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Diff for /mandoc/roff.7 between version 1.45 and 1.115

version 1.45, 2013/12/15 21:23:52 version 1.115, 2020/10/28 21:07:47
Line 1 
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 .\"     $Id$  .\"     $Id$
 .\"  .\"
 .\" Copyright (c) 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>  .\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
 .\" Copyright (c) 2010, 2011 Ingo Schwarze <schwarze@openbsd.org>  .\" Copyright (c) 2010-2019 Ingo Schwarze <schwarze@openbsd.org>
 .\"  .\"
 .\" Permission to use, copy, modify, and distribute this software for any  .\" Permission to use, copy, modify, and distribute this software for any
 .\" purpose with or without fee is hereby granted, provided that the above  .\" purpose with or without fee is hereby granted, provided that the above
Line 32  and
Line 32  and
 manual formatting languages are based on it,  manual formatting languages are based on it,
 many real-world manuals use small numbers of  many real-world manuals use small numbers of
 .Nm  .Nm
 requests intermixed with their  requests and escape sequences intermixed with their
 .Xr mdoc 7  .Xr mdoc 7
 or  or
 .Xr man 7  .Xr man 7
 code.  code.
 To properly format such manuals, the  To properly format such manuals, the
 .Xr mandoc 1  .Xr mandoc 1
 utility supports a tiny subset of  utility supports a subset of
 .Nm  .Nm
 requests.  requests and escapes.
 Only these requests supported by  Even though this manual page lists all
   .Nm
   requests and escape sequences, it only contains partial information
   about requests not supported by
 .Xr mandoc 1  .Xr mandoc 1
 are documented in the present manual,  and about language features that do not matter for manual pages.
 together with the basic language syntax shared by  
 .Nm ,  
 .Xr mdoc 7 ,  
 and  
 .Xr man 7 .  
 For complete  For complete
 .Nm  .Nm
 manuals, consult the  manuals, consult the
Line 85  documents may contain only graphable 7-bit ASCII chara
Line 83  documents may contain only graphable 7-bit ASCII chara
 character, and, in certain circumstances, the tab character.  character, and, in certain circumstances, the tab character.
 The backslash character  The backslash character
 .Sq \e  .Sq \e
 indicates the start of an escape sequence for  indicates the start of an escape sequence, used for example for
 .Sx Comments ,  .Sx Comments
 .Sx Special Characters ,  
 .Sx Predefined Strings ,  
 and  and
 user-defined strings defined using the  .Sx Special Characters .
 .Sx ds  For a complete listing of escape sequences, consult the
 request.  .Sx ESCAPE SEQUENCE REFERENCE
   below.
 .Ss Comments  .Ss Comments
 Text following an escaped double-quote  Text following an escaped double-quote
 .Sq \e\(dq ,  .Sq \e\(dq ,
Line 136  One-letter backslash escape.
Line 133  One-letter backslash escape.
 See  See
 .Xr mandoc_char 7  .Xr mandoc_char 7
 for a complete list.  for a complete list.
 .Ss Text Decoration  .Ss Font Selection
 Terms may be text-decorated using the  In
 .Sq \ef  .Xr mdoc 7
 escape followed by an indicator: B (bold), I (italic), R (regular), or P  and
 (revert to previous mode).  .Xr man 7
 A numerical representation 3, 2, or 1 (bold, italic, and regular,  documents, fonts are usually selected with macros.
 respectively) may be used instead.  The
 The indicator or numerical representative may be preceded by C  .Ic \ef
 (constant-width), which is ignored.  escape sequence and the
   .Ic \&ft
   request can be used to manually change the font,
   but this is not recommended in
   .Xr mdoc 7
   documents.
   Such manual font changes are overridden by many subsequent macros.
 .Pp  .Pp
 The two-character indicator  The following fonts are supported:
 .Sq BI  
 requests a font that is both bold and italic.  
 It may not be portable to old roff implementations.  
 .Pp  .Pp
   .Bl -tag -width CW -offset indent -compact
   .It Cm B
   Bold font.
   .It Cm BI
   A font that is both bold and italic.
   .It Cm CB
   Bold constant width font.
   Same as
   .Cm B
   in terminal output.
   .It Cm CI
   Italic constant width font.
   Same as
   .Cm I
   in terminal output.
   .It Cm CR
   Regular constant width font.
   Same as
   .Cm R
   in terminal output.
   .It Cm CW
   An alias for
   .Cm CR .
   .It Cm I
   Italic font.
   .It Cm P
   Return to the previous font.
   If a macro caused a font change since the last
   .Ic \ef
   eascape sequence or
   .Ic \&ft
   request, this returns to the font before the last font change in
   the macro rather than to the font before the last manual font change.
   .It Cm R
   Roman font.
   This is the default font.
   .It Cm 1
   An alias for
   .Cm R .
   .It Cm 2
   An alias for
   .Cm I .
   .It Cm 3
   An alias for
   .Cm B .
   .It Cm 4
   An alias for
   .Cm BI .
   .El
   .Pp
 Examples:  Examples:
 .Bl -tag -width Ds -offset indent -compact  .Bl -tag -width Ds -offset indent -compact
 .It Li \efBbold\efR  .It Li \efBbold\efR
Line 160  Write in \fIitalic\fP, then return to previous font mo
Line 210  Write in \fIitalic\fP, then return to previous font mo
 .It Li \ef(BIbold italic\efP  .It Li \ef(BIbold italic\efP
 Write in \f(BIbold italic\fP, then return to previous font mode.  Write in \f(BIbold italic\fP, then return to previous font mode.
 .El  .El
 .Pp  
 Text decoration is  
 .Em not  
 recommended for  
 .Xr mdoc 7 ,  
 which encourages semantic annotation.  
 .Ss Predefined Strings  
 Predefined strings, like  
 .Sx Special Characters ,  
 mark special output glyphs.  
 Predefined strings are escaped with the slash-asterisk,  
 .Sq \e* :  
 single-character  
 .Sq \e*X ,  
 two-character  
 .Sq \e*(XX ,  
 and N-character  
 .Sq \e*[N] .  
 .Pp  
 Examples:  
 .Bl -tag -width Ds -offset indent -compact  
 .It Li \e*(Am  
 Two-letter ampersand predefined string.  
 .It Li \e*q  
 One-letter double-quote predefined string.  
 .El  
 .Pp  
 Predefined strings are not recommended for use,  
 as they differ across implementations.  
 Those supported by  
 .Xr mandoc 1  
 are listed in  
 .Xr mandoc_char 7 .  
 Manuals using these predefined strings are almost certainly not portable.  
 .Ss Whitespace  .Ss Whitespace
 Whitespace consists of the space character.  Whitespace consists of the space character.
 In text lines, whitespace is preserved within a line.  In text lines, whitespace is preserved within a line.
Line 203  Unescaped trailing spaces are stripped from text line 
Line 219  Unescaped trailing spaces are stripped from text line 
 literal context.  literal context.
 In general, trailing whitespace on any input line is discouraged for  In general, trailing whitespace on any input line is discouraged for
 reasons of portability.  reasons of portability.
 In the rare case that a blank character is needed at the end of an  In the rare case that a space character is needed at the end of an
 input line, it may be forced by  input line, it may be forced by
 .Sq \e\ \e& .  .Sq \e\ \e& .
 .Pp  .Pp
Line 222  Many requests and macros support scaled widths for the
Line 238  Many requests and macros support scaled widths for the
 The syntax for a scaled width is  The syntax for a scaled width is
 .Sq Li [+-]?[0-9]*.[0-9]*[:unit:] ,  .Sq Li [+-]?[0-9]*.[0-9]*[:unit:] ,
 where a decimal must be preceded or followed by at least one digit.  where a decimal must be preceded or followed by at least one digit.
 Negative numbers, while accepted, are truncated to zero.  
 .Pp  .Pp
 The following scaling units are accepted:  The following scaling units are accepted:
 .Pp  .Pp
Line 232  centimetre
Line 247  centimetre
 .It i  .It i
 inch  inch
 .It P  .It P
 pica (~1/6 inch)  pica (1/6 inch)
 .It p  .It p
 point (~1/72 inch)  point (1/72 inch)
 .It f  .It f
 synonym for  scale
 .Sq u  .Sq u
   by 65536
 .It v  .It v
 default vertical span  default vertical span
 .It m  .It m
Line 251  width of rendered
Line 267  width of rendered
 .Pq en  .Pq en
 character  character
 .It u  .It u
 default horizontal span  default horizontal span for the terminal
 .It M  .It M
 mini-em (~1/100 em)  mini-em (1/100 em)
 .El  .El
 .Pp  .Pp
 Using anything other than  Using anything other than
 .Sq m ,  .Sq m ,
 .Sq n ,  .Sq n ,
 .Sq u ,  
 or  or
 .Sq v  .Sq v
 is necessarily non-portable across output media.  is necessarily non-portable across output media.
Line 300  delimiters
Line 315  delimiters
 The proper spacing is also intelligently preserved if a sentence ends at  The proper spacing is also intelligently preserved if a sentence ends at
 the boundary of a macro line.  the boundary of a macro line.
 .Pp  .Pp
   If an input line happens to end with a period, exclamation or question
   mark that isn't the end of a sentence, append a zero-width space
   .Pq Sq \e& .
   .Pp
 Examples:  Examples:
 .Bd -literal -offset indent -compact  .Bd -literal -offset indent -compact
 Do not end sentences mid-line like this.  Instead,  Do not end sentences mid-line like this.  Instead,
 end a sentence like this.  end a sentence like this.
 A macro would end like this:  A macro would end like this:
 \&.Xr mandoc 1 \&.  \&.Xr mandoc 1 \&.
   An abbreviation at the end of an input line needs escaping, e.g.\e&
   like this.
 .Ed  .Ed
 .Sh REQUEST SYNTAX  .Sh REQUEST SYNTAX
 A request or macro line consists of:  A request or macro line consists of:
Line 338  Macros are provided by the
Line 359  Macros are provided by the
 and  and
 .Xr man 7  .Xr man 7
 languages and can be defined by the  languages and can be defined by the
 .Sx \&de  .Ic \&de
 request.  request.
 When called, they follow the same syntax as requests, except that  When called, they follow the same syntax as requests, except that
 macro arguments may optionally be quoted by enclosing them  macro arguments may optionally be quoted by enclosing them
Line 392  The
Line 413  The
 .Xr mandoc 1  .Xr mandoc 1
 .Nm  .Nm
 parser recognises the following requests.  parser recognises the following requests.
 Note that the  For requests marked as "ignored" or "unsupported", any arguments are
 .Nm  ignored, and the number of arguments is not checked.
 language defines many more requests not implemented in  .Bl -tag -width Ds
 .Xr mandoc 1 .  .It Ic \&ab Op Ar message
 .Ss \&ad  Abort processing.
 Set line adjustment mode.  Currently unsupported.
 This line-scoped request is intended to have one argument to select  .It Ic \&ad Op Cm b | c | l | n | r
 normal, left, right, or centre adjustment for subsequent text.  Set line adjustment mode for subsequent text.
 Currently, it is ignored including its arguments,  Currently ignored.
 and the number of arguments is not checked.  .It Ic \&af Ar registername format
 .Ss \&am  Assign an output format to a number register.
   Currently ignored.
   .It Ic \&aln Ar newname oldname
   Create an alias for a number register.
   Currently unsupported.
   .It Ic \&als Ar newname oldname
   Create an alias for a request, string, macro, or diversion.
   .It Ic \&am Ar macroname Op Ar endmacro
 Append to a macro definition.  Append to a macro definition.
 The syntax of this request is the same as that of  The syntax of this request is the same as that of
 .Sx \&de .  .Ic \&de .
 It is currently ignored by  .It Ic \&am1 Ar macroname Op Ar endmacro
 .Xr mandoc 1 ,  
 as are its children.  
 .Ss \&ami  
 Append to a macro definition, specifying the macro name indirectly.  
 The syntax of this request is the same as that of  
 .Sx \&dei .  
 It is currently ignored by  
 .Xr mandoc 1 ,  
 as are its children.  
 .Ss \&am1  
 Append to a macro definition, switching roff compatibility mode off  Append to a macro definition, switching roff compatibility mode off
 during macro execution.  during macro execution (groff extension).
 The syntax of this request is the same as that of  The syntax of this request is the same as that of
 .Sx \&de1 .  .Ic \&de1 .
 It is currently ignored by  Since
 .Xr mandoc 1 ,  .Xr mandoc 1
 as are its children.  does not implement
 .Ss \&cc  .Nm
 Changes the control character.  compatibility mode at all, it handles this request as an alias for
 Its syntax is as follows:  .Ic \&am .
 .Bd -literal -offset indent  .It Ic \&ami Ar macrostring Op Ar endstring
 .Pf . Cm \&cc Op Ar c  Append to a macro definition, specifying the macro name indirectly
 .Ed  (groff extension).
 .Pp  The syntax of this request is the same as that of
   .Ic \&dei .
   .It Ic \&ami1 Ar macrostring Op Ar endstring
   Append to a macro definition, specifying the macro name indirectly
   and switching roff compatibility mode off during macro execution
   (groff extension).
   The syntax of this request is the same as that of
   .Ic \&dei1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&ami .
   .It Ic \&as Ar stringname Op Ar string
   Append to a user-defined string.
   The syntax of this request is the same as that of
   .Ic \&ds .
   If a user-defined string with the specified name does not yet exist,
   it is set to the empty string before appending.
   .It Ic \&as1 Ar stringname Op Ar string
   Append to a user-defined string, switching roff compatibility mode off
   during macro execution (groff extension).
   The syntax of this request is the same as that of
   .Ic \&ds1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&as .
   .It Ic \&asciify Ar divname
   Fully unformat a diversion.
   Currently unsupported.
   .It Ic \&backtrace
   Print a backtrace of the input stack.
   This is a groff extension and currently ignored.
   .It Ic \&bd Ar font Oo Ar curfont Oc Op Ar offset
   Artificially embolden by repeated printing with small shifts.
   Currently ignored.
   .It Ic \&bleedat Ar left top width height
   Set the BleedBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&blm Ar macroname
   Set a blank line trap.
   Currently unsupported.
   .It Ic \&box Ar divname
   Begin a diversion without including a partially filled line.
   Currently unsupported.
   .It Ic \&boxa Ar divname
   Add to a diversion without including a partially filled line.
   Currently unsupported.
   .It Ic \&bp Oo Cm + Ns | Ns Cm - Oc Ns Ar pagenumber
   Begin a new page.
   Currently ignored.
   .It Ic \&BP Ar source height width position offset flags label
   Define a frame and place a picture in it.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&br
   Break the output line.
   .It Ic \&break
   Break out of the innermost
   .Ic \&while
   loop.
   .It Ic \&breakchar Ar char ...
   Optional line break characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&brnl Ar N
   Break output line after the next
   .Ar N
   input lines.
   This is a Heirloom extension and currently ignored.
   .It Ic \&brp
   Break and spread output line.
   Currently, this is implemented as an alias for
   .Ic \&br .
   .It Ic \&brpnl Ar N
   Break and spread output line after the next
   .Ar N
   input lines.
   This is a Heirloom extension and currently ignored.
   .It Ic \&c2 Op Ar char
   Change the no-break control character.
   Currently unsupported.
   .It Ic \&cc Op Ar char
   Change the control character.
 If  If
 .Ar c  .Ar char
 is not specified, the control character is reset to  is not specified, the control character is reset to
 .Sq \&. .  .Sq \&. .
 Trailing characters are ignored.  Trailing characters are ignored.
 .Ss \&de  .It Ic \&ce Op Ar N
   Center the next
   .Ar N
   input lines without filling.
   .Ar N
   defaults to 1.
   An argument of 0 or less ends centering.
   Currently, high level macros abort centering.
   .It Ic \&cf Ar filename
   Output the contents of a file.
   Ignored because insecure.
   .It Ic \&cflags Ar flags char ...
   Set character flags.
   This is a groff extension and currently ignored.
   .It Ic \&ch Ar macroname Op Ar dist
   Change a trap location.
   Currently ignored.
   .It Ic \&char Ar glyph Op Ar string
   Define or redefine the ASCII character or character escape sequence
   .Ar glyph
   to be rendered as
   .Ar string ,
   which can be empty.
   Only partially supported in
   .Xr mandoc 1 ;
   may interact incorrectly with
   .Ic \&tr .
   .It Ic \&chop Ar stringname
   Remove the last character from a macro, string, or diversion.
   Currently unsupported.
   .It Ic \&class Ar classname char ...
   Define a character class.
   This is a groff extension and currently ignored.
   .It Ic \&close Ar streamname
   Close an open file.
   Ignored because insecure.
   .It Ic \&CL Ar color text
   Print text in color.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&color Op Cm 1 | 0
   Activate or deactivate colors.
   This is a groff extension and currently ignored.
   .It Ic \&composite Ar from to
   Define a name component for composite glyph names.
   This is a groff extension and currently unsupported.
   .It Ic \&continue
   Immediately start the next iteration of a
   .Ic \&while
   loop.
   Currently unsupported.
   .It Ic \&cp Op Cm 1 | 0
   Switch
   .Nm
   compatibility mode on or off.
   Currently ignored.
   .It Ic \&cropat Ar left top width height
   Set the CropBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&cs Ar font Op Ar width Op Ar emsize
   Constant character spacing mode.
   Currently ignored.
   .It Ic \&cu Op Ar N
   Underline next
   .Ar N
   input lines including whitespace.
   Currently ignored.
   .It Ic \&da Ar divname
   Append to a diversion.
   Currently unsupported.
   .It Ic \&dch Ar macroname Op Ar dist
   Change a trap location in the current diversion.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&de Ar macroname Op Ar endmacro
 Define a  Define a
 .Nm  .Nm
 macro.  macro.
 Its syntax can be either  Its syntax can be either
 .Bd -literal -offset indent  .Bd -literal -offset indent
 .Pf . Cm \&de Ar name  .Pf . Ic \&de Ar macroname
 .Ar macro definition  .Ar definition
 \&..  \&..
 .Ed  .Ed
 .Pp  .Pp
 or  or
 .Bd -literal -offset indent  .Bd -literal -offset indent
 .Pf . Cm \&de Ar name Ar end  .Pf . Ic \&de Ar macroname Ar endmacro
 .Ar macro definition  .Ar definition
 .Pf . Ar end  .Pf . Ar endmacro
 .Ed  .Ed
 .Pp  .Pp
 Both forms define or redefine the macro  Both forms define or redefine the macro
 .Ar name  .Ar macroname
 to represent the  to represent the
 .Ar macro definition ,  .Ar definition ,
 which may consist of one or more input lines, including the newline  which may consist of one or more input lines, including the newline
 characters terminating each line, optionally containing calls to  characters terminating each line, optionally containing calls to
 .Nm  .Nm
Line 470  or
Line 645  or
 macros, whichever applies to the document in question.  macros, whichever applies to the document in question.
 .Pp  .Pp
 Specifying a custom  Specifying a custom
 .Ar end  .Ar endmacro
 macro works in the same way as for  works in the same way as for
 .Sx \&ig ;  .Ic \&ig ;
 namely, the call to  namely, the call to
 .Sq Pf . Ar end  .Sq Pf . Ar endmacro
 first ends the  first ends the
 .Ar macro definition ,  .Ar definition ,
 and after that, it is also evaluated as a  and after that, it is also evaluated as a
 .Nm  .Nm
 request or  request or
Line 485  macro, but not as a high-level macro.
Line 660  macro, but not as a high-level macro.
 .Pp  .Pp
 The macro can be invoked later using the syntax  The macro can be invoked later using the syntax
 .Pp  .Pp
 .D1 Pf . Ar name Op Ar argument Op Ar argument ...  .D1 Pf . Ar macroname Op Ar argument Op Ar argument ...
 .Pp  .Pp
 Regarding argument parsing, see  Regarding argument parsing, see
 .Sx MACRO SYNTAX  .Sx MACRO SYNTAX
Line 493  above.
Line 668  above.
 .Pp  .Pp
 The line invoking the macro will be replaced  The line invoking the macro will be replaced
 in the input stream by the  in the input stream by the
 .Ar macro definition ,  .Ar definition ,
 replacing all occurrences of  replacing all occurrences of
 .No \e\e$ Ns Ar N ,  .No \e\e$ Ns Ar N ,
 where  where
Line 513  produces
Line 688  produces
 .D1 \efI\e^XtFree\e^\efP.  .D1 \efI\e^XtFree\e^\efP.
 .Pp  .Pp
 in the input stream, and thus in the output: \fI\^XtFree\^\fP.  in the input stream, and thus in the output: \fI\^XtFree\^\fP.
   Each occurrence of \e\e$* is replaced with all the arguments,
   joined together with single space characters.
   The variant \e\e$@ is similar, except that each argument is
   individually quoted.
 .Pp  .Pp
 Since macros and user-defined strings share a common string table,  Since macros and user-defined strings share a common string table,
 defining a macro  defining a macro
 .Ar name  .Ar macroname
 clobbers the user-defined string  clobbers the user-defined string
 .Ar name ,  .Ar macroname ,
 and the  and the
 .Ar macro definition  .Ar definition
 can also be printed using the  can also be printed using the
 .Sq \e*  .Sq \e*
 string interpolation syntax described below  string interpolation syntax described below
 .Sx ds ,  .Ic ds ,
 but this is rarely useful because every macro definition contains at least  but this is rarely useful because every macro definition contains at least
 one explicit newline character.  one explicit newline character.
 .Pp  .Pp
 In order to prevent endless recursion, both groff and  In order to prevent endless recursion, both groff and
 .Xr mandoc 1  .Xr mandoc 1
 limit the stack depth for expanding macros and strings  limit the stack depth for expanding macros and strings
 to a large, but finite number.  to a large, but finite number, and
 Do not rely on the exact value of this limit.  .Xr mandoc 1
 .Ss \&dei  also limits the length of the expanded input line.
   Do not rely on the exact values of these limits.
   .It Ic \&de1 Ar macroname Op Ar endmacro
 Define a  Define a
 .Nm  .Nm
 macro, specifying the macro name indirectly.  macro that will be executed with
   .Nm
   compatibility mode switched off during macro execution.
   This is a groff extension.
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&de .
   .It Ic \&defcolor Ar newname scheme component ...
   Define a color name.
   This is a groff extension and currently ignored.
   .It Ic \&dei Ar macrostring Op Ar endstring
   Define a
   .Nm
   macro, specifying the macro name indirectly (groff extension).
 The syntax of this request is the same as that of  The syntax of this request is the same as that of
 .Sx \&de .  .Ic \&de .
 It is currently ignored by  The effect is the same as:
 .Xr mandoc 1 ,  .Pp
 as are its children.  .D1 Pf . Cm \&de No \e* Ns Bo Ar macrostring Bc Op \e* Ns Bq Ar endstring
 .Ss \&de1  .It Ic \&dei1 Ar macrostring Op Ar endstring
 Define a  Define a
 .Nm  .Nm
 macro that will be executed with  macro that will be executed with
 .Nm  .Nm
 compatibility mode switched off during macro execution.  compatibility mode switched off during macro execution,
 This is a GNU extension not available in traditional  specifying the macro name indirectly (groff extension).
 .Nm  
 implementations and not even in older versions of groff.  
 Since  Since
 .Xr mandoc 1  .Xr mandoc 1
 does not implement  does not implement
 .Nm  .Nm
 compatibility mode at all, it handles this request as an alias for  compatibility mode at all, it handles this request as an alias for
 .Sx \&de .  .Ic \&dei .
 .Ss \&ds  .It Ic \&device Ar string ...
   .It Ic \&devicem Ar stringname
   These two requests only make sense with the groff-specific intermediate
   output format and are unsupported.
   .It Ic \&di Ar divname
   Begin a diversion.
   Currently unsupported.
   .It Ic \&do Ar command Op Ar argument ...
   Execute
   .Nm
   request or macro line with compatibility mode disabled.
   Currently unsupported.
   .It Ic \&ds Ar stringname Op Oo \(dq Oc Ns Ar string
 Define a user-defined string.  Define a user-defined string.
 Its syntax is as follows:  
 .Pp  
 .D1 Pf . Cm \&ds Ar name Oo \(dq Oc Ns Ar string  
 .Pp  
 The  The
 .Ar name  .Ar stringname
 and  and
 .Ar string  .Ar string
 arguments are space-separated.  arguments are space-separated.
Line 579  including whitespace and double-quote characters, even
Line 782  including whitespace and double-quote characters, even
 The  The
 .Ar string  .Ar string
 can be interpolated into subsequent text by using  can be interpolated into subsequent text by using
 .No \e* Ns Bq Ar name  .No \e* Ns Bq Ar stringname
 for a  for a
 .Ar name  .Ar stringname
 of arbitrary length, or \e*(NN or \e*N if the length of  of arbitrary length, or \e*(NN or \e*N if the length of
 .Ar name  .Ar stringname
 is two or one characters, respectively.  is two or one characters, respectively.
 Interpolation can be prevented by escaping the leading backslash;  Interpolation can be prevented by escaping the leading backslash;
 that is, an asterisk preceded by an even number of backslashes  that is, an asterisk preceded by an even number of backslashes
Line 591  does not trigger string interpolation.
Line 794  does not trigger string interpolation.
 .Pp  .Pp
 Since user-defined strings and macros share a common string table,  Since user-defined strings and macros share a common string table,
 defining a string  defining a string
 .Ar name  .Ar stringname
 clobbers the macro  clobbers the macro
 .Ar name ,  .Ar stringname ,
 and the  and the
 .Ar name  .Ar stringname
 used for defining a string can also be invoked as a macro,  used for defining a string can also be invoked as a macro,
 in which case the following input line will be appended to the  in which case the following input line will be appended to the
 .Ar string ,  .Ar string ,
Line 610  H SYNOPSIS
Line 813  H SYNOPSIS
 .Ed  .Ed
 .Pp  .Pp
 invokes the  invokes the
 .Cm SH  .Ic SH
 macro when used in a  macro when used in a
 .Xr man 7  .Xr man 7
 document.  document.
 Such abuse is of course strongly discouraged.  Such abuse is of course strongly discouraged.
 .Ss \&el  .It Ic \&ds1 Ar stringname Op Oo \(dq Oc Ns Ar string
   Define a user-defined string that will be expanded with
   .Nm
   compatibility mode switched off during string expansion.
   This is a groff extension.
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&ds .
   .It Ic \&dwh Ar dist macroname
   Set a location trap in the current diversion.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&dt Op Ar dist macroname
   Set a trap within a diversion.
   Currently unsupported.
   .It Ic \&ec Op Ar char
   Enable the escape mechanism and change the escape character.
 The  The
 .Qq else  .Ar char
   argument defaults to the backslash
   .Pq Sq \e .
   .It Ic \&ecr
   Restore the escape character.
   Currently unsupported.
   .It Ic \&ecs
   Save the escape character.
   Currently unsupported.
   .It Ic \&el Ar body
   The
   .Dq else
 half of an if/else conditional.  half of an if/else conditional.
 Pops a result off the stack of conditional evaluations pushed by  Pops a result off the stack of conditional evaluations pushed by
 .Sx \&ie  .Ic \&ie
 and uses it as its conditional.  and uses it as its conditional.
 If no stack entries are present (e.g., due to no prior  If no stack entries are present (e.g., due to no prior
 .Sx \&ie  .Ic \&ie
 calls)  calls)
 then false is assumed.  then false is assumed.
 The syntax of this request is similar to  The syntax of this request is similar to
 .Sx \&if  .Ic \&if
 except that the conditional is missing.  except that the conditional is missing.
 .Ss \&EN  .It Ic \&em Ar macroname
   Set a trap at the end of input.
   Currently unsupported.
   .It Ic \&EN
 End an equation block.  End an equation block.
 See  See
 .Sx \&EQ .  .Ic \&EQ .
 .Ss \&EQ  .It Ic \&eo
   Disable the escape mechanism completely.
   .It Ic \&EP
   End a picture started by
   .Ic \&BP .
   This is a Heirloom extension and currently unsupported.
   .It Ic \&EQ
 Begin an equation block.  Begin an equation block.
 See  See
 .Xr eqn 7  .Xr eqn 7
 for a description of the equation language.  for a description of the equation language.
 .Ss \&fam  .It Ic \&errprint Ar message
   Print a string like an error message.
   This is a Heirloom extension and currently ignored.
   .It Ic \&ev Op Ar envname
   Switch to another environment.
   Currently unsupported.
   .It Ic \&evc Op Ar envname
   Copy an environment into the current environment.
   Currently unsupported.
   .It Ic \&ex
   Abort processing and exit.
   Currently unsupported.
   .It Ic \&fallback Ar curfont font ...
   Select the fallback sequence for a font.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fam Op Ar familyname
 Change the font family.  Change the font family.
 This line-scoped request is intended to have one argument specifying  This is a groff extension and currently ignored.
 the font family to be selected.  .It Ic \&fc Op Ar delimchar Op Ar padchar
 It is a groff extension, and currently, it is ignored including its  Define a delimiting and a padding character for fields.
 arguments, and the number of arguments is not checked.  Currently unsupported.
 .Ss \&hw  .It Ic \&fchar Ar glyphname Op Ar string
   Define a fallback glyph.
   Currently unsupported.
   .It Ic \&fcolor Ar colorname
   Set the fill color for \eD objects.
   This is a groff extension and currently ignored.
   .It Ic \&fdeferlig Ar font string ...
   Defer ligature building.
   This is a Heirloom extension and currently ignored.
   .It Ic \&feature Cm + Ns | Ns Cm - Ns Ar name
   Enable or disable an OpenType feature.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fi
   Break the output line and switch to fill mode,
   which is active by default but can be ended with the
   .Ic \&nf
   request.
   In fill mode, input from subsequent input lines is added to
   the same output line until the next word no longer fits,
   at which point the output line is broken.
   This request is implied by the
   .Xr mdoc 7
   .Ic \&Sh
   macro and by the
   .Xr man 7
   .Ic \&SH ,
   .Ic \&SS ,
   and
   .Ic \&EE
   macros.
   .It Ic \&fkern Ar font minkern
   Control the use of kerning tables for a font.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fl
   Flush output.
   Currently ignored.
   .It Ic \&flig Ar font string char ...
   Define ligatures.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fp Ar position font Op Ar filename
   Assign font position.
   Currently ignored.
   .It Ic \&fps Ar mapname ...
   Mount a font with a special character map.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fschar Ar font glyphname Op Ar string
   Define a font-specific fallback glyph.
   This is a groff extension and currently unsupported.
   .It Ic \&fspacewidth Ar font Op Ar afmunits
   Set a font-specific width for the space character.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fspecial Ar curfont Op Ar font ...
   Conditionally define a special font.
   This is a groff extension and currently ignored.
   .It Ic \&ft Op Ar font
   Change the font; see
   .Sx Font Selection .
   The
   .Ar font
   argument defaults to
   .Cm P .
   .It Ic \&ftr Ar newname Op Ar oldname
   Translate font name.
   This is a groff extension and currently ignored.
   .It Ic \&fzoom Ar font Op Ar permille
   Zoom font size.
   Currently ignored.
   .It Ic \&gcolor Op Ar colorname
   Set glyph color.
   This is a groff extension and currently ignored.
   .It Ic \&hc Op Ar char
   Set the hyphenation character.
   Currently ignored.
   .It Ic \&hcode Ar char code ...
   Set hyphenation codes of characters.
   Currently ignored.
   .It Ic \&hidechar Ar font char ...
   Hide characters in a font.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hla Ar language
   Set hyphenation language.
   This is a groff extension and currently ignored.
   .It Ic \&hlm Op Ar number
   Set maximum number of consecutive hyphenated lines.
   Currently ignored.
   .It Ic \&hpf Ar filename
   Load hyphenation pattern file.
   This is a groff extension and currently ignored.
   .It Ic \&hpfa Ar filename
   Load hyphenation pattern file, appending to the current patterns.
   This is a groff extension and currently ignored.
   .It Ic \&hpfcode Ar code code ...
   Define mapping values for character codes in hyphenation patterns.
   This is a groff extension and currently ignored.
   .It Ic \&hw Ar word ...
 Specify hyphenation points in words.  Specify hyphenation points in words.
 This line-scoped request is currently ignored.  Currently ignored.
 .Ss \&hy  .It Ic \&hy Op Ar mode
 Set automatic hyphenation mode.  Set automatic hyphenation mode.
 This line-scoped request is currently ignored.  Currently ignored.
 .Ss \&ie  .It Ic \&hylang Ar language
   Set hyphenation language.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hylen Ar nchar
   Minimum word length for hyphenation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hym Op Ar length
   Set hyphenation margin.
   This is a groff extension and currently ignored.
   .It Ic \&hypp Ar penalty ...
   Define hyphenation penalties.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hys Op Ar length
   Set hyphenation space.
   This is a groff extension and currently ignored.
   .It Ic \&ie Ar condition body
 The  The
 .Qq if  .Dq if
 half of an if/else conditional.  half of an if/else conditional.
 The result of the conditional is pushed into a stack used by subsequent  The result of the conditional is pushed into a stack used by subsequent
 invocations of  invocations of
 .Sx \&el ,  .Ic \&el ,
 which may be separated by any intervening input (or not exist at all).  which may be separated by any intervening input (or not exist at all).
 Its syntax is equivalent to  Its syntax is equivalent to
 .Sx \&if .  .Ic \&if .
 .Ss \&if  .It Ic \&if Ar condition body
 Begins a conditional.  Begin a conditional.
 Right now, the conditional evaluates to true  This request can also be written as follows:
 if and only if it starts with the letter  .Bd -unfilled -offset indent
 .Sy n ,  .Pf . Ic \&if Ar condition No \e{ Ns Ar body
 indicating processing in nroff style as opposed to troff style.  .Ar body ... Ns \e}
   .Ed
   .Bd -unfilled -offset indent
   .Pf . Ic \&if Ar condition No \e{\e
   .Ar body ...
   .Pf . No \e}
   .Ed
   .Pp
   The
   .Ar condition
   is a boolean expression.
   Currently,
   .Xr mandoc 1
   supports the following subset of roff conditionals:
   .Bl -bullet
   .It
   If
   .Sq \&!
   is prefixed to
   .Ar condition ,
   it is logically inverted.
   .It
   If the first character of
   .Ar condition
   is
   .Sq n
   .Pq nroff mode
   or
   .Sq o
   .Pq odd page ,
   it evaluates to true, and the
   .Ar body
   starts with the next character.
   .It
   If the first character of
   .Ar condition
   is
   .Sq e
   .Pq even page ,
   .Sq t
   .Pq troff mode ,
   or
   .Sq v
   .Pq vroff mode ,
   it evaluates to false, and the
   .Ar body
   starts with the next character.
   .It
   If the first character of
   .Ar condition
   is
   .Sq c
   .Pq character available ,
   it evaluates to true if the following character is an ASCII character
   or a valid character escape sequence, or to false otherwise.
   The
   .Ar body
   starts with the character following that next character.
   .It
   If the first character of
   .Ar condition
   is
   .Sq d ,
   it evaluates to true if the rest of
   .Ar condition
   is the name of an existing user defined macro or string;
   otherwise, it evaluates to false.
   .It
   If the first character of
   .Ar condition
   is
   .Sq r ,
   it evaluates to true if the rest of
   .Ar condition
   is the name of an existing number register;
   otherwise, it evaluates to false.
   .It
   If the
   .Ar condition
   starts with a parenthesis or with an optionally signed
   integer number, it is evaluated according to the rules of
   .Sx Numerical expressions
   explained below.
   It evaluates to true if the result is positive,
   or to false if the result is zero or negative.
   .It
   Otherwise, the first character of
   .Ar condition
   is regarded as a delimiter and it evaluates to true if the string
   extending from its first to its second occurrence is equal to the
   string extending from its second to its third occurrence.
   .It
   If
   .Ar condition
   cannot be parsed, it evaluates to false.
   .El
   .Pp
 If a conditional is false, its children are not processed, but are  If a conditional is false, its children are not processed, but are
 syntactically interpreted to preserve the integrity of the input  syntactically interpreted to preserve the integrity of the input
 document.  document.
Line 683  will continue to syntactically interpret to the block 
Line 1144  will continue to syntactically interpret to the block 
 conditional.  conditional.
 Sub-conditionals, in this case, obviously inherit the truth value of  Sub-conditionals, in this case, obviously inherit the truth value of
 the parent.  the parent.
 This request has the following syntax:  
 .Bd -literal -offset indent  
 \&.if COND \e{\e  
 BODY...  
 \&.\e}  
 .Ed  
 .Bd -literal -offset indent  
 \&.if COND \e{ BODY  
 BODY... \e}  
 .Ed  
 .Bd -literal -offset indent  
 \&.if COND \e{ BODY  
 BODY...  
 \&.\e}  
 .Ed  
 .Bd -literal -offset indent  
 \&.if COND \e  
 BODY  
 .Ed  
 .Pp  .Pp
 COND is a conditional statement.  If the
 roff allows for complicated conditionals; mandoc is much simpler.  .Ar body
 At this time, mandoc supports only  section is begun by an escaped brace
 .Sq n ,  
 evaluating to true;  
 and  
 .Sq t ,  
 .Sq e ,  
 and  
 .Sq o ,  
 evaluating to false.  
 All other invocations are read up to the next end of line or space and  
 evaluate as false.  
 .Pp  
 If the BODY section is begun by an escaped brace  
 .Sq \e{ ,  .Sq \e{ ,
 scope continues until a closing-brace escape sequence  scope continues until the end of the input line containing the
 .Sq \.\e} .  matching closing-brace escape sequence
 If the BODY is not enclosed in braces, scope continues until  .Sq \e} .
 the end of the line.  If the
 If the COND is followed by a BODY on the same line, whether after a  .Ar body
 brace or not, then requests and macros  is not enclosed in braces, scope continues until the end of the line.
   If the
   .Ar condition
   is followed by a
   .Ar body
   on the same line, whether after a brace or not, then requests and macros
 .Em must  .Em must
 begin with a control character.  begin with a control character.
 It is generally more intuitive, in this case, to write  It is generally more intuitive, in this case, to write
 .Bd -literal -offset indent  .Bd -unfilled -offset indent
 \&.if COND \e{\e  .Pf . Ic \&if Ar condition No \e{\e
 \&.foo  .Pf . Ar request
 bar  .Pf . No \e}
 \&.\e}  
 .Ed  .Ed
 .Pp  .Pp
 than having the request or macro follow as  than having the request or macro follow as
 .Pp  .Pp
 .D1 \&.if COND \e{ .foo  .D1 Pf . Ic \&if Ar condition Pf \e{. Ar request
 .Pp  .Pp
 The scope of a conditional is always parsed, but only executed if the  The scope of a conditional is always parsed, but only executed if the
 conditional evaluates to true.  conditional evaluates to true.
Line 756  will result in
Line 1190  will result in
 being considered an argument of the  being considered an argument of the
 .Sq \&Fl  .Sq \&Fl
 macro.  macro.
 .Ss \&ig  .It Ic \&ig Op Ar endmacro
 Ignore input.  Ignore input.
 Its syntax can be either  Its syntax can be either
 .Bd -literal -offset indent  .Bd -literal -offset indent
Line 767  Its syntax can be either
Line 1201  Its syntax can be either
 .Pp  .Pp
 or  or
 .Bd -literal -offset indent  .Bd -literal -offset indent
 .Pf . Cm \&ig Ar end  .Pf . Cm \&ig Ar endmacro
 .Ar ignored text  .Ar ignored text
 .Pf . Ar end  .Pf . Ar endmacro
 .Ed  .Ed
 .Pp  .Pp
 In the first case, input is ignored until a  In the first case, input is ignored until a
 .Sq \&..  .Sq \&..
 request is encountered on its own line.  request is encountered on its own line.
 In the second case, input is ignored until the specified  In the second case, input is ignored until the specified
 .Sq Pf . Ar end  .Sq Pf . Ar endmacro
 macro is encountered.  is encountered.
 Do not use the escape character  Do not use the escape character
 .Sq \e  .Sq \e
 anywhere in the definition of  anywhere in the definition of
 .Ar end ;  .Ar endmacro ;
 it would cause very strange behaviour.  it would cause very strange behaviour.
 .Pp  .Pp
 When the  When the
 .Ar end  .Ar endmacro
 macro is a roff request or a roff macro, like in  is a roff request or a roff macro, like in
 .Pp  .Pp
 .D1 \&.ig if  .D1 \&.ig if
 .Pp  .Pp
 the subsequent invocation of  the subsequent invocation of
 .Sx \&if  .Ic \&if
 will first terminate the  will first terminate the
 .Ar ignored text ,  .Ar ignored text ,
 then be invoked as usual.  then be invoked as usual.
Line 800  Otherwise, it only terminates the
Line 1234  Otherwise, it only terminates the
 and arguments following it or the  and arguments following it or the
 .Sq \&..  .Sq \&..
 request are discarded.  request are discarded.
 .Ss \&ne  .It Ic \&in Op Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Change indentation.
   See
   .Xr man 7 .
   Ignored in
   .Xr mdoc 7 .
   .It Ic \&index Ar register stringname substring
   Find a substring in a string.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&it Ar expression macro
   Set an input line trap.
   The named
   .Ar macro
   will be invoked after processing the number of input text lines
   specified by the numerical
   .Ar expression .
   While evaluating the
   .Ar expression ,
   the unit suffixes described below
   .Sx Scaling Widths
   are ignored.
   .It Ic \&itc Ar expression macro
   Set an input line trap, not counting lines ending with \ec.
   Currently unsupported.
   .It Ic \&IX Ar class keystring
   To support the generation of a table of contents,
   .Xr pod2man 1
   emits this user-defined macro, usually without defining it.
   To avoid reporting large numbers of spurious errors,
   .Xr mandoc 1
   ignores it.
   .It Ic \&kern Op Cm 1 | 0
   Switch kerning on or off.
   Currently ignored.
   .It Ic \&kernafter Ar font char ... afmunits ...
   Increase kerning after some characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&kernbefore Ar font char ... afmunits ...
   Increase kerning before some characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&kernpair Ar font char ... font char ... afmunits
   Add a kerning pair to the kerning table.
   This is a Heirloom extension and currently ignored.
   .It Ic \&lc Op Ar glyph
   Define a leader repetition character.
   Currently unsupported.
   .It Ic \&lc_ctype Ar localename
   Set the
   .Dv LC_CTYPE
   locale.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&lds Ar macroname string
   Define a local string.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&length Ar register string
   Count the number of input characters in a string.
   Currently unsupported.
   .It Ic \&letadj Ar lspmin lshmin letss lspmax lshmax
   Dynamic letter spacing and reshaping.
   This is a Heirloom extension and currently ignored.
   .It Ic \&lf Ar lineno Op Ar filename
   Change the line number for error messages.
   Ignored because insecure.
   .It Ic \&lg Op Cm 1 | 0
   Switch the ligature mechanism on or off.
   Currently ignored.
   .It Ic \&lhang Ar font char ... afmunits
   Hang characters at left margin.
   This is a Heirloom extension and currently ignored.
   .It Ic \&linetabs Op Cm 1 | 0
   Enable or disable line-tabs mode.
   This is a groff extension and currently unsupported.
   .It Ic \&ll Op Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Change the output line length.
   If the
   .Ar width
   argument is omitted, the line length is reset to its previous value.
   The default setting for terminal output is 78n.
   If a sign is given, the line length is added to or subtracted from;
   otherwise, it is set to the provided value.
   Using this request in new manuals is discouraged for several reasons,
   among others because it overrides the
   .Xr mandoc 1
   .Fl O Cm width
   command line option.
   .It Ic \&lnr Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar value Op Ar increment
   Set local number register.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&lnrf Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar value Op Ar increment
   Set local floating-point register.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&lpfx Ar string
   Set a line prefix.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&ls Op Ar factor
   Set line spacing.
   It takes one integer argument specifying the vertical distance of
   subsequent output text lines measured in v units.
   Currently ignored.
   .It Ic \&lsm Ar macroname
   Set a leading spaces trap.
   This is a groff extension and currently unsupported.
   .It Ic \&lt Op Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Set title line length.
   Currently ignored.
   .It Ic \&mc Ar glyph Op Ar dist
   Print margin character in the right margin.
   The
   .Ar dist
   is currently ignored; instead, 1n is used.
   .It Ic \&mediasize Ar media
   Set the device media size.
   This is a Heirloom extension and currently ignored.
   .It Ic \&minss Ar width
   Set minimum word space.
   This is a Heirloom extension and currently ignored.
   .It Ic \&mk Op Ar register
   Mark vertical position.
   Currently ignored.
   .It Ic \&mso Ar filename
   Load a macro file using the search path.
   Ignored because insecure.
   .It Ic \&na
   Disable adjusting without changing the adjustment mode.
   Currently ignored.
   .It Ic \&ne Op Ar height
 Declare the need for the specified minimum vertical space  Declare the need for the specified minimum vertical space
 before the next trap or the bottom of the page.  before the next trap or the bottom of the page.
 This line-scoped request is currently ignored.  Currently ignored.
 .Ss \&nh  .It Ic \&nf
   Break the output line and switch to no-fill mode.
   Subsequent input lines are kept together on the same output line
   even when exceeding the right margin,
   and line breaks in subsequent input cause output line breaks.
   This request is implied by the
   .Xr mdoc 7
   .Ic \&Bd Fl unfilled
   and
   .Ic \&Bd Fl literal
   macros and by the
   .Xr man 7
   .Ic \&EX
   macro.
   The
   .Ic \&fi
   request switches back to the default fill mode.
   .It Ic \&nh
 Turn off automatic hyphenation mode.  Turn off automatic hyphenation mode.
 This line-scoped request is currently ignored.  Currently ignored.
 .Ss \&rm  .It Ic \&nhychar Ar char ...
 Remove a request, macro or string.  Define hyphenation-inhibiting characters.
 This request is intended to have one argument,  This is a Heirloom extension and currently ignored.
 the name of the request, macro or string to be undefined.  .It Ic \&nm Op Ar start Op Ar inc Op Ar space Op Ar indent
 Currently, it is ignored including its arguments,  Print line numbers.
 and the number of arguments is not checked.  Currently unsupported.
 .Ss \&nr  .It Ic \&nn Op Ar number
   Temporarily turn off line numbering.
   Currently unsupported.
   .It Ic \&nop Ar body
   Execute the rest of the input line as a request, macro, or text line,
   skipping the
   .Ic \&nop
   request and any space characters immediately following it.
   This is mostly used to indent text lines inside macro definitions.
   .It Ic \&nr Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar expression Op Ar stepsize
 Define or change a register.  Define or change a register.
 A register is an arbitrary string value that defines some sort of state,  A register is an arbitrary string value that defines some sort of state,
 which influences parsing and/or formatting.  which influences parsing and/or formatting.
 Its syntax is as follows:  For the syntax of
   .Ar expression ,
   see
   .Sx Numerical expressions
   below.
   If it is prefixed by a sign, the register will be
   incremented or decremented instead of assigned to.
 .Pp  .Pp
 .D1 Pf \. Cm \&nr Ar name Oo +|- Oc Ns Ar value  
 .Pp  
 The  The
 .Ar value  .Ar stepsize
 may, at the moment, only be an integer.  is used by the
 If it is prefixed by a sign, the register will be  .Ic \en+
 incremented or decremented instead of assigned to.  auto-increment feature.
   It remains unchanged when omitted while changing an existing register,
   and it defaults to 0 when defining a new register.
 .Pp  .Pp
 The following register  The following
 .Ar name  .Ar register
 is handled specially:  is handled specially:
 .Bl -tag -width Ds  .Bl -tag -width Ds
 .It Cm nS  .It Cm nS
Line 845  section itself.
Line 1436  section itself.
 Note that starting a new  Note that starting a new
 .Xr mdoc 7  .Xr mdoc 7
 section with the  section with the
 .Cm \&Sh  .Ic \&Sh
 macro will reset this register.  macro will reset this register.
 .El  .El
 .Ss \&ns  .It Xo
   .Ic \&nrf Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar expression
   .Op Ar increment
   .Xc
   Define or change a floating-point register.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&nroff
   Force nroff mode.
   This is a groff extension and currently ignored.
   .It Ic \&ns
 Turn on no-space mode.  Turn on no-space mode.
 This line-scoped request is intended to take no arguments.  Currently ignored.
 Currently, it is ignored including its arguments,  .It Ic \&nx Op Ar filename
 and the number of arguments is not checked.  Abort processing of the current input file and process another one.
 .Ss \&ps  Ignored because insecure.
   .It Ic \&open Ar stream file
   Open a file for writing.
   Ignored because insecure.
   .It Ic \&opena Ar stream file
   Open a file for appending.
   Ignored because insecure.
   .It Ic \&os
   Output saved vertical space.
   Currently ignored.
   .It Ic \&output Ar string
   Output directly to intermediate output.
   Not supported.
   .It Ic \&padj Op Cm 1 | 0
   Globally control paragraph-at-once adjustment.
   This is a Heirloom extension and currently ignored.
   .It Ic \&papersize Ar media
   Set the paper size.
   This is a Heirloom extension and currently ignored.
   .It Ic \&pc Op Ar char
   Change the page number character.
   Currently ignored.
   .It Ic \&pev
   Print environments.
   This is a groff extension and currently ignored.
   .It Ic \&pi Ar command
   Pipe output to a shell command.
   Ignored because insecure.
   .It Ic \&PI
   Low-level request used by
   .Ic \&BP .
   This is a Heirloom extension and currently unsupported.
   .It Ic \&pl Op Oo Cm + Ns | Ns Cm - Oc Ns Ar height
   Change page length.
   Currently ignored.
   .It Ic \&pm
   Print names and sizes of macros, strings, and diversions
   to standard error output.
   Currently ignored.
   .It Ic \&pn Oo Cm + Ns | Ns Cm - Oc Ns Ar number
   Change the page number of the next page.
   Currently ignored.
   .It Ic \&pnr
   Print all number registers on standard error output.
   Currently ignored.
   .It Ic \&po Op Oo Cm + Ns | Ns Cm - Oc Ns Ar offset
   Set a horizontal page offset.
   If no argument is specified, the page offset is reverted to its
   previous value.
   If a sign is specified, the new page offset is calculated relative
   to the current one; otherwise, it is absolute.
   The argument follows the syntax of
   .Sx Scaling Widths
   and the default scaling unit is
   .Cm m .
   .It Ic \&ps Op Oo Cm + Ns | Ns Cm - Oc Ns size
 Change point size.  Change point size.
 This line-scoped request is intended to take one numerical argument.  Currently ignored.
 Currently, it is ignored including its arguments,  .It Ic \&psbb Ar filename
 and the number of arguments is not checked.  Retrieve the bounding box of a PostScript file.
 .Ss \&so  Currently unsupported.
   .It Ic \&pshape Ar indent length ...
   Set a special shape for the current paragraph.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&pso Ar command
   Include output of a shell command.
   Ignored because insecure.
   .It Ic \&ptr
   Print the names and positions of all traps on standard error output.
   This is a groff extension and currently ignored.
   .It Ic \&pvs Op Oo Cm + Ns | Ns Cm - Oc Ns Ar height
   Change post-vertical spacing.
   This is a groff extension and currently ignored.
   .It Ic \&rchar Ar glyph ...
   Remove glyph definitions.
   Currently unsupported.
   .It Ic \&rd Op Ar prompt Op Ar argument ...
   Read from standard input.
   Currently ignored.
   .It Ic \&recursionlimit Ar maxrec maxtail
   Set the maximum stack depth for recursive macros.
   This is a Heirloom extension and currently ignored.
   .It Ic \&return Op Ar twice
   Exit the presently executed macro and return to the caller.
   The argument is currently ignored.
   .It Ic \&rfschar Ar font glyph ...
   Remove font-specific fallback glyph definitions.
   Currently unsupported.
   .It Ic \&rhang Ar font char ... afmunits
   Hang characters at right margin.
   This is a Heirloom extension and currently ignored.
   .It Ic \&rj Op Ar N
   Justify the next
   .Ar N
   input lines to the right margin without filling.
   .Ar N
   defaults to 1.
   An argument of 0 or less ends right adjustment.
   .It Ic \&rm Ar macroname
   Remove a request, macro or string.
   .It Ic \&rn Ar oldname newname
   Rename a request, macro, diversion, or string.
   In
   .Xr mandoc 1 ,
   user-defined macros,
   .Xr mdoc 7
   and
   .Xr man 7
   macros, and user-defined strings can be renamed, but renaming of
   predefined strings and of
   .Nm
   requests is not supported, and diversions are not implemented at all.
   .It Ic \&rnn Ar oldname newname
   Rename a number register.
   Currently unsupported.
   .It Ic \&rr Ar register
   Remove a register.
   .It Ic \&rs
   End no-space mode.
   Currently ignored.
   .It Ic \&rt Op Ar dist
   Return to marked vertical position.
   Currently ignored.
   .It Ic \&schar Ar glyph Op Ar string
   Define global fallback glyph.
   This is a groff extension and currently unsupported.
   .It Ic \&sentchar Ar char ...
   Define sentence-ending characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&shc Op Ar glyph
   Change the soft hyphen character.
   Currently ignored.
   .It Ic \&shift Op Ar number
   Shift macro arguments
   .Ar number
   times, by default once: \e\e$i becomes what \e\e$i+number was.
   Also decrement \en(.$ by
   .Ar number .
   .It Ic \&sizes Ar size ...
   Define permissible point sizes.
   This is a groff extension and currently ignored.
   .It Ic \&so Ar filename
 Include a source file.  Include a source file.
 Its syntax is as follows:  The file is read and its contents processed as input in place of the
 .Pp  .Ic \&so
 .D1 Pf \. Cm \&so Ar file  
 .Pp  
 The  
 .Ar file  
 will be read and its contents processed as input in place of the  
 .Sq \&.so  
 request line.  request line.
 To avoid inadvertent inclusion of unrelated files,  To avoid inadvertent inclusion of unrelated files,
 .Xr mandoc 1  .Xr mandoc 1
Line 886  Typical usage looks like:
Line 1616  Typical usage looks like:
 .Dl \&.so man3/Xcursor.3  .Dl \&.so man3/Xcursor.3
 .Pp  .Pp
 As the whole concept is rather fragile, the use of  As the whole concept is rather fragile, the use of
 .Sx \&so  .Ic \&so
 is discouraged.  is discouraged.
 Use  Use
 .Xr ln 1  .Xr ln 1
 instead.  instead.
 .Ss \&ta  .It Ic \&sp Op Ar height
   Break the output line and emit vertical space.
   The argument follows the syntax of
   .Sx Scaling Widths
   and defaults to one blank line
   .Pq Li 1v .
   .It Ic \&spacewidth Op Cm 1 | 0
   Set the space width from the font metrics file.
   This is a Heirloom extension and currently ignored.
   .It Ic \&special Op Ar font ...
   Define a special font.
   This is a groff extension and currently ignored.
   .It Ic \&spreadwarn Op Ar width
   Warn about wide spacing between words.
   Currently ignored.
   .It Ic \&ss Ar wordspace Op Ar sentencespace
   Set space character size.
   Currently ignored.
   .It Ic \&sty Ar position style
   Associate style with a font position.
   This is a groff extension and currently ignored.
   .It Ic \&substring Ar stringname startpos Op Ar endpos
   Replace a user-defined string with a substring.
   Currently unsupported.
   .It Ic \&sv Op Ar height
   Save vertical space.
   Currently ignored.
   .It Ic \&sy Ar command
   Execute shell command.
   Ignored because insecure.
   .It Ic \&T&
   Re-start a table layout, retaining the options of the prior table
   invocation.
   See
   .Ic \&TS .
   .It Ic \&ta Op Ar width ... Op Cm T Ar width ...
 Set tab stops.  Set tab stops.
 This line-scoped request can take an arbitrary number of arguments.  Each
 Currently, it is ignored including its arguments.  .Ar width
 .Ss \&tr  argument follows the syntax of
   .Sx Scaling Widths .
   If prefixed by a plus sign, it is relative to the previous tab stop.
   The arguments after the
   .Cm T
   marker are used repeatedly as often as needed; for each reuse,
   they are taken relative to the last previously established tab stop.
   When
   .Ic \&ta
   is called without arguments, all tab stops are cleared.
   .It Ic \&tc Op Ar glyph
   Change tab repetition character.
   Currently unsupported.
   .It Ic \&TE
   End a table context.
   See
   .Ic \&TS .
   .It Ic \&ti Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Break the output line and indent the next output line by
   .Ar width .
   If a sign is specified, the temporary indentation is calculated
   relative to the current indentation; otherwise, it is absolute.
   The argument follows the syntax of
   .Sx Scaling Widths
   and the default scaling unit is
   .Cm m .
   .It Ic \&tkf Ar font minps width1 maxps width2
   Enable track kerning for a font.
   Currently ignored.
   .It Ic \&tl No \& Ap Ar left Ap Ar center Ap Ar right Ap
   Print a title line.
   Currently unsupported.
   .It Ic \&tm Ar string
   Print to standard error output.
   Currently ignored.
   .It Ic \&tm1 Ar string
   Print to standard error output, allowing leading blanks.
   This is a groff extension and currently ignored.
   .It Ic \&tmc Ar string
   Print to standard error output without a trailing newline.
   This is a groff extension and currently ignored.
   .It Ic \&tr Ar glyph glyph ...
 Output character translation.  Output character translation.
 Its syntax is as follows:  The first glyph in each pair is replaced by the second one.
   Character escapes can be used; for example,
 .Pp  .Pp
 .D1 Pf \. Cm \&tr Ar [ab]+  
 .Pp  
 Pairs of  
 .Ar ab  
 characters are replaced  
 .Ar ( a  
 for  
 .Ar b ) .  
 Replacement (or origin) characters may also be character escapes; thus,  
 .Pp  
 .Dl tr \e(xx\e(yy  .Dl tr \e(xx\e(yy
 .Pp  .Pp
 replaces all invocations of \e(xx with \e(yy.  replaces all invocations of \e(xx with \e(yy.
 .Ss \&T&  .It Ic \&track Ar font minps width1 maxps width2
 Re-start a table layout, retaining the options of the prior table  Static letter space tracking.
 invocation.  This is a Heirloom extension and currently ignored.
 See  .It Ic \&transchar Ar char ...
 .Sx \&TS .  Define transparent characters for sentence-ending.
 .Ss \&TE  This is a Heirloom extension and currently ignored.
 End a table context.  .It Ic \&trf Ar filename
 See  Output the contents of a file, disallowing invalid characters.
 .Sx \&TS .  This is a groff extension and ignored because insecure.
 .Ss \&TS  .It Ic \&trimat Ar left top width height
   Set the TrimBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&trin Ar glyph glyph ...
   Output character translation, ignored by
   .Ic \&asciify .
   Currently unsupported.
   .It Ic \&trnt Ar glyph glyph ...
   Output character translation, ignored by \e!.
   Currently unsupported.
   .It Ic \&troff
   Force troff mode.
   This is a groff extension and currently ignored.
   .It Ic \&TS
 Begin a table, which formats input in aligned rows and columns.  Begin a table, which formats input in aligned rows and columns.
 See  See
 .Xr tbl 7  .Xr tbl 7
 for a description of the tbl language.  for a description of the tbl language.
   .It Ic \&uf Ar font
   Globally set the underline font.
   Currently ignored.
   .It Ic \&ul Op Ar N
   Underline next
   .Ar N
   input lines.
   Currently ignored.
   .It Ic \&unformat Ar divname
   Unformat spaces and tabs in a diversion.
   Currently unsupported.
   .It Ic \&unwatch Ar macroname
   Disable notification for string or macro.
   This is a Heirloom extension and currently ignored.
   .It Ic \&unwatchn Ar register
   Disable notification for register.
   This is a Heirloom extension and currently ignored.
   .It Ic \&vpt Op Cm 1 | 0
   Enable or disable vertical position traps.
   This is a groff extension and currently ignored.
   .It Ic \&vs Op Oo Cm + Ns | Ns Cm - Oc Ns Ar height
   Change vertical spacing.
   Currently ignored.
   .It Ic \&warn Ar flags
   Set warning level.
   Currently ignored.
   .It Ic \&warnscale Ar si
   Set the scaling indicator used in warnings.
   This is a groff extension and currently ignored.
   .It Ic \&watch Ar macroname
   Notify on change of string or macro.
   This is a Heirloom extension and currently ignored.
   .It Ic \&watchlength Ar maxlength
   On change, report the contents of macros and strings
   up to the specified length.
   This is a Heirloom extension and currently ignored.
   .It Ic \&watchn Ar register
   Notify on change of register.
   This is a Heirloom extension and currently ignored.
   .It Ic \&wh Ar dist Op Ar macroname
   Set a page location trap.
   Currently unsupported.
   .It Ic \&while Ar condition body
   Repeated execution while a
   .Ar condition
   is true, with syntax similar to
   .Ic \&if .
   Currently implemented with two restrictions: cannot nest,
   and each loop must start and end in the same scope.
   .It Ic \&write Oo \(dq Oc Ns Ar string
   Write to an open file.
   Ignored because insecure.
   .It Ic \&writec Oo \(dq Oc Ns Ar string
   Write to an open file without appending a newline.
   Ignored because insecure.
   .It Ic \&writem Ar macroname
   Write macro or string to an open file.
   Ignored because insecure.
   .It Ic \&xflag Ar level
   Set the extension level.
   This is a Heirloom extension and currently ignored.
   .El
   .Ss Numerical expressions
   The
   .Ic \&nr ,
   .Ic \&if ,
   and
   .Ic \&ie
   requests accept integer numerical expressions as arguments.
   These are always evaluated using the C
   .Vt int
   type; integer overflow works the same way as in the C language.
   Numbers consist of an arbitrary number of digits
   .Sq 0
   to
   .Sq 9
   prefixed by an optional sign
   .Sq +
   or
   .Sq - .
   Each number may be followed by one optional scaling unit described below
   .Sx Scaling Widths .
   The following equations hold:
   .Bd -literal -offset indent
   1i = 6v = 6P = 10m = 10n = 72p = 1000M = 240u = 240
   254c = 100i = 24000u = 24000
   1f = 65536u = 65536
   .Ed
   .Pp
   The following binary operators are implemented.
   Unless otherwise stated, they behave as in the C language:
   .Pp
   .Bl -tag -width 2n -compact
   .It Ic +
   addition
   .It Ic -
   subtraction
   .It Ic *
   multiplication
   .It Ic /
   division
   .It Ic %
   remainder of division
   .It Ic <
   less than
   .It Ic >
   greater than
   .It Ic ==
   equal to
   .It Ic =
   equal to, same effect as
   .Ic ==
   (this differs from C)
   .It Ic <=
   less than or equal to
   .It Ic >=
   greater than or equal to
   .It Ic <>
   not equal to (corresponds to C
   .Ic != ;
   this one is of limited portability, it is supported by Heirloom roff,
   but not by groff)
   .It Ic &
   logical and (corresponds to C
   .Ic && )
   .It Ic \&:
   logical or (corresponds to C
   .Ic || )
   .It Ic <?
   minimum (not available in C)
   .It Ic >?
   maximum (not available in C)
   .El
   .Pp
   There is no concept of precedence; evaluation proceeds from left to right,
   except when subexpressions are enclosed in parentheses.
   Inside parentheses, whitespace is ignored.
   .Sh ESCAPE SEQUENCE REFERENCE
   The
   .Xr mandoc 1
   .Nm
   parser recognises the following escape sequences.
   In
   .Xr mdoc 7
   and
   .Xr man 7
   documents, using escape sequences is discouraged except for those
   described in the
   .Sx LANGUAGE SYNTAX
   section above.
   .Pp
   A backslash followed by any character not listed here
   simply prints that character itself.
   .Bl -tag -width Ds
   .It Ic \e<newline>
   A backslash at the end of an input line can be used to continue the
   logical input line on the next physical input line, joining the text
   on both lines together as if it were on a single input line.
   .It Ic \e<space>
   The escape sequence backslash-space
   .Pq Sq \e\ \&
   is an unpaddable space-sized non-breaking space character; see
   .Sx Whitespace
   and
   .Xr mandoc_char 7 .
   .It Ic \e!
   Embed text up to and including the end of the input line into the
   current diversion or into intermediate output without interpreting
   requests, macros, and escapes.
   Currently unsupported.
   .It Ic \e\(dq
   The rest of the input line is treated as
   .Sx Comments .
   .It Ic \e#
   Line continuation with comment.
   Discard the rest of the physical input line and continue the logical
   input line on the next physical input line, joining the text on
   both lines together as if it were on a single input line.
   This is a groff extension.
   .It Ic \e$ Ns Ar arg
   Macro argument expansion, see
   .Ic \&de .
   .It Ic \e%
   Hyphenation allowed at this point of the word; ignored by
   .Xr mandoc 1 .
   .It Ic \e&
   Non-printing zero-width character,
   often used for various kinds of escaping; see
   .Sx Whitespace ,
   .Xr mandoc_char 7 ,
   and the
   .Dq MACRO SYNTAX
   and
   .Dq Delimiters
   sections in
   .Xr mdoc 7 .
   .It Ic \e\(aq
   Acute accent special character; use
   .Ic \e(aa
   instead.
   .It Ic \e( Ns Ar cc
   .Sx Special Characters
   with two-letter names, see
   .Xr mandoc_char 7 .
   .It Ic \e)
   Zero-width space transparent to end-of-sentence detection;
   ignored by
   .Xr mandoc 1 .
   .It Ic \e*[ Ns Ar name Ns Ic \&]
   Interpolate the string with the
   .Ar name .
   For short names, there are variants
   .Ic \e* Ns Ar c
   and
   .Ic \e*( Ns Ar cc .
   .Pp
   One string is predefined on the
   .Nm
   language level:
   .Ic \e*(.T
   expands to the name of the output device,
   for example ascii, utf8, ps, pdf, html, or markdown.
   .Pp
   Macro sets traditionally predefine additional strings which are not
   portable and differ across implementations.
   Those supported by
   .Xr mandoc 1
   are listed in
   .Xr mandoc_char 7 .
   .Pp
   Strings can be defined, changed, and deleted with the
   .Ic \&ds ,
   .Ic \&as ,
   and
   .Ic \&rm
   requests.
   .It Ic \e,
   Left italic correction (groff extension); ignored by
   .Xr mandoc 1 .
   .It Ic \e-
   Special character
   .Dq mathematical minus sign ;
   see
   .Xr mandoc_char 7
   for details.
   .It Ic \e/
   Right italic correction (groff extension); ignored by
   .Xr mandoc 1 .
   .It Ic \e:
   Breaking the line is allowed at this point of the word
   without inserting a hyphen.
   .It Ic \e?
   Embed the text up to the next
   .Ic \e?
   into the current diversion without interpreting requests, macros,
   and escapes.
   This is a groff extension and currently unsupported.
   .It Ic \e[ Ns Ar name Ns Ic \&]
   .Sx Special Characters
   with names of arbitrary length, see
   .Xr mandoc_char 7 .
   .It Ic \e^
   One-twelfth em half-narrow space character, effectively zero-width in
   .Xr mandoc 1 .
   .It Ic \e_
   Underline special character; use
   .Ic \e(ul
   instead.
   .It Ic \e`
   Grave accent special character; use
   .Ic \e(ga
   instead.
   .It Ic \e{
   Begin conditional input; see
   .Ic \&if .
   .It Ic \e\(ba
   One-sixth em narrow space character, effectively zero-width in
   .Xr mandoc 1 .
   .It Ic \e}
   End conditional input; see
   .Ic \&if .
   .It Ic \e~
   Paddable non-breaking space character.
   .It Ic \e0
   Digit width space character.
   .It Ic \eA\(aq Ns Ar string Ns Ic \(aq
   Anchor definition; ignored by
   .Xr mandoc 1 .
   .It Ic \ea
   Leader character; ignored by
   .Xr mandoc 1 .
   .It Ic \eB\(aq Ns Ar string Ns Ic \(aq
   Interpolate
   .Sq 1
   if
   .Ar string
   conforms to the syntax of
   .Sx Numerical expressions
   explained above or
   .Sq 0
   otherwise.
   .It Ic \eb\(aq Ns Ar string Ns Ic \(aq
   Bracket building function; ignored by
   .Xr mandoc 1 .
   .It Ic \eC\(aq Ns Ar name Ns Ic \(aq
   .Sx Special Characters
   with names of arbitrary length.
   .It Ic \ec
   When encountered at the end of an input text line,
   the next input text line is considered to continue that line,
   even if there are request or macro lines in between.
   No whitespace is inserted.
   .It Ic \eD\(aq Ns Ar string Ns Ic \(aq
   Draw graphics function; ignored by
   .Xr mandoc 1 .
   .It Ic \ed
   Move down by half a line; ignored by
   .Xr mandoc 1 .
   .It Ic \eE
   Escape character intended to not be interpreted in copy mode.
   In
   .Xr mandoc 1 ,
   it currently does the same as
   .Ic \e
   itself.
   .It Ic \ee
   Backslash special character.
   .It Ic \eF[ Ns Ar name Ns Ic \&]
   Switch font family (groff extension); ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .Ic \eF Ns Ar c
   and
   .Ic \eF( Ns Ar cc .
   .It Ic \ef[ Ns Ar name Ns Ic \&]
   Switch to the font
   .Ar name ,
   see
   .Sx Font Selection .
   For short names, there are variants
   .Ic \ef Ns Ar c
   and
   .Ic \ef( Ns Ar cc .
   An empty name
   .Ic \ef[]
   defaults to
   .Ic \efP .
   .It Ic \eg[ Ns Ar name Ns Ic \&]
   Interpolate the format of a number register; ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .Ic \eg Ns Ar c
   and
   .Ic \eg( Ns Ar cc .
   .It Ic \eH\(aq Ns Oo +|- Oc Ns Ar number Ns Ic \(aq
   Set the height of the current font; ignored by
   .Xr mandoc 1 .
   .It Ic \eh\(aq Ns Oo Cm \&| Oc Ns Ar width Ns Ic \(aq
   Horizontal motion.
   If the vertical bar is given, the motion is relative to the current
   indentation.
   Otherwise, it is relative to the current position.
   The default scaling unit is
   .Cm m .
   .It Ic \ek[ Ns Ar name Ns Ic \&]
   Mark horizontal input place in register; ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .Ic \ek Ns Ar c
   and
   .Ic \ek( Ns Ar cc .
   .It Ic \eL\(aq Ns Ar number Ns Oo Ar c Oc Ns Ic \(aq
   Vertical line drawing function; ignored by
   .Xr mandoc 1 .
   .It Ic \el\(aq Ns Ar width Ns Oo Ar c Oc Ns Ic \(aq
   Draw a horizontal line of
   .Ar width
   using the glyph
   .Ar c .
   .It Ic \eM[ Ns Ar name Ns Ic \&]
   Set fill (background) color (groff extension); ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .Ic \eM Ns Ar c
   and
   .Ic \eM( Ns Ar cc .
   .It Ic \em[ Ns Ar name Ns Ic \&]
   Set glyph drawing color (groff extension); ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .Ic \em Ns Ar c
   and
   .Ic \em( Ns Ar cc .
   .It Ic \eN\(aq Ns Ar number Ns Ic \(aq
   Character
   .Ar number
   on the current font.
   .It Ic \en Ns Oo +|- Oc Ns Ic \&[ Ns Ar name Ns Ic \&]
   Interpolate the number register
   .Ar name .
   For short names, there are variants
   .Ic \en Ns Ar c
   and
   .Ic \en( Ns Ar cc .
   If the optional sign is specified,
   the register is first incremented or decremented by the
   .Ar stepsize
   that was specified in the relevant
   .Ic \&nr
   request, and the changed value is interpolated.
   .It Ic \eO Ns Ar digit , Ic \eO[5 Ns arguments Ns Ic \&]
   Suppress output.
   This is a groff extension and currently unsupported.
   With an argument of
   .Ic 1 , 2 , 3 ,
   or
   .Ic 4 ,
   it is ignored.
   .It Ic \eo\(aq Ns Ar string Ns Ic \(aq
   Overstrike, writing all the characters contained in the
   .Ar string
   to the same output position.
   In terminal and HTML output modes,
   only the last one of the characters is visible.
   .It Ic \ep
   Break the output line at the end of the current word.
   .It Ic \eR\(aq Ns Ar name Oo +|- Oc Ns Ar number Ns Ic \(aq
   Set number register; ignored by
   .Xr mandoc 1 .
   .It Ic \er
   Move up by one line; ignored by
   .Xr mandoc 1 .
   .It Ic \eS\(aq Ns Ar number Ns Ic \(aq
   Slant output; ignored by
   .Xr mandoc 1 .
   .It Ic \es\(aq Ns Oo +|- Oc Ns Ar number Ns Ic \(aq
   Change point size; ignored by
   .Xr mandoc 1 .
   Alternative forms
   .Ic \es Ns Oo +|- Oc Ns Ar n ,
   .Ic \es Ns Oo +|- Oc Ns Ic \(aq Ns Ar number Ns Ic \(aq ,
   .Ic \es[ Ns Oo +|- Oc Ns Ar number Ns Ic \&] ,
   and
   .Ic \es Ns Oo +|- Oc Ns Ic \&[ Ns Ar number Ns Ic \&]
   are also parsed and ignored.
   .It Ic \et
   Horizontal tab; ignored by
   .Xr mandoc 1 .
   .It Ic \eu
   Move up by half a line; ignored by
   .Xr mandoc 1 .
   .It Ic \eV[ Ns Ar name Ns Ic \&]
   Interpolate an environment variable; ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .Ic \eV Ns Ar c
   and
   .Ic \eV( Ns Ar cc .
   .It Ic \ev\(aq Ns Ar number Ns Ic \(aq
   Vertical motion; ignored by
   .Xr mandoc 1 .
   .It Ic \ew\(aq Ns Ar string Ns Ic \(aq
   Interpolate the width of the
   .Ar string .
   The
   .Xr mandoc 1
   implementation assumes that after expansion of user-defined strings, the
   .Ar string
   only contains normal characters, no escape sequences, and that each
   character has a width of 24 basic units.
   .It Ic \eX\(aq Ns Ar string Ns Ic \(aq
   Output
   .Ar string
   as device control function; ignored in nroff mode and by
   .Xr mandoc 1 .
   .It Ic \ex\(aq Ns Ar number Ns Ic \(aq
   Extra line space function; ignored by
   .Xr mandoc 1 .
   .It Ic \eY[ Ns Ar name Ns Ic \&]
   Output a string as a device control function; ignored in nroff mode and by
   .Xr mandoc 1 .
   For short names, there are variants
   .Ic \eY Ns Ar c
   and
   .Ic \eY( Ns Ar cc .
   .It Ic \eZ\(aq Ns Ar string Ns Ic \(aq
   Print
   .Ar string
   with zero width and height; ignored by
   .Xr mandoc 1 .
   .It Ic \ez
   Output the next character without advancing the cursor position.
   .El
 .Sh COMPATIBILITY  .Sh COMPATIBILITY
 This section documents compatibility between mandoc and other  The
   .Xr mandoc 1
   implementation of the
 .Nm  .Nm
 implementations, at this time limited to GNU troff  language is incomplete.
 .Pq Qq groff .  Major unimplemented features include:
 The term  
 .Qq historic groff  
 refers to groff version 1.15.  
 .Pp  .Pp
 .Bl -dash -compact  .Bl -dash -compact
 .It  .It
 In mandoc, the  For security reasons,
 .Sx \&EQ ,  .Xr mandoc 1
 .Sx \&TE ,  never reads or writes external files except via
 .Sx \&TS ,  .Ic \&so
 and  requests with safe relative paths.
 .Sx \&T& ,  
 macros are considered regular macros.  
 In all other  
 .Nm  
 implementations, these are special macros that must be specified without  
 spacing between the control character (which must be a period) and the  
 macro name.  
 .It  .It
   There is no automatic hyphenation, no adjustment to the right margin,
   and very limited support for centering; the output is always set flush-left.
   .It
   Support for setting tabulator and leader characters is missing,
   and support for manually changing indentation is limited.
   .It
 The  The
 .Cm nS  .Sq u
 register is only compatible with OpenBSD's groff-1.15.  scaling unit is the default terminal unit.
   In traditional troff systems, this unit changes depending on the
   output media.
 .It  .It
 Historic groff did not accept white-space before a custom  Width measurements are implemented in a crude way
 .Ar end  and often yield wrong results.
 macro for the  Support for explicit movement requests and escapes is limited.
 .Sx \&ig  
 request.  
 .It  .It
   There is no concept of output pages, no support for floats,
   graphics drawing, and picture inclusion;
   terminal output is always continuous.
   .It
   Requests regarding color, font families, font sizes,
   and glyph manipulation are ignored.
   Font support is very limited.
   Kerning is not implemented, and no ligatures are produced.
   .It
 The  The
 .Sx \&if  .Qq \(aq
 and family would print funny white-spaces with historic groff when  macro control character does not suppress output line breaks.
 using the next-line syntax.  .It
   Diversions and environments are not implemented,
   and support for traps is very incomplete.
   .It
   Use of macros is not supported inside
   .Xr tbl 7
   code.
 .El  .El
   .Pp
   The special semantics of the
   .Cm nS
   number register is an idiosyncrasy of
   .Ox
   manuals and not supported by other
   .Xr mdoc 7
   implementations.
 .Sh SEE ALSO  .Sh SEE ALSO
 .Xr mandoc 1 ,  .Xr mandoc 1 ,
 .Xr eqn 7 ,  .Xr eqn 7 ,
Line 1007  for
Line 2331  for
 .At v2 ,  .At v2 ,
 then ported nroff to C as troff, which Brian W. Kernighan released with  then ported nroff to C as troff, which Brian W. Kernighan released with
 .At v7 .  .At v7 .
 In 1989, James Clarke re-implemented troff in C++, naming it groff.  In 1989, James Clark re-implemented troff in C++, naming it groff.
 .Sh AUTHORS  .Sh AUTHORS
 .An -nosplit  .An -nosplit
 This  This
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