368 lines
9.3 KiB
Groff
368 lines
9.3 KiB
Groff
.\" $Id: mandoc_escape.3,v 1.4 2017/07/04 23:40:01 schwarze Exp $
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.\"
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.\" Copyright (c) 2014 Ingo Schwarze <schwarze@openbsd.org>
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.Dd $Mdocdate: July 4 2017 $
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.Dt MANDOC_ESCAPE 3
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.Os
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.Sh NAME
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.Nm mandoc_escape
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.Nd parse roff escape sequences
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.Sh SYNOPSIS
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.In sys/types.h
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.In mandoc.h
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.Ft "enum mandoc_esc"
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.Fo mandoc_escape
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.Fa "const char **end"
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.Fa "const char **start"
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.Fa "int *sz"
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.Fc
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.Sh DESCRIPTION
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This function scans a
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.Xr roff 7
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escape sequence.
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.Pp
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An escape sequence consists of
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.Bl -dash -compact -width 2n
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.It
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an initial backslash character
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.Pq Sq \e ,
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.It
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a single ASCII character called the escape sequence identifier,
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.It
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and, with only a few exceptions, an argument.
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.El
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.Pp
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Arguments can be given in the following forms; some escape sequence
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identifiers only accept some of these forms as specified below.
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The first three forms are called the standard forms.
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.Bl -tag -width 2n
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.It \&In brackets: Ic \&[ Ns Ar argument Ns Ic \&]
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The argument starts after the initial
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.Sq \&[ ,
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ends before the final
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.Sq \&] ,
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and the escape sequence ends with the final
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.Sq \&] .
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.It Two-character argument short form: Ic \&( Ns Ar ar
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This form can only be used for arguments
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consisting of exactly two characters.
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It has the same effect as
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.Ic \&[ Ns Ar ar Ns Ic \&] .
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.It One-character argument short form: Ar a
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This form can only be used for arguments
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consisting of exactly one character.
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It has the same effect as
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.Ic \&[ Ns Ar a Ns Ic \&] .
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.It Delimited form: Ar C Ns Ar argument Ns Ar C
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The argument starts after the initial delimiter character
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.Ar C ,
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ends before the next occurrence of the delimiter character
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.Ar C ,
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and the escape sequence ends with that second
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.Ar C .
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Some escape sequences allow arbitrary characters
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.Ar C
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as quoting characters, some restrict the range of characters
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that can be used as quoting characters.
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.El
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.Pp
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Upon function entry,
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.Fa end
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is expected to point to the escape sequence identifier.
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The values passed in as
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.Fa start
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and
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.Fa sz
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are ignored and overwritten.
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.Pp
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By design, this function cannot handle those
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.Xr roff 7
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escape sequences that require in-place expansion, in particular
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user-defined strings
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.Ic \e* ,
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number registers
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.Ic \en ,
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width measurements
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.Ic \ew ,
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and numerical expression control
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.Ic \eB .
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These are handled by
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.Fn roff_res ,
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a private preprocessor function called from
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.Fn roff_parseln ,
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see the file
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.Pa roff.c .
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.Pp
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The function
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.Fn mandoc_escape
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is used
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.Bl -dash -compact -width 2n
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.It
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recursively by itself, because some escape sequence arguments can
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in turn contain other escape sequences,
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.It
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for error detection internally by the
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.Xr roff 7
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parser part of the
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.Xr mandoc 3
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library, see the file
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.Pa roff.c ,
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.It
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above all externally by the
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.Xr mandoc 1
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formatting modules, in particular
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.Fl Tascii
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and
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.Fl Thtml ,
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for formatting purposes, see the files
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.Pa term.c
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and
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.Pa html.c ,
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.It
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and rarely externally by high-level utilities using the mandoc library,
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for example
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.Xr makewhatis 8 ,
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to purge escape sequences from text.
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.El
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.Sh RETURN VALUES
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Upon function return, the pointer
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.Fa end
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is set to the character after the end of the escape sequence,
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such that the calling higher-level parser can easily continue.
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.Pp
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For escape sequences taking an argument, the pointer
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.Fa start
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is set to the beginning of the argument and
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.Fa sz
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is set to the length of the argument.
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For escape sequences not taking an argument,
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.Fa start
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is set to the character after the end of the sequence and
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.Fa sz
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is set to 0.
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Both
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.Fa start
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and
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.Fa sz
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may be
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.Dv NULL ;
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in that case, the argument and the length are not returned.
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.Pp
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For sequences taking an argument, the function
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.Fn mandoc_escape
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returns one of the following values:
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.Bl -tag -width 2n
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.It Dv ESCAPE_FONT
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The escape sequence
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.Ic \ef
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taking an argument in standard form:
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.Ic \ef[ , \ef( , \ef Ns Ar a .
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Two-character arguments starting with the character
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.Sq C
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are reduced to one-character arguments by skipping the
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.Sq C .
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More specific values are returned for the most commonly used arguments:
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.Bl -column "argument" "ESCAPE_FONTITALIC"
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.It argument Ta return value
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.It Cm R No or Cm 1 Ta Dv ESCAPE_FONTROMAN
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.It Cm I No or Cm 2 Ta Dv ESCAPE_FONTITALIC
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.It Cm B No or Cm 3 Ta Dv ESCAPE_FONTBOLD
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.It Cm P Ta Dv ESCAPE_FONTPREV
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.It Cm BI Ta Dv ESCAPE_FONTBI
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.El
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.It Dv ESCAPE_SPECIAL
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The escape sequence
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.Ic \eC
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taking an argument delimited with the single quote character
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and, as a special exception, the escape sequences
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.Em not
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having an identifier, that is, those where the argument, in standard
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form, directly follows the initial backslash:
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.Ic \eC' , \e[ , \e( , \e Ns Ar a .
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Note that the one-character argument short form can only be used for
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argument characters that do not clash with escape sequence identifiers.
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.Pp
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If the argument matches one of the forms described below under
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.Dv ESCAPE_UNICODE ,
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that value is returned instead.
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.Pp
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The
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.Dv ESCAPE_SPECIAL
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special character escape sequences can be rendered using the functions
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.Fn mchars_spec2cp
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and
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.Fn mchars_spec2str
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described in the
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.Xr mchars_alloc 3
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manual.
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.It Dv ESCAPE_UNICODE
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Escape sequences of the same format as described above under
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.Dv ESCAPE_SPECIAL ,
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but with an argument of the forms
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.Ic u Ns Ar XXXX ,
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.Ic u Ns Ar YXXXX ,
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or
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.Ic u10 Ns Ar XXXX
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where
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.Ar X
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and
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.Ar Y
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are hexadecimal digits and
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.Ar Y
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is not zero:
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.Ic \eC'u , \e[u .
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As a special exception,
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.Fa start
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is set to the character after the
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.Ic u ,
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and the
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.Fa sz
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return value does not include the
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.Ic u
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either.
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.Pp
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Such Unicode character escape sequences can be rendered using the function
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.Fn mchars_num2uc
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described in the
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.Xr mchars_alloc 3
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manual.
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.It Dv ESCAPE_NUMBERED
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The escape sequence
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.Ic \eN
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followed by a delimited argument.
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The delimiter character is arbitrary except that digits cannot be used.
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If a digit is encountered instead of the opening delimiter, that
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digit is considered to be the argument and the end of the sequence, and
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.Dv ESCAPE_IGNORE
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is returned.
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.Pp
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Such ASCII character escape sequences can be rendered using the function
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.Fn mchars_num2char
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described in the
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.Xr mchars_alloc 3
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manual.
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.It Dv ESCAPE_OVERSTRIKE
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The escape sequence
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.Ic \eo
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followed by an argument delimited by an arbitrary character.
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.It Dv ESCAPE_IGNORE
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.Bl -bullet -width 2n
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.It
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The escape sequence
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.Ic \es
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followed by an argument in standard form or by an argument delimited
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by the single quote character:
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.Ic \es' , \es[ , \es( , \es Ns Ar a .
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As a special exception, an optional
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.Sq +
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or
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.Sq \-
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character is allowed after the
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.Sq s
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for all forms.
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.It
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The escape sequences
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.Ic \eF ,
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.Ic \eg ,
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.Ic \ek ,
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.Ic \eM ,
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.Ic \em ,
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.Ic \en ,
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.Ic \eV ,
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and
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.Ic \eY
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followed by an argument in standard form.
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.It
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The escape sequences
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.Ic \eA ,
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.Ic \eb ,
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.Ic \eD ,
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.Ic \eR ,
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.Ic \eX ,
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and
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.Ic \eZ
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followed by an argument delimited by an arbitrary character.
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.It
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The escape sequences
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.Ic \eH ,
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.Ic \eh ,
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.Ic \eL ,
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.Ic \el ,
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.Ic \eS ,
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.Ic \ev ,
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and
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.Ic \ex
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followed by an argument delimited by a character that cannot occur
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in numerical expressions.
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However, if any character that can occur in numerical expressions
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is found instead of a delimiter, the sequence is considered to end
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with that character, and
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.Dv ESCAPE_ERROR
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is returned.
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.El
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.It Dv ESCAPE_ERROR
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Escape sequences taking an argument but not matching any of the above patterns.
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In particular, that happens if the end of the logical input line
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is reached before the end of the argument.
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.El
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.Pp
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For sequences that do not take an argument, the function
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.Fn mandoc_escape
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returns one of the following values:
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.Bl -tag -width 2n
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.It Dv ESCAPE_SKIPCHAR
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The escape sequence
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.Qq \ez .
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.It Dv ESCAPE_NOSPACE
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The escape sequence
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.Qq \ec .
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.It Dv ESCAPE_IGNORE
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The escape sequences
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.Qq \ed
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and
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.Qq \eu .
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.El
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.Sh FILES
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This function is implemented in
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.Pa mandoc.c .
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.Sh SEE ALSO
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.Xr mchars_alloc 3 ,
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.Xr mandoc_char 7 ,
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.Xr roff 7
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.Sh HISTORY
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This function has been available since mandoc 1.11.2.
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.Sh AUTHORS
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.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
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.An Ingo Schwarze Aq Mt schwarze@openbsd.org
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.Sh BUGS
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The function doesn't cleanly distinguish between sequences that are
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valid and supported, valid and ignored, valid and unsupported,
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syntactically invalid, or undefined.
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For sequences that are ignored or unsupported, it doesn't tell
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whether that deficiency is likely to cause major formatting problems
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and/or loss of document content.
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The function is already rather complicated and still parses some
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sequences incorrectly.
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.
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.ig
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For these sequences, the list given below specifies a starting string
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and either the length of the argument or an ending character.
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The argument starts after the starting string.
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In the former case, the sequence ends with the end of the argument.
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In the latter case, the argument ends before the ending character,
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and the sequence ends with the ending character.
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..
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