffmk' program.  File: groff.info, Node: Gtroff Internals, Next: Debugging, Prev: Miscellaneous, Up: GNU troff Reference 5.36 'gtroff' Internals ======================= 'gtroff' processes input in three steps. One or more input characters are converted to an "input token".(1) (*note Gtroff Internals-Footnote-1::) Then, one or more input tokens are converted to an "output node". Finally, output nodes are converted to the intermediate output language understood by all output devices. Actually, before step one happens, 'gtroff' converts certain escape sequences into reserved input characters (not accessible by the user); such reserved characters are used for other internal processing also - this is the very reason why not all characters are valid input. *Note Identifiers::, for more on this topic. For example, the input string 'fi\[:u]' is converted into a character token 'f', a character token 'i', and a special token ':u' (representing u umlaut). Later on, the character tokens 'f' and 'i' are merged to a single output node representing the ligature glyph 'fi' (provided the current font has a glyph for this ligature); the same happens with ':u'. All output glyph nodes are 'processed', which means that they are invariably associated with a given font, font size, advance width, etc. During the formatting process, 'gtroff' itself adds various nodes to control the data flow. Macros, diversions, and strings collect elements in two chained lists: a list of input tokens that have been passed unprocessed, and a list of output nodes. Consider the following diversion. .di xxx a \!b c .br .di It contains these elements. node list token list element number line start node -- 1 glyph node 'a' -- 2 word space node -- 3 -- 'b' 4 -- '\n' 5 glyph node 'c' -- 6 vertical size node -- 7 vertical size node -- 8 -- '\n' 9 Elements 1, 7, and 8 are inserted by 'gtroff'; the latter two (which are always present) specify the vertical extent of the last line, possibly modified by '\x'. The 'br' request finishes the pending output line, inserting a newline input token, which is subsequently converted to a space when the diversion is reread. Note that the word space node has a fixed width that isn't adjustable anymore. To convert horizontal space nodes back to input tokens, use the 'unformat' request. Macros only contain elements in the token list (and the node list is empty); diversions and strings can contain elements in both lists. The 'chop' request simply reduces the number of elements in a macro, string, or diversion by one. Exceptions are "compatibility save" and "compatibility ignore" input tokens, which are ignored. The 'substring' request also ignores those input tokens. Some requests like 'tr' or 'cflags' work on glyph identifiers only; this means that the associated glyph can be changed without destroying this association. This can be very helpful for substituting glyphs. In the following example, we assume that glyph 'foo' isn't available by default, so we provide a substitution using the 'fchar' request and map it to input character 'x'. .fchar \[foo] foo .tr x \[foo] Now let us assume that we install an additional special font 'bar' that has glyph 'foo'. .special bar .rchar \[foo] Since glyphs defined with 'fchar' are searched before glyphs in special fonts, we must call 'rchar' to remove the definition of the fallback glyph. Anyway, the translation is still active; 'x' now maps to the real glyph 'foo'. Macro and request arguments preserve compatibility mode enablement. .cp 1 \" switch to compatibility mode .de xx \\$1 .. .cp 0 \" switch compatibility mode off .xx caf\['e] => café Since compatibility mode is enabled while 'de' is invoked, the macro 'xx' enables compatibility mode when it is called. Argument '$1' can still be handled properly because it inherits the compatibility mode enablement status that was active at the point where 'xx' was called. After interpolation of the parameters, the compatibility save and restore tokens are removed.  File: groff.info, Node: Gtroff Internals-Footnotes, Up: Gtroff Internals (1) Except the escape sequences '\f', '\F', '\H', '\m', '\M', '\R', '\s', and '\S', which are processed immediately if not in copy mode.  File: groff.info, Node: Debugging, Next: Implementation Differences, Prev: Gtroff Internals, Up: GNU troff Reference 5.37 Debugging ============== Standard troff voodoo, just put a power of two backslashes in front of it until it works and if you still have problems add a \c. -- Ron Natalie GNU 'troff' is not the easiest language to debug, in part thanks to its design features of recursive interpolation and the use of multi-stage pipeline processing in the surrounding system. Nevertheless there exist several features useful for troubleshooting. Preprocessors use the 'lf' request to preserve the identity of the line numbers and names of input files. GNU 'troff' emits a variety of error diagnostics and supports several categories of warning; the output of these can be selectively suppressed. A trace of the formatter's input processing stack can be emitted when errors or warnings occur by means of GNU 'troff''s '-b' option, or produced on demand with the 'backtrace' request. The 'tm' and related requests can be used to emit customized diagnostic messages or for instrumentation while troubleshooting. The 'ex' and 'ab' requests cause early termination with successful and error exit codes respectively, to halt further processing when continuing would be fruitless. Examine the state of the formatter with requests that write lists of defined names (macros, strings, and diversions), environments, registers, and page location traps to the standard error stream. -- Request: .lf line [file] Set the input line number (and, optionally, the file name) GNU 'troff' shall use for error and warning messages. LINE is the input line number of the _next_ line. Without an argument, the request is ignored. 'lf''s primary purpose is to aid the debugging of documents that undergo preprocessing. Programs like 'tbl' that transform input in their own languages into 'roff' requests use it so that any diagnostic messages emitted by 'troff' correspond to the source document. -- Request: .tm message -- Request: .tm1 message -- Request: .tmc message Send MESSAGE, which consumes the remainder of the input line and cannot contain special characters, to the standard error stream, followed by a newline. Leading spaces in MESSAGE are ignored. 'tm1' is similar, but recognizes and strips a leading neutral double quote from MESSAGE to allow the embedding of leading spaces. 'tmc' works as 'tm1', but does not append a newline. -- Request: .ab [message] Write any MESSAGE to the standard error stream (like 'tm') and then abort GNU 'troff'; that is, stop processing and terminate with a failure status. -- Request: .ex Exit GNU 'troff'; that is, stop processing and terminate with a successful status. To stop processing only the current file, use the 'nx' request; see *note I/O::. When doing something involved, it is useful to leave the debugging statements in the code and have them turned on by a command-line flag. .if \n[DB] .tm debugging output To activate such statements, use the '-r' option to set the register. groff -rDB=1 file If it is known in advance that there are many errors and no useful output, GNU 'troff' can be forced to suppress formatted output with the '-z' option. -- Request: .pev Report the state of the current environment followed by that of all other environments to the standard error stream. -- Request: .pm Report, to the standard error stream, the names of all defined macros, strings, and diversions with their sizes in bytes. -- Request: .pnr Report the names and contents of all currently defined registers to the standard error stream. -- Request: .ptr Report the names and positions of all page location traps to the standard error stream. Empty slots in the list, where a trap has been planted but subsequently (re)moved, are printed as well. -- Request: .fl Instruct 'gtroff' to flush its output immediately. The intent is for interactive use, but this behaviour is currently not implemented in 'gtroff'. Contrary to Unix 'troff', TTY output is sent to a device driver also ('grotty'), making it non-trivial to communicate interactively. This request causes a line break. -- Request: .backtrace Write the state of the input stack to the standard error stream. Consider the following in a file 'test'. .de xxx . backtrace .. .de yyy . xxx .. . .yyy error-> troff: backtrace: 'test':2: macro 'xxx' error-> troff: backtrace: 'test':5: macro 'yyy' error-> troff: backtrace: file 'test':8 The '-b' option of GNU 'troff' causes a backtrace to be generated on each error or warning. Some warnings have to be enabled; *Note Warnings::. -- Register: \n[slimit] If greater than 0, sets the maximum quantity of objects on GNU 'troff''s internal input stack. If less than or equal to 0, there is no limit: recursion can continue until program memory is exhausted. The default is 1,000. -- Request: .warnscale su Set the scaling unit used in certain warnings to SU, which can take the values 'u', 'i', 'c', 'p', and 'P'. The default is 'i'. -- Request: .spreadwarn [limit] Emit a 'break' warning if the additional space inserted for each space between words in an output line adjusted to both margins with '.ad b' is larger than or equal to LIMIT. A negative value is treated as zero; an absent argument toggles the warning on and off without changing LIMIT. The default scaling unit is 'm'. At startup, 'spreadwarn' is inactive and LIMIT is 3m. For example, .spreadwarn 0.2m causes a warning if 'break' warnings are not suppressed and 'gtroff' must add 0.2m or more for each inter-word space in a line. *Note Warnings::. GNU 'troff' has command-line options for reporting warnings ('-w') and backtraces ('-b') when a warning or an error occurs. -- Request: .warn [n] -- Register: \n[.warn] Select the categories, or "types", of reported warnings. N is the sum of the numeric codes associated with each warning category that is to be enabled; all other categories are disabled. The categories and their associated codes are listed in *note Warnings::. For example, '.warn 0' disables all warnings, and '.warn 1' disables all warnings except those about missing glyphs. If no argument is given, all warning categories are enabled. The read-only register '.warn' contains the sum of the numeric codes of enabled warning categories. * Menu: * Warnings::  File: groff.info, Node: Warnings, Prev: Debugging, Up: Debugging 5.37.1 Warnings --------------- Warning diagnostics emitted by GNU 'troff' are divided into named, numbered categories. The name associated with each warning category is used by the '-w' and '-W' options. Each category is also assigned a power of two; the sum of enabled category values is used by the 'warn' request and the '.warn' register. Warnings of each category are produced under the following circumstances. 'char' '1' No mounted font defines a glyph for the requested character. This category is enabled by default. 'number' '2' An invalid numeric expression was encountered. This category is enabled by default. *Note Numeric Expressions::. 'break' '4' A filled output line could not be broken such that its length was less than the output line length '\n[.l]'. This category is enabled by default. 'delim' '8' The closing delimiter in an escape sequence was missing or mismatched. 'el' '16' The 'el' request was encountered with no prior corresponding 'ie' request. *Note if-else::. 'scale' '32' A scaling unit inappropriate to its context was used in a numeric expression. 'range' '64' A numeric expression was out of range for its context. 'syntax' '128' A self-contradictory hyphenation mode was requested; an empty or incomplete numeric expression was encountered; an operand to a numeric operator was missing; an attempt was made to define a recursive, empty, or nonsensical character class; or a 'groff' extension conditional expression operator was used while in compatibility mode. 'di' '256' A 'di', 'da', 'box', or 'boxa' request was invoked without an argument when there was no current diversion. 'mac' '512' An undefined string, macro, or diversion was used. When such an object is dereferenced, an empty one of that name is automatically created. So, unless it is later deleted, at most one warning is given for each. This warning is also emitted upon an attempt to move an unplanted trap macro (*note Page Location Traps::). In such cases, the unplanted macro is _not_ dereferenced, so it is not created if it does not exist. 'reg' '1024' An undefined register was used. When an undefined register is dereferenced, it is automatically defined with a value of 0. So, unless it is later deleted, at most one warning is given for each. 'tab' '2048' A tab character was encountered where a number was expected, or appeared in an unquoted macro argument. 'right-brace' '4096' A right brace escape sequence '\}' was encountered where a number was expected. 'missing' '8192' A request was invoked with a mandatory argument absent. 'input' '16384' An invalid character occurred on the input stream. 'escape' '32768' An unsupported escape sequence was encountered. 'space' '65536' A space was missing between a request or macro and its argument. This warning is produced when an undefined name longer than two characters is encountered and the first two characters of the name constitute a defined name. No request is invoked, no macro called, and an empty macro is not defined. This category is enabled by default. It never occurs in compatibility mode. 'font' '131072' A non-existent font was selected, or the selection was ignored because a font selection escape sequence was used after the output line continuation escape sequence on an input line. This category is enabled by default. 'ig' '262144' An invalid escape sequence occurred in input ignored using the 'ig' request. This warning category diagnoses a condition that is an error when it occurs in non-ignored input. 'color' '524288' An undefined color was selected, an attempt was made to define a color using an unrecognized color space, an invalid component in a color definition was encountered, or an attempt was made to redefine a default color. 'file' '1048576' An attempt was made to load a file that does not exist. This category is enabled by default. Two warning names group other warning categories for convenience. 'all' All warning categories except 'di', 'mac' and 'reg'. This shorthand is intended to produce all warnings that are useful with macro packages written for AT&T 'troff' and its descendants, which have less fastidious diagnostics than GNU 'troff'. 'w' All warning categories. Authors of documents and macro packages targeting 'groff' are encouraged to use this setting.  File: groff.info, Node: Implementation Differences, Next: Safer Mode, Prev: Debugging, Up: GNU troff Reference 5.38 Implementation Differences =============================== GNU 'troff' has a number of features that cause incompatibilities with documents written for other versions of 'troff'. Some GNU extensions to 'troff' have become supported by other implementations. * Menu: * Safer Mode:: * Compatibility Mode:: * Other Differences::  File: groff.info, Node: Safer Mode, Next: Compatibility Mode, Prev: Implementation Differences, Up: Implementation Differences 5.38.1 Safer Mode ----------------- The formatter operates in "safer" mode by default; to mitigate risks from untrusted input documents, the 'pi' and 'sy' requests are disabled. GNU 'troff''s '-U' option enables "unsafe mode", restoring their function and enabling additional 'groff' extension requests, 'open', 'opena', and 'pso'. *Note I/O::.  File: groff.info, Node: Compatibility Mode, Next: Safer Mode, Prev: Other Differences, Up: Implementation Differences 5.38.2 Compatibility Mode ------------------------- Long identifier names may be GNU 'troff''s most obvious innovation. AT&T 'troff' interprets '.dsabcd' as defining a string 'ab' with contents 'cd'. Normally, GNU 'troff' interprets this as a call of a macro named 'dsabcd'. AT&T 'troff' also interprets '\*[' and '\n[' as an interpolation of a string or register, respectively, named '['. In GNU 'troff', however, the '[' is normally interpreted as delimiting a long name. In compatibility mode, GNU 'troff' interprets names in the traditional way; they thus can be two characters long at most. -- Request: .cp [n] -- Register: \n[.C] If N is missing or non-zero, turn on compatibility mode; otherwise, turn it off. The read-only register '.C' is 1 if compatibility mode is on, 0 otherwise. Compatibility mode can be also turned on with the '-C' command-line option. -- Request: .do name -- Register: \n[.cp] The 'do' request interprets the string, request, diversion, or macro NAME (along with any further arguments) with compatibility mode disabled. Compatibility mode is restored (only if it was active) when the _expansion_ of NAME is interpreted; that is, the restored compatibility state applies to the contents of the macro, string, or diversion NAME as well as data read from files or pipes if NAME is any of the 'so', 'soquiet', 'mso', 'msoquiet', or 'pso' requests. The following example illustrates several aspects of 'do' behavior. .de mac1 FOO .. .de1 mac2 groff .mac1 .. .de mac3 compatibility .mac1 .. .de ma \\$1 .. .cp 1 .do mac1 .do mac2 \" mac2, defined with .de1, calls "mac1" .do mac3 \" mac3 calls "ma" with argument "c1" .do mac3 \[ti] \" groff syntax accepted in .do arguments => FOO groff FOO compatibility c1 ~ The read-only register '.cp', meaningful only when dereferenced from a 'do' request, is 1 if compatibility mode was on when the 'do' request was encountered, and 0 if it was not. This register is specialized and may require a statement of rationale. When writing macro packages or documents that use GNU 'troff' features and which may be mixed with other packages or documents that do not--common scenarios include serial processing of man pages or use of the 'so' or 'mso' requests--you may desire correct operation regardless of compatibility mode enablement in the surrounding context. It may occur to you to save the existing value of '\n(.C' into a register, say, '_C', at the beginning of your file, turn compatibility mode off with '.cp 0', then restore it from that register at the end with '.cp \n(_C'. At the same time, a modular design of a document or macro package may lead you to multiple layers of inclusion. You cannot use the same register name everywhere lest you "clobber" the value from a preceding or enclosing context. The two-character register name space of AT&T 'troff' is confining and mnemonically challenging; you may wish to use the more capacious name space of GNU 'troff'. However, attempting '.nr _my_saved_C \n(.C' will not work in compatibility mode; the register name is too long. "This is exactly what 'do' is for," you think, '.do nr _my_saved_C \n(.C'. The foregoing will always save zero to your register, because 'do' turns compatibility mode _off_ while it interprets its argument list. To robustly save compatibility mode before switching it off, use .do nr _my_saved_C \n[.cp] .cp 0 at the beginning of your file, followed by .cp \n[_my_saved_C] .do rr _my_saved_C at the end. As in the C language, we all have to share one big name space, so choose a register name that is unlikely to collide with other uses. Normally, GNU 'troff' preserves the interpolation depth in delimited arguments, but not in compatibility mode. .ds xx ' \w'abc\*(xxdef' => 168 (normal mode on a terminal device) => 72def' (compatibility mode on a terminal device) Furthermore, the escape sequences '\f', '\H', '\m', '\M', '\R', '\s', and '\S' are transparent for the purpose of recognizing a control character at the beginning of a line only in compatibility mode. For example, this code produces bold output in both cases, but the text differs. .de xx Hello! .. \fB.xx\fP => .xx (normal mode) => Hello! (compatibility mode) Normally, the syntax form '\s'N accepts only a single character (a digit) for N, consistently with other forms that originated in AT&T 'troff', like '\*', '\$', '\f', '\g', '\k', '\n', and '\z'. In compatibility mode only, a non-zero N must be in the range 4-39. Legacy documents relying upon this quirk of parsing(1) (*note Compatibility Mode-Footnote-1::) should be migrated to another '\s' form.  File: groff.info, Node: Compatibility Mode-Footnotes, Up: Compatibility Mode (1) The Graphic Systems C/A/T phototypesetter (the original device target for AT&T 'troff') supported only a few discrete type sizes in the range 6-36 points, so Ossanna contrived a special case in the parser to do what the user must have meant. Kernighan warned of this in the 1992 revision of CSTR #54 (§2.3), and more recently, McIlroy referred to it as a "living fossil".  File: groff.info, Node: Other Differences, Prev: Compatibility Mode, Up: Implementation Differences 5.38.3 Other Differences ------------------------ 'groff' request names unrecognized by other 'troff' implementations will likely be ignored by them; escape sequences that are 'groff' extensions are liable to be interpreted as if the escape character were not present. For example, the adjustable, non-breaking escape sequence '\~' is also supported by Heirloom Doctools 'troff' 050915 (September 2005), 'mandoc' 1.9.5 (2009-09-21), 'neatroff' (commit 1c6ab0f6e, 2016-09-13), and Plan 9 from User Space 'troff' (commit 93f8143600, 2022-08-12), but not by Solaris or Documenter's Workbench 'troff's. *Note Manipulating Filling and Adjustment::. GNU 'troff' does not allow the use of the escape sequences '\|', '\^', '\&', '\{', '\}', '\', '\'', '\`', '\-', '\_', '\!', '\%', and '\c' in identifiers; AT&T 'troff' does. The '\A' escape sequence (*note Identifiers::) may be helpful in avoiding use of these escape sequences in names. When adjusting to both margins, AT&T 'troff' at first adjusts spaces starting from the right; GNU 'troff' begins from the left. Both implementations adjust spaces from opposite ends on alternating output lines in this adjustment mode to prevent "rivers" in the text. GNU 'troff' does not always hyphenate words as AT&T 'troff' does. The AT&T implementation uses a set of hard-coded rules specific to English, while GNU 'troff' uses language-specific hyphenation pattern files derived from TeX. Furthermore, in old versions of 'troff' there was a limited amount of space to store hyphenation exceptions (arguments to the 'hw' request); GNU 'troff' has no such restriction. GNU 'troff' predefines a string '.T' containing the argument given to the '-T' command-line option, namely the current output device (for example, 'pdf' or 'utf8'). The existence of this string is a common feature of post-CSTR #54 'troff's(1) (*note Other Differences-Footnote-1::) but valid values are specific to each implementation. AT&T 'troff' ignored attempts to remove read-only registers; GNU 'troff' honors such requests. *Note Built-in Registers::. The (read-only) register '.T' interpolates 1 if GNU 'troff' is called with the '-T' command-line option, and 0 otherwise. This behavior differs from AT&T 'troff', which interpolated 1 only if 'nroff' was the formatter and was called with '-T'. AT&T 'troff' and other implementations handle the 'lf' request differently. For them, its LINE argument changes the line number of the _current_ line. AT&T 'troff' had only environments named '0', '1', and '2'. In GNU 'troff', any number of environments may exist, using any valid identifiers for their names (*note Identifiers::.) Fractional type sizes cause one noteworthy incompatibility. In AT&T 'troff' the 'ps' request ignores scaling units and thus '.ps 10u' sets the type size to 10 points, whereas in GNU 'troff' it sets the type size to 10 _scaled_ points. *Note Using Fractional Type Sizes::. The 'ab' request differs from AT&T 'troff': GNU 'troff' writes no message to the standard error stream if no arguments are given, and it exits with a failure status instead of a successful one. The 'bp' request differs from AT&T 'troff': GNU 'troff' does not accept a scaling unit on the argument, a page number; the former (somewhat uselessly) does. The 'pm' request differs from AT&T 'troff': GNU 'troff' reports the sizes of macros, strings, and diversions in bytes and ignores an argument to report only the sum of the sizes. Unlike AT&T 'troff', GNU 'troff' does not ignore the 'ss' request if the output is a terminal device; instead, the values of minimal inter-word and additional inter-sentence space are each rounded down to the nearest multiple of 12. In GNU 'troff' there is a fundamental difference between (unformatted) characters and (formatted) glyphs. Everything that affects how a glyph is output is stored with the glyph node; once a glyph node has been constructed, it is unaffected by any subsequent requests that are executed, including 'bd', 'cs', 'tkf', 'tr', or 'fp' requests. Normally, glyphs are constructed from characters immediately before the glyph is added to an output line. Macros, diversions, and strings are all, in fact, the same type of object; they contain a sequence of intermixed character and glyph nodes. Special characters transform from one to the other: before being added to the output, they behave as characters; afterward, they are glyphs. A glyph node does not behave like a character node when it is processed by a macro: it does not inherit any of the special properties that the character from which it was constructed might have had. For example, the input .di x \\\\ .br .di .x produces '\\' in GNU 'troff'. Each pair of backslashes becomes one backslash _glyph_; the resulting backslashes are thus not interpreted as escape _characters_ when they are reread as the diversion is output. AT&T 'troff' _would_ interpret them as escape characters when rereading them and end up printing one '\'. One correct way to obtain a printable backslash in most documents is to use the '\e' escape sequence; this always prints a single instance of the current escape character,(2) (*note Other Differences-Footnote-2::) regardless of whether or not it is used in a diversion; it also works in both GNU 'troff' and AT&T 'troff'. The other correct way, appropriate in contexts independent of the backslash's common use as a 'troff' escape character--perhaps in discussion of character sets or other programming languages--is the character escape '\(rs' or '\[rs]', for "reverse solidus", from its name in the ECMA-6 (ISO/IEC 646) standard.(3) (*note Other Differences-Footnote-3::) To store an escape sequence in a diversion that is interpreted when the diversion is reread, either use the traditional '\!' transparent output facility, or, if this is unsuitable, the new '\?' escape sequence. *Note Diversions:: and *note Gtroff Internals::. In the somewhat pathological case where a diversion exists containing a partially collected line and a partially collected line at the top-level diversion has never existed, AT&T 'troff' will output the partially collected line at the end of input; GNU 'troff' will not.  File: groff.info, Node: Other Differences-Footnotes, Up: Other Differences (1) DWB 3.3, Solaris, Heirloom Doctools, and Plan 9 'troff' all support it. (2) Naturally, if you've changed the escape character, you need to prefix the 'e' with whatever it is--and you'll likely get something other than a backslash in the output. (3) The 'rs' special character identifier was not defined in AT&T 'troff''s font description files, but is in those of its lineal descendant, Heirloom Doctools 'troff', as of the latter's 060716 release (July 2006).  File: groff.info, Node: File Formats, Next: Copying This Manual, Prev: GNU troff Reference, Up: Top 6 File Formats ************** All files read and written by 'gtroff' are text files. The following two sections describe their format. * Menu: * gtroff Output:: * Device and Font Description Files::  File: groff.info, Node: gtroff Output, Next: Device and Font Description Files, Prev: File Formats, Up: File Formats 6.1 'gtroff' Output =================== This section describes the 'groff' intermediate output format produced by GNU 'troff'. As 'groff' is a wrapper program around GNU 'troff' and automatically calls an output driver (or "postprocessor"), this output does not show up normally. This is why it is called _intermediate_. 'groff' provides the option '-Z' to inhibit postprocessing such that the produced intermediate output is sent to standard output just as it is when calling GNU 'troff' directly. Here, the term "troff output" describes what is output by GNU 'troff', while "intermediate output" refers to the language that is accepted by the parser that prepares this output for the output drivers. This parser handles whitespace more flexibly than AT&T's implementation and implements obsolete elements for compatibility; otherwise, both formats are the same.(1) (*note gtroff Output-Footnote-1::) The main purpose of the intermediate output concept is to facilitate the development of postprocessors by providing a common programming interface for all devices. It has a language of its own that is completely different from the 'gtroff' language. While the 'gtroff' language is a high-level programming language for text processing, the intermediate output language is a kind of low-level assembler language by specifying all positions on the page for writing and drawing. The intermediate output produced by 'gtroff' is fairly readable, while output from AT&T 'troff' is rather hard to understand because of strange habits that are still supported, but not used any longer by 'gtroff'. * Menu: * Language Concepts:: * Command Reference:: * Intermediate Output Examples:: * Output Language Compatibility::  File: groff.info, Node: gtroff Output-Footnotes, Up: gtroff Output (1) The parser and postprocessor for intermediate output can be found in the file 'GROFF-SOURCE-DIR/src/libs/libdriver/input.cpp'.  File: groff.info, Node: Language Concepts, Next: Command Reference, Prev: gtroff Output, Up: gtroff Output 6.1.1 Language Concepts ----------------------- The fundamental operation of the GNU 'troff' formatter is the translation of the 'groff' input language into a device-independent form primarily concerned with what has to be written or drawn at specific positions on the output device. This language is simple and imperative. In the following discussion, the term "command" always refers to this intermediate output language, and never to the 'groff' language intended for direct use by document authors. Intermediate output commands comprise several categories: glyph output; font, color, and text size selection; motion of the printing position; page advancement; drawing of geometric objects; and device control commands, a catch-all for operations not easily classified as any of the foregoing, such as directives to start and stop output, identify the intended output device, or place URL hyperlinks in supported output formats. * Menu: * Separation:: * Argument Units:: * Document Parts::  File: groff.info, Node: Separation, Next: Argument Units, Prev: Language Concepts, Up: Language Concepts 6.1.1.1 Separation .................. AT&T 'troff' output has strange requirements regarding whitespace. The 'gtroff' output parser, however, is more tolerant, making whitespace maximally optional. Such characters, i.e., the tab, space, and newline, 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 separates 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 arguments 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 whitespace, a comment, or a newline character. Thus a "syntactical line break" is defined to consist 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 commands on the same line, but fortunately, in 'gtroff''s 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 span several input 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. Empty lines (these are lines containing only space and/or a comment), can occur everywhere. They are just ignored.  File: groff.info, Node: Argument Units, Next: Document Parts, Prev: Separation, Up: Language Concepts 6.1.1.2 Argument Units ...................... Some commands take integer arguments that are assumed to represent values in a measurement unit, but the letter for the corresponding scaling unit is not written with the output command arguments. Most commands assume the scaling unit 'u', the basic unit of the device, some use 'z', the scaled point unit of the device, while others, such as the color commands, expect plain integers. Single characters can have the eighth bit set, as can the names of fonts and special characters. The names of characters and fonts can be of arbitrary length. A character that is to be printed is always in the current font. A string argument is always terminated by the next whitespace character (space, tab, or newline); 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.  File: groff.info, Node: Document Parts, Prev: Argument Units, Up: Language Concepts 6.1.1.3 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 specified commands. 'gtroff''s 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 *note Device Control Commands::. The parser for the intermediate output format is able to interpret additional whitespace and comments as well even in the prologue. The body is the main section for processing the document data. Syntactically, it is a sequence of any commands different from the ones used in the prologue. Processing is terminated as soon as the first 'x stop' command is encountered; the last line of any 'gtroff' intermediate 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.  File: groff.info, Node: Command Reference, Next: Intermediate Output Examples, Prev: Language Concepts, Up: gtroff Output 6.1.2 Command Reference ----------------------- This section describes all intermediate output commands, both from AT&T 'troff' as well as the 'gtroff' extensions. * Menu: * Comment Command:: * Simple Commands:: * Graphics Commands:: * Device Control Commands:: * Obsolete Command::  File: groff.info, Node: Comment Command, Next: Simple Commands, Prev: Command Reference, Up: Command Reference 6.1.2.1 Comment Command ....................... '#ANYTHING' A comment. Ignore any characters from the '#' character up to the next newline character. This command is the only possibility for commenting in the intermediate output. Each comment can be preceded by arbitrary syntactical space; every command can be terminated by a comment.  File: groff.info, Node: Simple Commands, Next: Graphics Commands, Prev: Comment Command, Up: Command Reference 6.1.2.2 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 tolerant of whitespace. Optionally, syntactical space can be inserted before, 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' Typeset the glyph of the special character ID. Trailing syntactical space is necessary to allow special character names of arbitrary length. The drawing position is not advanced. 'c G' Typeset the glyph of the ordinary 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 COLOR-SCHEME [COMPONENT ...]' Select the stroke color using the COMPONENTs in the color space SCHEME. Each COMPONENT is an integer between 0 and 65535. 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 65535 (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 integer. 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' below. '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 *note Output Language Compatibility::. 't XYZ' 't XYZ DUMMY-ARG' Typeset a word XYZ; that is, set a sequence of ordinary glyphs named X, Y, Z, ..., terminated by a space character or a line break; 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 *note DESC File Format::. 'u N XYZ' Typeset word XYZ with track kerning. As 't', but after placing each glyph, the drawing position is further advanced horizontally by N basic units ('u'). The 'u' command is a 'groff' extension and is output only for devices whose 'DESC' file contains the 'tcommand' directive; see *note DESC File Format::. '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' above.  File: groff.info, Node: Graphics Commands, Next: Device Control Commands, Prev: Simple Commands, Up: Command Reference 6.1.2.3 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. 'gtroff' 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 integers representing a size measured in basic units 'u'. The arguments called H1, H2, ..., HN stand for horizontal distances where positive means right, negative left. The arguments called V1, V2, ..., VN stand for vertical distances where positive means down, negative up. All these distances are offsets relative to the current location. Each graphics command directly corresponds to a similar 'gtroff' '\D' escape sequence. *Note Drawing Geometric Objects::. 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 means a syntactical line break as defined above. 'D~ H1 V1 H2 V2 ... HN VN' 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' 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' 'DC D DUMMY-ARG' 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 'gtroff' extension. 'Dc D' 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' 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 'gtroff' extension. 'De H V' 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 ...]' 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 objects is 'm'. The color components are specified as integer arguments between 0 and 65535. The number of color components and their meaning vary for the different color schemes. These commands are generated by 'gtroff''s escape sequences '\D'F ...'' and '\M' (with no other corresponding graphics commands). No position changing. This command is a 'gtroff' extension. 'DFc CYAN MAGENTA YELLOW' Set fill color for solid drawing objects using the CMY color scheme, having the 3 color components CYAN, MAGENTA, and YELLOW. 'DFd' Set fill color for solid drawing objects to the default fill color value (black in most cases). No component arguments. 'DFg GRAY' Set fill color for solid drawing objects to the shade of gray given by the argument, an integer between 0 (black) and 65535 (white). 'DFk CYAN MAGENTA YELLOW BLACK' 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' Set fill color for solid drawing objects using the RGB color scheme, having the 3 color components RED, GREEN, and BLUE. 'Df N' 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 65535 Df -1 sets all colors to blue. No position changing. This command is a 'gtroff' extension. 'Dl H V' 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' 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 actual horizontal position and the even ones to the vertical position. Although this doesn't make sense it is kept for compatibility. This command is a 'gtroff' extension. 'DP H1 V1 H2 V2 ... HN VN' Draw a solid polygon in the current fill color rather than an outlined polygon, using the same arguments and positioning as the corresponding 'Dp' command. This command is a 'gtroff' extension. 'Dt N' Set the current line thickness to N (an integer in basic units 'u') if N>0; if N=0 select the smallest available line thickness; if N<0 set the line thickness proportional to the type size (this is the default before the first 'Dt' command was specified). For historical reasons, the horizontal position is changed by adding the argument to the actual horizontal position, while the vertical position is not changed. Although this doesn't make sense it is kept for compatibility. This command is a 'gtroff' extension.  File: groff.info, Node: Device Control Commands, Next: Obsolete Command, Prev: Graphics Commands, Up: Command Reference 6.1.2.4 Device Control Commands ............................... Each device control command starts with the letter 'x', followed by a space character (optional or arbitrary space or tab in 'gtroff') 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, 'gtroff' outputs the initialization command 'x i' as 'x init' and the resolution command 'x r' as 'x res'. In the following, the syntax element means a syntactical line break (*note Separation::). 'xF NAME' The 'F' stands for FILENAME. Use NAME as the intended name for the current file in error reports. This is useful for remembering the original file name when 'gtroff' uses an internal piping mechanism. The input file is not changed by this command. This command is a 'gtroff' extension. 'xf N S' The 'f' stands for FONT. Mount font position N (a non-negative integer) with font named S (a text word). *Note Font Positions::. 'xH N' The 'H' stands for HEIGHT. Set glyph height to N (a positive integer in scaled points 'z'). AT&T 'troff' uses the unit points ('p') instead. *Note Output Language Compatibility::. 'xi' The 'i' stands for INIT. Initialize device. This is the third command of the prologue. 'xp' The 'p' stands for PAUSE. Parsed but ignored. The AT&T 'troff' manual documents this command as pause device, can be restarted but GNU 'troff' output drivers do nothing with this command. 'xr N H V' The 'r' stands for RESOLUTION. 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' The 'S' stands for SLANT. Set slant to N (an integer in basic units 'u'). 'xs' The 's' stands for STOP. Terminates the processing of the current file; issued as the last command of any intermediate 'troff' output. 'xt' The 't' stands for TRAILER. Generate trailer information, if any. In GNU 'troff', this is ignored. 'xT XXX' The 'T' stands for TYPESETTER. Set the name of the output driver to XXX, a sequence of non-whitespace characters terminated by whitespace. The possible names correspond to those of 'groff''s '-T' option. This is the first command of the prologue. 'xu N' The 'u' stands for UNDERLINE. 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 'gtroff' extension. 'xX ANYTHING' The 'x' stands for X-ESCAPE. 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 following sense. The '+' is ignored, but a newline character is sent instead to the device, 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 generated by the 'gtroff' escape sequence '\X'. The line-continuing feature is a 'gtroff' extension.  File: groff.info, Node: Obsolete Command, Prev: Device Control Commands, Up: Command Reference 6.1.2.5 Obsolete Command ........................ In AT&T 'troff' output, the writing of a single glyph is mostly done by a very strange command that combines a horizontal move and a single character giving the glyph name. It doesn't have a command code, but is represented by a 3-character argument consisting of exactly 2 digits and a character. DDG Move right DD (exactly two decimal digits) basic units 'u', then print glyph G (represented as a single character). In GNU 'troff', arbitrary syntactical space around and within this command is allowed. Only when a preceding command on the same line ends with an argument of variable length is a separating space obligatory. In AT&T 'troff', large clusters of these and other commands are used, mostly without spaces; this made such output almost 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 'gtroff', this is only used for the devices 'X75', 'X75-12', 'X100', and 'X100-12'. For other devices, the commands 't' and 'u' provide a better functionality.  File: groff.info, Node: Intermediate Output Examples, Next: Output Language Compatibility, Prev: Command Reference, Up: gtroff Output 6.1.3 Intermediate Output Examples ---------------------------------- This section presents the intermediate output generated from the same input for three different devices. The input is the sentence 'hell world' fed into 'gtroff' on the command line. High-resolution device 'ps' This is the standard output of 'gtroff' if no '-T' option is given. 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 'grops' to get its representation as a PostScript file. Low-resolution device 'latin1' This is similar to the high-resolution device except that the positioning is done at a minor scale. Some comments (lines starting with '#') were added for clarification; they were not generated by the formatter. shell> echo "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 space, and issue 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 'grotty' to get a formatted text document. AT&T 'troff' output Since a computer monitor has a much lower resolution than modern printers, the intermediate output for X11 devices can use the jump-and-write command with its 2-digit displacements. shell> echo "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 jump-and-write commands ch07e07l03lw06w11o07r05l03dh7 n16 0 x trailer V1100 x stop This output can be fed into 'xditview' or 'gxditview' for displaying in X. Due to the obsolete jump-and-write command, the text clusters in the AT&T 'troff' output are almost unreadable.  File: groff.info, Node: Output Language Compatibility, Prev: Intermediate Output Examples, Up: gtroff Output 6.1.4 Output Language Compatibility ----------------------------------- The intermediate output language of AT&T 'troff' was first documented in 'A Typesetter-independent TROFF', by Brian Kernighan, and by 1992 the AT&T 'troff' manual was updated to incorprate a description of it. The GNU 'troff' 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 AT&T 'troff'. For example, the AT&T PostScript device is called 'post' and has a resolution of only 720 units per inch, suitable for printers 20 years ago, 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, 'groff' could emulate AT&T's 'post' device. * 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 'gtroff', while AT&T 'troff' has point ('p'). This isn't an incompatibility but a compatible extension, for both units coincide for all devices without a 'sizescale' parameter in the 'DESC' file, including all postprocessors from AT&T and 'groff''s text devices. The few 'groff' devices with a 'sizescale' parameter either do not exist for AT&T 'troff', have a different name, or seem to have a different resolution. So conflicts are very unlikely. * The position changing after the commands 'Dp', 'DP', and 'Dt' is illogical, but as old versions of 'gtroff' used this feature it is kept for compatibility reasons.  File: groff.info, Node: Device and Font Description Files, Prev: gtroff Output, Up: File Formats 6.2 Device and Font Description Files ===================================== The 'groff' font and output device description formats are slight extensions of those used by AT&T device-independent 'troff'. In distinction to the AT&T implementation, 'groff' lacks a binary format; all files are text files.(1) (*note Device and Font Description Files-Footnote-1::) The device and font description files for a device NAME are stored in a 'devNAME' directory. The device description file is called 'DESC', and, for each font supported by the device, a font description file is called 'F', where F is usually an abbreviation of a font's name and/or style. For example, the 'ps' (PostScript) device has 'groff' font description files for Times roman ('TR') and Zapf Chancery Medium italic ('ZCMI'), among many others, while the 'utf8' device (for terminal emulators) has only font descriptions for the roman, italic, bold, and bold-italic styles ('R', 'I', 'B', and 'BI', respectively). Device and font description files are read both by the formatter, GNU 'troff', and by output drivers. The programs delegate these files' processing to an internal library, 'libgroff', ensuring their consistent interpretation. * Menu: * DESC File Format:: * Font Description File Format::  File: groff.info, Node: Device and Font Description Files-Footnotes, Up: Device and Font Description Files (1) Plan 9 'troff' has also abandoned the binary format.  File: groff.info, Node: DESC File Format, Next: Font Description File Format, Prev: Device and Font Description Files, Up: Device and Font Description Files 6.2.1 'DESC' File Format ------------------------ The 'DESC' file contains a series of directives; each begins a line. Their order is not important, with two exceptions: (1) the 'res' directive must precede any 'papersize' directive; and (2) the 'charset' directive must come last (if at all). If a directive name is repeated, later entries in the file override previous ones (except that the paper dimensions are computed based on the 'res' directive last seen when 'papersize' is encountered). Spaces and/or tabs separate words and are ignored at line boundaries. Comments start with the '#' character and extend to the end of a line. Empty lines are ignored. 'family FAM' The default font family is FAM. 'fonts N F1 ... FN' Fonts F1, ..., FN are mounted at font positions M+1, ..., M+N where M is the number of 'styles' (see below). This directive may extend over more than one line. A font name of '0' causes no font to be mounted at the corresponding position. 'hor N' The horizontal motion quantum is N basic units. All horizontal quantities are rounded to multiples of N. 'image_generator PROGRAM' Use PROGRAM to generate PNG images from PostScript input. Under GNU/Linux, this is usually 'gs', but under other systems (notably Cygwin) it might be set to another name. The 'grohtml' driver uses this directive. 'paperlength N' The vertical dimension of the output medium is N basic units (deprecated: use 'papersize' instead). 'papersize FORMAT-OR-DIMENSION-PAIR-OR-FILE-NAME ...' The dimensions of the output medium are as according to the argument, which is either a standard paper format, a pair of dimensions, or the name of a plain text file containing either of the foregoing. Recognized paper formats are the ISO and DIN formats 'A0'-'A7', 'B0'-'B7', 'C0'-'C7', 'D0'-'D7'; the U.S. paper types 'letter', 'legal', 'tabloid', 'ledger', 'statement', and 'executive'; and the envelope formats 'com10', 'monarch', and 'DL'. Matching is performed without regard for lettercase. Alternatively, the argument can be a custom paper format in the format 'LENGTH,WIDTH' (with no spaces before or after the comma). Both LENGTH and WIDTH must have a unit appended; valid units are 'i' for inches, 'c' for centimeters, 'p' for points, and 'P' for picas. Example: '12c,235p'. An argument that starts with a digit is always treated as a custom paper format. Finally, the argument can be a file name (e.g., '/etc/papersize'); if the file can be opened, the first line is read and a match attempted against each of the other forms. No comment syntax is supported. More than one argument can be specified; each is scanned in turn and the first valid paper specification used. 'paperwidth N' The horizontal dimension of the output medium is N basic units (deprecated: use 'papersize' instead). 'pass_filenames' Direct GNU 'troff' to emit the name of the source file being processed. This is achieved with the intermediate output command 'x F', which 'grohtml' interprets. 'postpro PROGRAM' Use PROGRAM as the postprocessor. 'prepro PROGRAM' Use PROGRAM as a preprocessor. The 'html' and 'xhtml' output devices use this directive. 'print PROGRAM' Use PROGRAM as a spooler program for printing. If omitted, the '-l' and '-L' options of 'groff' are ignored. 'res N' The device resolution is N basic units per inch. 'sizes S1 ... SN 0' The device has fonts at S1, ..., SN scaled points (see below). The list of sizes must be terminated by '0'. Each SI can also be a range of sizes M-N. The list can extend over more than one line. 'sizescale N' A typographical point is subdivided into N scaled points. The default is '1'. *Note Using Fractional Type Sizes::. 'styles S1 ... SM' The first M mounting positions are associated with styles S1, ..., SM. 'tcommand' The postprocessor can handle the 't' and 'u' intermediate output commands. 'unicode' The output device supports the complete Unicode repertoire. This directive is useful only for devices that produce character entities instead of glyphs. If 'unicode' is present, no 'charset' section is required in the font description files since the Unicode handling built into 'groff' is used. However, if there are entries in a font description file's 'charset' section, they either override the default mappings for those particular characters or add new mappings (normally for composite characters). The 'utf8', 'html', and 'xhtml' output devices use this directive. 'unitwidth N' Quantities in the font description files are in basic units for fonts whose type size is N scaled points. 'unscaled_charwidths' Make the font handling module always return unscaled character widths. The 'grohtml' driver uses this directive. 'use_charnames_in_special' GNU 'troff' should encode special characters inside device control commands; see *note Postprocessor Access::. The 'grohtml' driver uses this directive. 'vert N' The vertical motion quantum is N basic units. All vertical quantities are rounded to multiples of N. 'charset' This line and everything following it in the file are ignored. It is recognized for compatibility with other 'troff' implementations. In GNU 'troff', character set repertoire is described on a per-font basis. GNU 'troff' recognizes but ignores the directives 'spare1', 'spare2', and 'biggestfont'. The 'res', 'unitwidth', 'fonts', and 'sizes' lines are mandatory. Directives not listed above are ignored by GNU 'troff' but may be used by postprocessors to obtain further information about the device.  File: groff.info, Node: Font Description File Format, Prev: DESC File Format, Up: Device and Font Description Files 6.2.2 Font Description File Format ---------------------------------- On typesetting output devices, each font is typically available at multiple sizes. While paper measurements in the device description file are in absolute units, measurements applicable to fonts must be proportional to the type size. 'groff' achieves this using the precedent set by AT&T device-independent 'troff': one font size is chosen as a norm, and all others are scaled linearly relative to that basis. The "unit width" is the number of basic units per point when the font is rendered at this nominal size. For instance, 'groff''s 'lbp' device uses a 'unitwidth' of 800. Its Times roman font 'TR' has a 'spacewidth' of 833; this is also the width of its comma, period, centered period, and mathematical asterisk, while its 'M' is 2,963 basic units. Thus, an 'M' on the 'lbp' device is 2,963 basic units wide at a notional type size of 800 points.(1) (*note Font Description File Format-Footnote-1::) A font description file has two sections. The first is a sequence of directives, and is parsed similarly to the 'DESC' file described above. Except for the directive names that begin the second section, their ordering is immaterial. Later directives of the same name override earlier ones, spaces and tabs are handled in the same way, and the same comment syntax is supported. Empty lines are ignored throughout. 'name F' The name of the font is F. 'DESC' is an invalid font name. Simple integers are valid, but their use is discouraged.(2) (*note Font Description File Format-Footnote-2::) 'spacewidth N' The width of an unadjusted inter-word space is N basic units. The directives above must appear in the first section; those below are optional. 'slant N' The font's glyphs have a slant of N degrees; a positive N slants in the direction of text flow. 'ligatures LIG1 ... LIGN [0]' Glyphs LIG1, ..., LIGN are ligatures; possible ligatures are 'ff', 'fi', 'fl', 'ffi' and 'ffl'. For compatibility with other 'troff' implementations, the list of ligatures may be terminated with a '0'. The list of ligatures must not extend over more than one line. 'special' The font is "special": when a glyph is requested that is not present in the current font, it is sought in any mounted fonts that bear this property. Other directives in this section are ignored by GNU 'troff', but may be used by postprocessors to obtain further information about the font. The second section contains one or two subsections. These can appear in either order; the first one encountered commences the second section. Each starts with a directive on a line by itself. A 'charset' subsection is mandatory unless the associated 'DESC' file contains the 'unicode' directive. Another subsection, 'kernpairs', is optional. The directive 'charset' starts the character set subsection.(3) (*note Font Description File Format-Footnote-3::) It precedes a series of glyph descriptions, one per line. Each such glyph description comprises a set of fields separated by spaces or tabs and organized as follows. NAME METRICS TYPE CODE [ENTITY-NAME] ['--' COMMENT] NAME identifies the glyph: if NAME is a printable character C, it corresponds to the 'troff' ordinary character C. If NAME is a multi-character sequence not beginning with '\', it corresponds to the GNU 'troff' special character escape sequence '\[NAME]'. A name consisting of three minus signs, '---', is special and indicates that the glyph is unnamed: such glyphs can be accessed only by the '\N' escape sequence in 'troff'. A special character named '---' can still be defined using 'char' and similar requests. The NAME '\-' defines the minus sign glyph. Finally, NAME can be the unbreakable one-sixth and one-twelfth space escape sequences, '\|' and '\^' ("thin" and "hair" spaces, respectively), in which case only the width metric described below is interpreted; a font can thus customize the widths of these spaces. The form of the METRICS field is as follows. WIDTH[','[HEIGHT[','[DEPTH[','[ITALIC-CORRECTION [','[LEFT-ITALIC-CORRECTION[','[SUBSCRIPT-CORRECTION]]]]]]]]]] There must not be any spaces, tabs, or newlines between these "subfields" (which have been split here into two lines only for better legibility). The subfields are in basic units expressed as decimal integers. Unspecified subfields default to '0'. Since there is no associated binary format, these values are not required to fit into the C language data type 'char' as they are in AT&T device-independent 'troff'. The WIDTH subfield gives the width of the glyph. The HEIGHT subfield gives the height of the glyph (upward is positive); if a glyph does not extend above the baseline, it should be given a zero height, rather than a negative height. The DEPTH subfield gives the depth of the glyph, that is, the distance below the baseline to which the glyph extends (downward is positive); if a glyph does not extend below the baseline, it should be given a zero depth, rather than a negative depth. Italic corrections are relevant to glyphs in italic or oblique styles. The ITALIC-CORRECTION is the amount of space that should be added after an oblique glyph to be followed immediately by an upright glyph. The LEFT-ITALIC-CORRECTION is the amount of space that should be added before an oblique glyph to be preceded immediately by an upright glyph. The SUBSCRIPT-CORRECTION is the amount of space that should be added after an oblique glyph to be followed by a subscript; it should be less than the italic correction. For fonts used with typesetting devices, the TYPE field gives a featural description of the glyph: it is a bit mask recording whether the glyph is an ascender, descender, both, or neither. When a '\w' escape sequence is interpolated, these values are bitwise or-ed together for each glyph and stored in the 'nr' register. In font descriptions for terminal devices, all glyphs might have a type of zero, regardless of their appearance. '0' means the glyph lies entirely between the baseline and a horizontal line at the "x-height" of the font; typical examples are 'a', 'c', and 'x'; '1' means the glyph descends below the baseline, like 'p'; '2' means the glyph ascends above the font's x-height, like 'A' or 'b'; and '3' means the glyph is both an ascender and a descender--this is true of parentheses in some fonts. The CODE field gives a numeric identifier that the postprocessor uses to render the glyph. The glyph can be specified to 'troff' using this code by means of the '\N' escape sequence. CODE can be any integer.(4) (*note Font Description File Format-Footnote-4::) The ENTITY-NAME field defines an identifier for the glyph that the postprocessor uses to print the GNU 'troff' glyph NAME. This field is optional; it was introduced so that the 'grohtml' output driver could encode its character set. For example, the glyph '\[Po]' is represented by '£' in HTML 4.0. For efficiency, these data are now compiled directly into 'grohtml'. 'grops' uses the field to build sub-encoding arrays for PostScript fonts containing more than 256 glyphs. Anything on the line after the ENTITY-NAME field or '--' is ignored. A line in the 'charset' section can also have the form NAME " identifying NAME as another name for the glyph mentioned in the preceding line. Such aliases can be chained. The directive 'kernpairs' starts a list of kerning adjustments to be made to adjacent glyph pairs from this font. It contains a sequence of lines formatted as follows. G1 G2 N The foregoing means that when glyph G1 is typeset immediately before G2, the space between them should be increased by N. Most kerning pairs should have a negative value for N.  File: groff.info, Node: Font Description File Format-Footnotes, Up: Font Description File Format (1) 800-point type is not practical for most purposes, but using it enables the quantities in the font description files to be expressed as integers. (2) 'groff' requests and escape sequences interpret non-negative font names as mounting positions instead. Further, a font named '0' cannot be automatically mounted by the 'fonts' directive of a 'DESC' file. (3) For typesetter devices, this directive is misnamed since it starts a list of glyphs, not characters. (4) that is, any integer parsable by the C standard library's 'strtol(3)' function  File: groff.info, Node: Copying This Manual, Next: Request Index, Prev: Font Description File Format, Up: Top Appendix A Copying This Manual ****************************** Version 1.3, 3 November 2008 Copyright © 2000-2018 Free Software Foundation, Inc. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others. This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software. We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference. 1. APPLICABILITY AND DEFINITIONS This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". 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The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none. The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words. A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque". Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only. The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text. The "publisher" means any person or entity that distributes copies of the Document to the public. A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition. The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License. 2. VERBATIM COPYING You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3. You may also lend copies, under the same conditions stated above, and you may publicly display copies. 3. COPYING IN QUANTITY If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects. If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages. If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public. It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document. 4. MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version: A. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission. B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement. C. State on the Title page the name of the publisher of the Modified Version, as the publisher. D. Preserve all the copyright notices of the Document. E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices. F. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below. G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice. H. Include an unaltered copy of this License. I. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence. J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission. K. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein. L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles. M. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version. N. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section. O. Preserve any Warranty Disclaimers. If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles. You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard. You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one. The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version. 5. COMBINING DOCUMENTS You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers. The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work. In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements." 6. COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects. You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document. 7. AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document. If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate. 8. TRANSLATION Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail. If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title. 9. TERMINATION You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License. However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation. Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice. Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it. 10. FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See . Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document. 11. RELICENSING "Massive Multiauthor Collaboration Site" (or "MMC Site") means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A "Massive Multiauthor Collaboration" (or "MMC") contained in the site means any set of copyrightable works thus published on the MMC site. "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization. "Incorporate" means to publish or republish a Document, in whole or in part, as part of another Document. An MMC is "eligible for relicensing" if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008. The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing. ADDENDUM: How to use this License for your documents ==================================================== To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: Copyright (C) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts." line with this: with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.  File: groff.info, Node: Request Index, Next: Escape Sequence Index, Prev: Copying This Manual, Up: Top Appendix B Request Index ************************ Request names appear without a leading control character; the defaults are '.' for the regular control character and ''' for the no-break control character. [index] * Menu: * ab: Debugging. (line 55) * ad: Manipulating Filling and Adjustment. (line 83) * af: Assigning Register Formats. (line 12) * aln: Setting Registers. (line 110) * als: Strings. (line 198) * am: Writing Macros. (line 126) * am1: Writing Macros. (line 127) * ami: Writing Macros. (line 128) * ami1: Writing Macros. (line 129) * as: Strings. (line 114) * as1: Strings. (line 115) * asciify: Diversions. (line 208) * backtrace: Debugging. (line 104) * bd: Artificial Fonts. (line 95) * blm: Blank Line Traps. (line 7) * box: Diversions. (line 63) * boxa: Diversions. (line 64) * bp: Page Control. (line 11) * br: Manipulating Filling and Adjustment. (line 39) * break: while. (line 72) * brp: Manipulating Filling and Adjustment. (line 156) * c2: Control Characters. (line 29) * cc: Control Characters. (line 23) * ce: Manipulating Filling and Adjustment. (line 208) * cf: I/O. (line 58) * cflags: Using Symbols. (line 252) * ch: Page Location Traps. (line 114) * char: Using Symbols. (line 351) * chop: Strings. (line 145) * class: Character Classes. (line 12) * close: I/O. (line 240) * color: Colors. (line 15) * composite: Using Symbols. (line 208) * continue: while. (line 76) * cp: Compatibility Mode. (line 16) * cs: Artificial Fonts. (line 125) * cu: Artificial Fonts. (line 86) * da: Diversions. (line 32) * de: Writing Macros. (line 14) * de1: Writing Macros. (line 86) * defcolor: Colors. (line 27) * dei: Writing Macros. (line 108) * dei1: Writing Macros. (line 109) * device: Postprocessor Access. (line 15) * devicem: Postprocessor Access. (line 45) * di: Diversions. (line 31) * do: Compatibility Mode. (line 27) * ds: ms Document Control Settings. (line 15) * ds <1>: Strings. (line 24) * ds1: Strings. (line 25) * dt: Diversion Traps. (line 11) * ec: Using Escape Sequences. (line 76) * ecr: Using Escape Sequences. (line 102) * ecs: Using Escape Sequences. (line 101) * el: if-else. (line 8) * em: End-of-input Traps. (line 7) * eo: Using Escape Sequences. (line 71) * ev: Environments. (line 46) * evc: Environments. (line 100) * ex: Debugging. (line 60) * fam: Font Families. (line 21) * fc: Fields. (line 18) * fchar: Using Symbols. (line 352) * fcolor: Colors. (line 85) * fi: Manipulating Filling and Adjustment. (line 66) * fl: Debugging. (line 95) * fp: Font Positions. (line 16) * fschar: Using Symbols. (line 353) * fspecial: Special Fonts. (line 18) * ft: Selecting Fonts. (line 11) * ftr: Selecting Fonts. (line 69) * fzoom: Selecting Fonts. (line 83) * gcolor: Colors. (line 57) * hc: Manipulating Hyphenation. (line 88) * hcode: Manipulating Hyphenation. (line 293) * hla: Manipulating Hyphenation. (line 327) * hlm: Manipulating Hyphenation. (line 340) * hpf: Manipulating Hyphenation. (line 233) * hpfa: Manipulating Hyphenation. (line 234) * hpfcode: Manipulating Hyphenation. (line 235) * hw: Manipulating Hyphenation. (line 22) * hy: Manipulating Hyphenation. (line 120) * hym: Manipulating Hyphenation. (line 354) * hys: Manipulating Hyphenation. (line 369) * ie: if-else. (line 7) * if: if-then. (line 7) * ig: Comments. (line 54) * in: Line Layout. (line 86) * it: Input Line Traps. (line 7) * itc: Input Line Traps. (line 8) * kern: Ligatures and Kerning. (line 41) * lc: Leaders. (line 22) * length: Strings. (line 135) * lf: Debugging. (line 31) * lg: Ligatures and Kerning. (line 23) * linetabs: Tabs and Fields. (line 139) * ll: Line Layout. (line 138) * ls: Manipulating Spacing. (line 57) * lsm: Leading Space Traps. (line 7) * lt: Page Layout. (line 53) * mc: Miscellaneous. (line 110) * mk: Page Motions. (line 10) * mso: I/O. (line 49) * msoquiet: I/O. (line 50) * na: Manipulating Filling and Adjustment. (line 150) * ne: Page Control. (line 31) * nf: Manipulating Filling and Adjustment. (line 74) * nh: Manipulating Hyphenation. (line 228) * nm: Miscellaneous. (line 9) * nn: Miscellaneous. (line 74) * nop: if-then. (line 26) * nr: ms Document Control Settings. (line 11) * nr <1>: Setting Registers. (line 10) * nr <2>: Setting Registers. (line 64) * nr <3>: Auto-increment. (line 14) * nroff: troff and nroff Modes. (line 33) * ns: Manipulating Spacing. (line 116) * nx: I/O. (line 90) * open: I/O. (line 207) * opena: I/O. (line 208) * os: Page Control. (line 66) * output: Diversions. (line 195) * pc: Page Layout. (line 68) * pev: Debugging. (line 78) * pi: I/O. (line 149) * pl: Page Layout. (line 9) * pm: Debugging. (line 82) * pn: Page Layout. (line 23) * pnr: Debugging. (line 86) * po: Line Layout. (line 60) * ps: Changing the Type Size. (line 7) * psbb: Miscellaneous. (line 158) * pso: I/O. (line 38) * ptr: Debugging. (line 90) * pvs: Changing the Vertical Spacing. (line 48) * rchar: Using Symbols. (line 410) * rd: I/O. (line 95) * return: Writing Macros. (line 163) * rfschar: Using Symbols. (line 411) * rj: Manipulating Filling and Adjustment. (line 247) * rm: Strings. (line 193) * rn: Strings. (line 190) * rnn: Setting Registers. (line 105) * rr: Setting Registers. (line 99) * rs: Manipulating Spacing. (line 117) * rt: Page Motions. (line 11) * schar: Using Symbols. (line 354) * shc: Manipulating Hyphenation. (line 97) * shift: Parameters. (line 30) * sizes: Changing the Type Size. (line 71) * so: I/O. (line 9) * soquiet: I/O. (line 10) * sp: Manipulating Spacing. (line 10) * special: Special Fonts. (line 17) * spreadwarn: Debugging. (line 135) * ss: Manipulating Filling and Adjustment. (line 267) * stringdown: Strings. (line 170) * stringup: Strings. (line 171) * sty: Font Families. (line 62) * substring: Strings. (line 153) * sv: Page Control. (line 65) * sy: I/O. (line 171) * ta: Tabs and Fields. (line 13) * tag: Postprocessor Access. (line 58) * taga: Postprocessor Access. (line 59) * tc: Tabs and Fields. (line 127) * ti: Line Layout. (line 110) * tkf: Ligatures and Kerning. (line 60) * tl: Page Layout. (line 39) * tm: Debugging. (line 43) * tm1: Debugging. (line 44) * tmc: Debugging. (line 45) * tr: Character Translations. (line 13) * trf: I/O. (line 57) * trin: Character Translations. (line 14) * trnt: Character Translations. (line 79) * troff: troff and nroff Modes. (line 25) * uf: Artificial Fonts. (line 90) * ul: Artificial Fonts. (line 64) * unformat: Diversions. (line 233) * vpt: Vertical Position Traps. (line 13) * vs: Changing the Vertical Spacing. (line 7) * warn: Debugging. (line 154) * warnscale: Debugging. (line 131) * wh: Page Location Traps. (line 11) * while: while. (line 10) * write: I/O. (line 219) * writec: I/O. (line 220) * writem: I/O. (line 231)