path: root/usr.bin/mandoc/mandoc.1

.\" $OpenBSD: mandoc.1,v 1.188 2022/06/28 04:36:29 jsg Exp $
.\"
.\" Copyright (c) 2012, 2014-2022 Ingo Schwarze <schwarze@openbsd.org>
.\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: June 28 2022 $
.Dt MANDOC 1
.Os
.Sh NAME
.Nm mandoc
.Nd format manual pages
.Sh SYNOPSIS
.Nm mandoc
.Op Fl ac
.Op Fl I Cm os Ns = Ns Ar name
.Op Fl K Ar encoding
.Op Fl mdoc | man
.Op Fl O Ar options
.Op Fl T Ar output
.Op Fl W Ar level
.Op Ar
.Sh DESCRIPTION
The
.Nm
utility formats manual pages for display.
.Pp
By default,
.Nm
reads
.Xr mdoc 7
or
.Xr man 7
text from stdin and produces
.Fl T Cm locale
output.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl a
If the standard output is a terminal device and
.Fl c
is not specified, use
.Xr less 1
to paginate the output, just like
.Xr man 1
would.
.It Fl c
Copy the formatted manual pages to the standard output without using
.Xr less 1
to paginate them.
This is the default.
It can be specified to override
.Fl a .
.It Fl I Cm os Ns = Ns Ar name
Override the default operating system
.Ar name
for the
.Xr mdoc 7
.Ic \&Os
and for the
.Xr man 7
.Ic \&TH
macro.
.It Fl K Ar encoding
Specify the input encoding.
The supported
.Ar encoding
arguments are
.Cm us-ascii ,
.Cm iso-8859-1 ,
and
.Cm utf-8 .
If not specified, autodetection uses the first match in the following
list:
.Bl -enum
.It
If the first three bytes of the input file are the UTF-8 byte order
mark (BOM, 0xefbbbf), input is interpreted as
.Cm utf-8 .
.It
If the first or second line of the input file matches the
.Sy emacs
mode line format
.Pp
.D1 .\e" -*- Oo ...; Oc coding: Ar encoding ; No -*-
.Pp
then input is interpreted according to
.Ar encoding .
.It
If the first non-ASCII byte in the file introduces a valid UTF-8
sequence, input is interpreted as
.Cm utf-8 .
.It
Otherwise, input is interpreted as
.Cm iso-8859-1 .
.El
.It Fl mdoc | man
With
.Fl mdoc ,
all input files are interpreted as
.Xr mdoc 7 .
With
.Fl man ,
all input files are interpreted as
.Xr man 7 .
By default, the input language is automatically detected for each file:
if the first macro is
.Ic \&Dd
or
.Ic \&Dt ,
the
.Xr mdoc 7
parser is used; otherwise, the
.Xr man 7
parser is used.
With other arguments,
.Fl m
is silently ignored.
.It Fl O Ar options
Comma-separated output options.
See the descriptions of the individual output formats for supported
.Ar options .
.It Fl T Ar output
Select the output format.
Supported values for the
.Ar output
argument are
.Cm ascii ,
.Cm html ,
the default of
.Cm locale ,
.Cm man ,
.Cm markdown ,
.Cm pdf ,
.Cm ps ,
.Cm tree ,
and
.Cm utf8 .
.Pp
The special
.Fl T Cm lint
mode only parses the input and produces no output.
It implies
.Fl W Cm all
and redirects parser messages, which usually appear on standard
error output, to standard output.
.It Fl W Ar level
Specify the minimum message
.Ar level
to be reported on the standard error output and to affect the exit status.
The
.Ar level
can be
.Cm base ,
.Cm style ,
.Cm warning ,
.Cm error ,
or
.Cm unsupp .
The
.Cm base
level automatically derives the operating system from the contents of the
.Ic \&Os
macro, from the
.Fl Ios
command line option, or from the
.Xr uname 3
return value.
The levels
.Cm openbsd
and
.Cm netbsd
are variants of
.Cm base
that bypass autodetection and request validation of base system
conventions for a particular operating system.
The level
.Cm all
is an alias for
.Cm base .
By default,
.Nm
is silent.
See
.Sx EXIT STATUS
and
.Sx DIAGNOSTICS
for details.
.Pp
The special option
.Fl W Cm stop
tells
.Nm
to exit after parsing a file that causes warnings or errors of at least
the requested level.
No formatted output will be produced from that file.
If both a
.Ar level
and
.Cm stop
are requested, they can be joined with a comma, for example
.Fl W Cm error , Ns Cm stop .
.It Ar file
Read from the given input file.
If multiple files are specified, they are processed in the given order.
If unspecified,
.Nm
reads from standard input.
.El
.Pp
The options
.Fl fhklw
are also supported and are documented in
.Xr man 1 .
In
.Fl f
and
.Fl k
mode,
.Nm
also supports the options
.Fl CMmOSs
described in the
.Xr apropos 1
manual.
The options
.Fl fkl
are mutually exclusive and override each other.
.Ss ASCII Output
Use
.Fl T Cm ascii
to force text output in 7-bit ASCII character encoding documented in the
.Xr ascii 7
manual page, ignoring the
.Xr locale 1
set in the environment.
.Pp
Font styles are applied by using back-spaced encoding such that an
underlined character
.Sq c
is rendered as
.Sq _ Ns \e[bs] Ns c ,
where
.Sq \e[bs]
is the back-space character number 8.
Emboldened characters are rendered as
.Sq c Ns \e[bs] Ns c .
This markup is typically converted to appropriate terminal sequences by
the pager or
.Xr ul 1 .
To remove the markup, pipe the output to
.Xr col 1
.Fl b
instead.
.Pp
The special characters documented in
.Xr mandoc_char 7
are rendered best-effort in an ASCII equivalent.
In particular, opening and closing
.Sq single quotes
are represented as characters number 0x60 and 0x27, respectively,
which agrees with all ASCII standards from 1965 to the latest
revision (2012) and which matches the traditional way in which
.Xr roff 7
formatters represent single quotes in ASCII output.
This correct ASCII rendering may look strange with modern
Unicode-compatible fonts because contrary to ASCII, Unicode uses
the code point U+0060 for the grave accent only, never for an opening
quote.
.Pp
The following
.Fl O
arguments are accepted:
.Bl -tag -width Ds
.It Cm indent Ns = Ns Ar indent
The left margin for normal text is set to
.Ar indent
blank characters instead of the default of five for
.Xr mdoc 7
and seven for
.Xr man 7 .
Increasing this is not recommended; it may result in degraded formatting,
for example overfull lines or ugly line breaks.
When output is to a pager on a terminal that is less than 66 columns
wide, the default is reduced to three columns.
.It Cm mdoc
Format
.Xr man 7
input files in
.Xr mdoc 7
output style.
This prints the operating system name rather than the page title
on the right side of the footer line, and it implies
.Fl O Cm indent Ns =5 .
One useful application is for checking that
.Fl T Cm man
output formats in the same way as the
.Xr mdoc 7
source it was generated from.
.It Cm tag Ns Op = Ns Ar term
If the formatted manual page is opened in a pager,
go to the definition of the
.Ar term
rather than showing the manual page from the beginning.
If no
.Ar term
is specified, reuse the first command line argument that is not a
.Ar section
number.
If that argument is in
.Xr apropos 1
.Ar key Ns = Ns Ar val
format, only the
.Ar val
is used rather than the argument as a whole.
This is useful for commands like
.Ql man -akO tag Ic=ulimit
to search for a keyword and jump right to its definition
in the matching manual pages.
.It Cm width Ns = Ns Ar width
The output width is set to
.Ar width
instead of the default of 78.
When output is to a pager on a terminal that is less than 79 columns
wide, the default is reduced to one less than the terminal width.
In any case, lines that are output in literal mode are never wrapped
and may exceed the output width.
.El
.Ss HTML Output
Output produced by
.Fl T Cm html
conforms to HTML5 using optional self-closing tags.
Equations rendered from
.Xr eqn 7
blocks use MathML.
.Pp
The file
.Pa /usr/share/misc/mandoc.css
documents style-sheet classes available for customising output.
If a style-sheet is not specified with
.Fl O Cm style ,
.Fl T Cm html
defaults to simple output (via an embedded style-sheet)
readable in any graphical or text-based web
browser.
.Pp
Non-ASCII characters are rendered
as hexadecimal Unicode character references.
.Pp
The following
.Fl O
arguments are accepted:
.Bl -tag -width Ds
.It Cm fragment
Omit the <!DOCTYPE> declaration and the <html>, <head>, and <body>
elements and only emit the subtree below the <body> element.
The
.Cm style
argument will be ignored.
This is useful when embedding manual content within existing documents.
.It Cm includes Ns = Ns Ar fmt
The string
.Ar fmt ,
for example,
.Ar ../src/%I.html ,
is used as a template for linked header files (usually via the
.Ic \&In
macro).
Instances of
.Sq \&%I
are replaced with the include filename.
The default is not to present a
hyperlink.
.It Cm man Ns = Ns Ar fmt Ns Op ; Ns Ar fmt
The string
.Ar fmt ,
for example,
.Ar ../html%S/%N.%S.html ,
is used as a template for linked manuals (usually via the
.Ic \&Xr
macro).
Instances of
.Sq \&%N
and
.Sq %S
are replaced with the linked manual's name and section, respectively.
If no section is included, section 1 is assumed.
The default is not to
present a hyperlink.
If two formats are given and a file
.Ar %N.%S
exists in the current directory, the first format is used;
otherwise, the second format is used.
.It Cm style Ns = Ns Ar style.css
The file
.Ar style.css
is used for an external style-sheet.
This must be a valid absolute or
relative URI.
.It Cm tag Ns Op = Ns Ar term
Same syntax and semantics as for
.Sx ASCII Output .
This is implemented by passing a
.Ic file://
URI ending in a fragment identifier to the pager
rather than passing merely a file name.
When using this argument, use a pager supporting such URIs, for example
.Bd -literal -offset 3n
MANPAGER='lynx -force_html' man -T html -O tag=MANPAGER man
MANPAGER='w3m -T text/html' man -T html -O tag=toc mandoc
.Ed
.Pp
Consequently, for HTML output, this argument does not work with
.Xr more 1
or
.Xr less 1 .
For example,
.Ql MANPAGER=less man -T html -O tag=toc mandoc
does not work because
.Xr less 1
does not support
.Ic file://
URIs.
.It Cm toc
If an input file contains at least two non-standard sections,
print a table of contents near the beginning of the output.
.El
.Ss Locale Output
By default,
.Nm
automatically selects UTF-8 or ASCII output according to the current
.Xr locale 1 .
If any of the environment variables
.Ev LC_ALL ,
.Ev LC_CTYPE ,
or
.Ev LANG
are set and the first one that is set
selects the UTF-8 character encoding, it produces
.Sx UTF-8 Output ;
otherwise, it falls back to
.Sx ASCII Output .
This output mode can also be selected explicitly with
.Fl T Cm locale .
.Ss Man Output
Use
.Fl T Cm man
to translate
.Xr mdoc 7
input into
.Xr man 7
output format.
This is useful for distributing manual sources to legacy systems
lacking
.Xr mdoc 7
formatters.
Embedded
.Xr eqn 7
and
.Xr tbl 7
code is not supported.
.Pp
If the input format of a file is
.Xr man 7 ,
the input is copied to the output.
The parser is also run, and as usual, the
.Fl W
level controls which
.Sx DIAGNOSTICS
are displayed before copying the input to the output.
.Ss Markdown Output
Use
.Fl T Cm markdown
to translate
.Xr mdoc 7
input to the markdown format conforming to
.Lk https://daringfireball.net/projects/markdown/syntax.text\
 "John Gruber's 2004 specification" .
The output also almost conforms to the
.Lk https://commonmark.org/ CommonMark
specification.
.Pp
The character set used for the markdown output is ASCII.
Non-ASCII characters are encoded as HTML entities.
Since that is not possible in literal font contexts, because these
are rendered as code spans and code blocks in the markdown output,
non-ASCII characters are transliterated to ASCII approximations in
these contexts.
.Pp
Markdown is a very weak markup language, so all semantic markup is
lost, and even part of the presentational markup may be lost.
Do not use this as an intermediate step in converting to HTML;
instead, use
.Fl T Cm html
directly.
.Pp
The
.Xr man 7 ,
.Xr tbl 7 ,
and
.Xr eqn 7
input languages are not supported by
.Fl T Cm markdown
output mode.
.Ss PDF Output
PDF-1.1 output may be generated by
.Fl T Cm pdf .
See
.Sx PostScript Output
for
.Fl O
arguments and defaults.
.Ss PostScript Output
PostScript
.Qq Adobe-3.0
Level-2 pages may be generated by
.Fl T Cm ps .
Output pages default to letter sized and are rendered in the Times font
family, 11-point.
Margins are calculated as 1/9 the page length and width.
Line-height is 1.4m.
.Pp
Special characters are rendered as in
.Sx ASCII Output .
.Pp
The following
.Fl O
arguments are accepted:
.Bl -tag -width Ds
.It Cm paper Ns = Ns Ar name
The paper size
.Ar name
may be one of
.Ar a3 ,
.Ar a4 ,
.Ar a5 ,
.Ar legal ,
or
.Ar letter .
You may also manually specify dimensions as
.Ar NNxNN ,
width by height in millimetres.
If an unknown value is encountered,
.Ar letter
is used.
.El
.Ss UTF-8 Output
Use
.Fl T Cm utf8
to force text output in UTF-8 multi-byte character encoding,
ignoring the
.Xr locale 1
settings in the environment.
See
.Sx ASCII Output
regarding font styles and
.Fl O
arguments.
.Pp
On operating systems lacking locale or wide character support, and
on those where the internal character representation is not UCS-4,
.Nm
always falls back to
.Sx ASCII Output .
.Ss Syntax tree output
Use
.Fl T Cm tree
to show a human readable representation of the syntax tree.
It is useful for debugging the source code of manual pages.
The exact format is subject to change, so don't write parsers for it.
.Pp
The first paragraph shows meta data found in the
.Xr mdoc 7
prologue, on the
.Xr man 7
.Ic \&TH
line, or the fallbacks used.
.Pp
In the tree dump, each output line shows one syntax tree node.
Child nodes are indented with respect to their parent node.
The columns are:
.Pp
.Bl -enum -compact
.It
For macro nodes, the macro name; for text and
.Xr tbl 7
nodes, the content.
There is a special format for
.Xr eqn 7
nodes.
.It
Node type (text, elem, block, head, body, body-end, tail, tbl, eqn).
.It
Flags:
.Bl -dash -compact
.It
An opening parenthesis if the node is an opening delimiter.
.It
An asterisk if the node starts a new input line.
.It
The input line number (starting at one).
.It
A colon.
.It
The input column number (starting at one).
.It
A closing parenthesis if the node is a closing delimiter.
.It
A full stop if the node ends a sentence.
.It
BROKEN if the node is a block broken by another block.
.It
NOSRC if the node is not in the input file,
but automatically generated from macros.
.It
NOPRT if the node is not supposed to generate output
for any output format.
.El
.El
.Pp
The following
.Fl O
argument is accepted:
.Bl -tag -width Ds
.It Cm noval
Skip validation and show the unvalidated syntax tree.
This can help to find out whether a given behaviour is caused by
the parser or by the validator.
Meta data is not available in this case.
.El
.Sh ENVIRONMENT
.Bl -tag -width MANPAGER
.It Ev LC_CTYPE
The character encoding
.Xr locale 1 .
When
.Sx Locale Output
is selected, it decides whether to use ASCII or UTF-8 output format.
It never affects the interpretation of input files.
.It Ev MANPAGER
Any non-empty value of the environment variable
.Ev MANPAGER
is used instead of the standard pagination program,
.Xr less 1 ;
see
.Xr man 1
for details.
Only used if
.Fl a
or
.Fl l
is specified.
.It Ev PAGER
Specifies the pagination program to use when
.Ev MANPAGER
is not defined.
If neither PAGER nor MANPAGER is defined,
.Xr less 1
is used.
Only used if
.Fl a
or
.Fl l
is specified.
.El
.Sh EXIT STATUS
The
.Nm
utility exits with one of the following values, controlled by the message
.Ar level
associated with the
.Fl W
option:
.Pp
.Bl -tag -width Ds -compact
.It 0
No base system convention violations, style suggestions, warnings,
or errors occurred, or those that did were ignored because they
were lower than the requested
.Ar level .
.It 1
At least one base system convention violation or style suggestion
occurred, but no warning or error, and
.Fl W Cm base
or
.Fl W Cm style
was specified.
.It 2
At least one warning occurred, but no error, and
.Fl W Cm warning
or a lower
.Ar level
was requested.
.It 3
At least one parsing error occurred,
but no unsupported feature was encountered, and
.Fl W Cm error
or a lower
.Ar level
was requested.
.It 4
At least one unsupported feature was encountered, and
.Fl W Cm unsupp
or a lower
.Ar level
was requested.
.It 5
Invalid command line arguments were specified.
No input files have been read.
.It 6
An operating system error occurred, for example exhaustion
of memory, file descriptors, or process table entries.
Such errors may cause
.Nm
to exit at once, possibly in the middle of parsing or formatting a file.
.El
.Pp
Note that selecting
.Fl T Cm lint
output mode implies
.Fl W Cm all .
.Sh EXAMPLES
To page manuals to the terminal:
.Pp
.Dl $ mandoc -a mandoc.1 man.1 apropos.1 makewhatis.8
.Pp
To produce HTML manuals with
.Pa /usr/share/misc/mandoc.css
as the style-sheet:
.Pp
.Dl $ mandoc \-T html -O style=/usr/share/misc/mandoc.css mdoc.7 > mdoc.7.html
.Pp
To check over a large set of manuals:
.Pp
.Dl $ mandoc \-T lint \(gafind /usr/src -name \e*\e.[1-9]\(ga
.Pp
To produce a series of PostScript manuals for A4 paper:
.Pp
.Dl $ mandoc \-T ps \-O paper=a4 mdoc.7 man.7 > manuals.ps
.Pp
Convert a modern
.Xr mdoc 7
manual to the older
.Xr man 7
format, for use on systems lacking an
.Xr mdoc 7
parser:
.Pp
.Dl $ mandoc \-T man foo.mdoc > foo.man
.Sh DIAGNOSTICS
Messages displayed by
.Nm
follow this format:
.Bd -ragged -offset indent
.Nm :
.Ar file : Ns Ar line : Ns Ar column : level : message : macro arguments
.Pq Ar os
.Ed
.Pp
The first three fields identify the
.Ar file
name,
.Ar line
number, and
.Ar column
number of the input file where the message was triggered.
The line and column numbers start at 1.
Both are omitted for messages referring to an input file as a whole.
All
.Ar level
and
.Ar message
strings are explained below.
The name of the
.Ar macro
triggering the message and its
.Ar arguments
are omitted where meaningless.
The
.Ar os
operating system specifier is omitted for messages that are relevant
for all operating systems.
Fatal messages about invalid command line arguments
or operating system errors, for example when memory is exhausted,
may also omit the
.Ar file
and
.Ar level
fields.
.Pp
Message levels have the following meanings:
.Bl -tag -width "warning"
.It Cm syserr
An operating system error occurred.
There isn't necessarily anything wrong with the input files.
Output may all the same be missing or incomplete.
.It Cm badarg
Invalid command line arguments were specified.
No input files have been read and no output is produced.
.It Cm unsupp
An input file uses unsupported low-level
.Xr roff 7
features.
The output may be incomplete and/or misformatted,
so using GNU troff instead of
.Nm
to process the file may be preferable.
.It Cm error
Indicates a risk of information loss or severe misformatting,
in most cases caused by serious syntax errors.
.It Cm warning
Indicates a risk that the information shown or its formatting
may mismatch the author's intent in minor ways.
Additionally, syntax errors are classified at least as warnings,
even if they do not usually cause misformatting.
.It Cm style
An input file uses dubious or discouraged style.
This is not a complaint about the syntax, and probably neither
formatting nor portability are in danger.
While great care is taken to avoid false positives on the higher
message levels, the
.Cm style
level tries to reduce the probability that issues go unnoticed,
so it may occasionally issue bogus suggestions.
Use your judgement to decide whether any particular
.Cm style
suggestion really justifies a change to the input file.
.It Cm base
A convention used in the base system of a specific operating system
is not adhered to.
These are not markup mistakes, and neither the quality of formatting
nor portability are in danger.
Messages of the
.Cm base
level are printed with the more intuitive
.Cm style
.Ar level
tag.
.El
.Pp
Messages of the
.Cm base ,
.Cm style ,
.Cm warning ,
.Cm error ,
and
.Cm unsupp
levels are hidden unless their level, or a lower level, is requested using a
.Fl W
option or
.Fl T Cm lint
output mode.
.Pp
As indicated below, all
.Cm base
and some
.Cm style
checks are only performed if a specific operating system name occurs
in the arguments of the
.Fl W
command line option, of the
.Ic \&Os
macro, of the
.Fl Ios
command line option, or, if neither are present, in the return value
of the
.Xr uname 3
function.
.Ss Conventions for base system manuals
.Bl -ohang
.It Sy "Mdocdate found"
.Pq mdoc , Nx
The
.Ic \&Dd
macro uses CVS
.Ic Mdocdate
keyword substitution, which is not supported by the
.Nx
base system.
Consider using the conventional
.Dq "Month dd, yyyy"
format instead.
.It Sy "Mdocdate missing"
.Pq mdoc , Ox
The
.Ic \&Dd
macro does not use CVS
.Ic Mdocdate
keyword substitution, but using it is conventionally expected in the
.Ox
base system.
.It Sy "unknown architecture"
.Pq mdoc , Ox , Nx
The third argument of the
.Ic \&Dt
macro does not match any of the architectures this operating system
is running on.
.It Sy "operating system explicitly specified"
.Pq mdoc , Ox , Nx
The
.Ic \&Os
macro has an argument.
In the base system, it is conventionally left blank.
.It Sy "RCS id missing"
.Pq Ox , Nx
The manual page lacks the comment line with the RCS identifier
generated by CVS
.Ic OpenBSD
or
.Ic NetBSD
keyword substitution as conventionally used in these operating systems.
.El
.Ss Style suggestions
.Bl -ohang
.It Sy "legacy man(7) date format"
.Pq mdoc
The
.Ic \&Dd
macro uses the legacy
.Xr man 7
date format
.Dq yyyy-dd-mm .
Consider using the conventional
.Xr mdoc 7
date format
.Dq "Month dd, yyyy"
instead.
.It Sy "normalizing date format to" : No ...
.Pq mdoc , man
The
.Ic \&Dd
or
.Ic \&TH
macro provides an abbreviated month name or a day number with a
leading zero.
In the formatted output, the month name is written out in full
and the leading zero is omitted.
.It Sy "lower case character in document title"
.Pq mdoc , man
The title is still used as given in the
.Ic \&Dt
or
.Ic \&TH
macro.
.It Sy "duplicate RCS id"
A single manual page contains two copies of the RCS identifier for
the same operating system.
Consider deleting the later instance and moving the first one up
to the top of the page.
.It Sy "possible typo in section name"
.Pq mdoc
Fuzzy string matching revealed that the argument of an
.Ic \&Sh
macro is similar, but not identical to a standard section name.
.It Sy "unterminated quoted argument"
.Pq roff
Macro arguments can be enclosed in double quote characters
such that space characters and macro names contained in the quoted
argument need not be escaped.
The closing quote of the last argument of a macro can be omitted.
However, omitting it is not recommended because it makes the code
harder to read.
.It Sy "useless macro"
.Pq mdoc
A
.Ic \&Bt ,
.Ic \&Tn ,
or
.Ic \&Ud
macro was found.
Simply delete it: it serves no useful purpose.
.It Sy "consider using OS macro"
.Pq mdoc
A string was found in plain text or in a
.Ic \&Bx
macro that could be represented using
.Ic \&Ox ,
.Ic \&Nx ,
.Ic \&Fx ,
or
.Ic \&Dx .
.It Sy "errnos out of order"
.Pq mdoc, Nx
The
.Ic \&Er
items in a
.Ic \&Bl
list are not in alphabetical order.
.It Sy "duplicate errno"
.Pq mdoc, Nx
A
.Ic \&Bl
list contains two consecutive
.Ic \&It
entries describing the same
.Ic \&Er
number.
.It Sy "referenced manual not found"
.Pq mdoc
An
.Ic \&Xr
macro references a manual page that was not found.
When running with
.Fl W Cm base ,
the search is restricted to the base system, by default to
.Pa /usr/share/man : Ns Pa /usr/X11R6/man .
This path can be configured at compile time using the
.Dv MANPATH_BASE
preprocessor macro.
When running with
.Fl W Cm style ,
the search is done along the full search path as described in the
.Xr man 1
manual page, respecting the
.Fl m
and
.Fl M
command line options, the
.Ev MANPATH
environment variable, the
.Xr man.conf 5
file and falling back to the default of
.Pa /usr/share/man : Ns Pa /usr/X11R6/man : Ns Pa /usr/local/man ,
also configurable at compile time using the
.Dv MANPATH_DEFAULT
preprocessor macro.
.It Sy "trailing delimiter"
.Pq mdoc
The last argument of an
.Ic \&Ex , \&Fo , \&Nd , \&Nm , \&Os , \&Sh , \&Ss , \&St ,
or
.Ic \&Sx
macro ends with a trailing delimiter.
This is usually bad style and often indicates typos.
Most likely, the delimiter can be removed.
.It Sy "no blank before trailing delimiter"
.Pq mdoc
The last argument of a macro that supports trailing delimiter
arguments is longer than one byte and ends with a trailing delimiter.
Consider inserting a blank such that the delimiter becomes a separate
argument, thus moving it out of the scope of the macro.
.It Sy "fill mode already enabled, skipping"
.Pq man
A
.Ic \&fi
request occurs even though the document is still in fill mode,
or already switched back to fill mode.
It has no effect.
.It Sy "fill mode already disabled, skipping"
.Pq man
An
.Ic \&nf
request occurs even though the document already switched to no-fill mode
and did not switch back to fill mode yet.
It has no effect.
.It Sy "input text line longer than 80 bytes"
Consider breaking the input text line
at one of the blank characters before column 80.
.It Sy "verbatim \(dq--\(dq, maybe consider using \e(em"
.Pq mdoc
Even though the ASCII output device renders an em-dash as
.Qq \-\- ,
that is not a good way to write it in an input file
because it renders poorly on all other output devices.
.It Sy "function name without markup"
.Pq mdoc
A word followed by an empty pair of parentheses occurs on a text line.
Consider using an
.Ic \&Fn
or
.Ic \&Xr
macro.
.It Sy "whitespace at end of input line"
.Pq mdoc , man , roff
Whitespace at the end of input lines is almost never semantically
significant \(em but in the odd case where it might be, it is
extremely confusing when reviewing and maintaining documents.
.It Sy "bad comment style"
.Pq roff
Comment lines start with a dot, a backslash, and a double-quote character.
The
.Nm
utility treats the line as a comment line even without the backslash,
but leaving out the backslash might not be portable.
.El
.Ss Warnings related to the document prologue
.Bl -ohang
.It Sy "missing manual title, using UNTITLED"
.Pq mdoc
A
.Ic \&Dt
macro has no arguments, or there is no
.Ic \&Dt
macro before the first non-prologue macro.
.It Sy "missing manual title, using \(dq\(dq"
.Pq man
There is no
.Ic \&TH
macro, or it has no arguments.
.It Sy "missing manual section, using \(dq\(dq"
.Pq mdoc , man
A
.Ic \&Dt
or
.Ic \&TH
macro lacks the mandatory section argument.
.It Sy "unknown manual section"
.Pq mdoc
The section number in a
.Ic \&Dt
line is invalid, but still used.
.It Sy "filename/section mismatch"
.Pq mdoc , man
The name of the input file being processed is known and its file
name extension starts with a non-zero digit, but the
.Ic \&Dt
or
.Ic \&TH
macro contains a
.Ar section
argument that starts with a different non-zero digit.
The
.Ar section
argument is used as provided anyway.
Consider checking whether the file name or the argument need a correction.
.It Sy "missing date, using \(dq\(dq"
.Pq mdoc, man
The document was parsed as
.Xr mdoc 7
and it has no
.Ic \&Dd
macro, or the
.Ic \&Dd
macro has no arguments or only empty arguments;
or the document was parsed as
.Xr man 7
and it has no
.Ic \&TH
macro, or the
.Ic \&TH
macro has less than three arguments or its third argument is empty.
.It Sy "cannot parse date, using it verbatim"
.Pq mdoc , man
The date given in a
.Ic \&Dd
or
.Ic \&TH
macro does not follow the conventional format.
.It Sy "date in the future, using it anyway"
.Pq mdoc , man
The date given in a
.Ic \&Dd
or
.Ic \&TH
macro is more than a day ahead of the current system
.Xr time 3 .
.It Sy "missing Os macro, using \(dq\(dq"
.Pq mdoc
The default or current system is not shown in this case.
.It Sy "late prologue macro"
.Pq mdoc
A
.Ic \&Dd
or
.Ic \&Os
macro occurs after some non-prologue macro, but still takes effect.
.It Sy "prologue macros out of order"
.Pq mdoc
The prologue macros are not given in the conventional order
.Ic \&Dd ,
.Ic \&Dt ,
.Ic \&Os .
All three macros are used even when given in another order.
.El
.Ss Warnings regarding document structure
.Bl -ohang
.It Sy ".so is fragile, better use ln(1)"
.Pq roff
Including files only works when the parser program runs with the correct
current working directory.
.It Sy "no document body"
.Pq mdoc , man
The document body contains neither text nor macros.
An empty document is shown, consisting only of a header and a footer line.
.It Sy "content before first section header"
.Pq mdoc , man
Some macros or text precede the first
.Ic \&Sh
or
.Ic \&SH
section header.
The offending macros and text are parsed and added to the top level
of the syntax tree, outside any section block.
.It Sy "first section is not NAME"
.Pq mdoc
The argument of the first
.Ic \&Sh
macro is not
.Sq NAME .
This may confuse
.Xr makewhatis 8
and
.Xr apropos 1 .
.It Sy "NAME section without Nm before Nd"
.Pq mdoc
The NAME section does not contain any
.Ic \&Nm
child macro before the first
.Ic \&Nd
macro.
.It Sy "NAME section without description"
.Pq mdoc
The NAME section lacks the mandatory
.Ic \&Nd
child macro.
.It Sy "description not at the end of NAME"
.Pq mdoc
The NAME section does contain an
.Ic \&Nd
child macro, but other content follows it.
.It Sy "bad NAME section content"
.Pq mdoc
The NAME section contains plain text or macros other than
.Ic \&Nm
and
.Ic \&Nd .
.It Sy "missing comma before name"
.Pq mdoc
The NAME section contains an
.Ic \&Nm
macro that is neither the first one nor preceded by a comma.
.It Sy "missing description line, using \(dq\(dq"
.Pq mdoc
The
.Ic \&Nd
macro lacks the required argument.
The title line of the manual will end after the dash.
.It Sy "description line outside NAME section"
.Pq mdoc
An
.Ic \&Nd
macro appears outside the NAME section.
The arguments are printed anyway and the following text is used for
.Xr apropos 1 ,
but none of that behaviour is portable.
.It Sy "sections out of conventional order"
.Pq mdoc
A standard section occurs after another section it usually precedes.
All section titles are used as given,
and the order of sections is not changed.
.It Sy "duplicate section title"
.Pq mdoc
The same standard section title occurs more than once.
.It Sy "unexpected section"
.Pq mdoc
A standard section header occurs in a section of the manual
where it normally isn't useful.
.It Sy "cross reference to self"
.Pq mdoc
An
.Ic \&Xr
macro refers to a name and section matching the section of the present
manual page and a name mentioned in an
.Ic \&Nm
macro in the NAME or SYNOPSIS section, or in an
.Ic \&Fn
or
.Ic \&Fo
macro in the SYNOPSIS.
Consider using
.Ic \&Nm
or
.Ic \&Fn
instead of
.Ic \&Xr .
.It Sy "unusual Xr order"
.Pq mdoc
In the SEE ALSO section, an
.Ic \&Xr
macro with a lower section number follows one with a higher number,
or two
.Ic \&Xr
macros referring to the same section are out of alphabetical order.
.It Sy "unusual Xr punctuation"
.Pq mdoc
In the SEE ALSO section, punctuation between two
.Ic \&Xr
macros differs from a single comma, or there is trailing punctuation
after the last
.Ic \&Xr
macro.
.It Sy "AUTHORS section without An macro"
.Pq mdoc
An AUTHORS sections contains no
.Ic \&An
macros, or only empty ones.
Probably, there are author names lacking markup.
.El
.Ss "Warnings related to macros and nesting"
.Bl -ohang
.It Sy "obsolete macro"
.Pq mdoc
See the
.Xr mdoc 7
manual for replacements.
.It Sy "macro neither callable nor escaped"
.Pq mdoc
The name of a macro that is not callable appears on a macro line.
It is printed verbatim.
If the intention is to call it, move it to its own input line;
otherwise, escape it by prepending
.Sq \e& .
.It Sy "skipping paragraph macro"
In
.Xr mdoc 7
documents, this happens
.Bl -dash -compact
.It
at the beginning and end of sections and subsections
.It
right before non-compact lists and displays
.It
at the end of items in non-column, non-compact lists
.It
and for multiple consecutive paragraph macros.
.El
In
.Xr man 7
documents, it happens
.Bl -dash -compact
.It
for empty
.Ic \&P ,
.Ic \&PP ,
and
.Ic \&LP
macros
.It
for
.Ic \&IP
macros having neither head nor body arguments
.It
for
.Ic \&br
or
.Ic \&sp
right after
.Ic \&SH
or
.Ic \&SS
.El
.It Sy "moving paragraph macro out of list"
.Pq mdoc
A list item in a
.Ic \&Bl
list contains a trailing paragraph macro.
The paragraph macro is moved after the end of the list.
.It Sy "skipping no-space macro"
.Pq mdoc
An input line begins with an
.Ic \&Ns
macro, or the next argument after an
.Ic \&Ns
macro is an isolated closing delimiter.
The macro is ignored.
.It Sy "blocks badly nested"
.Pq mdoc
If two blocks intersect, one should completely contain the other.
Otherwise, rendered output is likely to look strange in any output
format, and rendering in SGML-based output formats is likely to be
outright wrong because such languages do not support badly nested
blocks at all.
Typical examples of badly nested blocks are
.Qq Ic \&Ao \&Bo \&Ac \&Bc
and
.Qq Ic \&Ao \&Bq \&Ac .
In these examples,
.Ic \&Ac
breaks
.Ic \&Bo
and
.Ic \&Bq ,
respectively.
.It Sy "nested displays are not portable"
.Pq mdoc
A
.Ic \&Bd ,
.Ic \&D1 ,
or
.Ic \&Dl
display occurs nested inside another
.Ic \&Bd
display.
This works with
.Nm ,
but fails with most other implementations.
.It Sy "moving content out of list"
.Pq mdoc
A
.Ic \&Bl
list block contains text or macros before the first
.Ic \&It
macro.
The offending children are moved before the beginning of the list.
.It Sy "first macro on line"
Inside a
.Ic \&Bl Fl column
list, a
.Ic \&Ta
macro occurs as the first macro on a line, which is not portable.
.It Sy "line scope broken"
.Pq man
While parsing the next-line scope of the previous macro,
another macro is found that prematurely terminates the previous one.
The previous, interrupted macro is deleted from the parse tree.
.El
.Ss "Warnings related to missing arguments"
.Bl -ohang
.It Sy "skipping empty request"
.Pq roff , eqn
The macro name is missing from a macro definition request,
or an
.Xr eqn 7
control statement or operation keyword lacks its required argument.
.It Sy "conditional request controls empty scope"
.Pq roff
A conditional request is only useful if any of the following
follows it on the same logical input line:
.Bl -dash -compact
.It
The
.Sq \e{
keyword to open a multi-line scope.
.It
A request or macro or some text, resulting in a single-line scope.
.It
The immediate end of the logical line without any intervening whitespace,
resulting in next-line scope.
.El
Here, a conditional request is followed by trailing whitespace only,
and there is no other content on its logical input line.
Note that it doesn't matter whether the logical input line is split
across multiple physical input lines using
.Sq \e
line continuation characters.
This is one of the rare cases
where trailing whitespace is syntactically significant.
The conditional request controls a scope containing whitespace only,
so it is unlikely to have a significant effect,
except that it may control a following
.Ic \&el
clause.
.It Sy "skipping empty macro"
.Pq mdoc
The indicated macro has no arguments and hence no effect.
.It Sy "empty block"
.Pq mdoc , man
A
.Ic \&Bd ,
.Ic \&Bk ,
.Ic \&Bl ,
.Ic \&D1 ,
.Ic \&Dl ,
.Ic \&MT ,
.Ic \&RS ,
or
.Ic \&UR
block contains nothing in its body and will produce no output.
.It Sy "empty argument, using 0n"
.Pq mdoc
The required width is missing after
.Ic \&Bd
or
.Ic \&Bl
.Fl offset
or
.Fl width .
.It Sy "missing display type, using -ragged"
.Pq mdoc
The
.Ic \&Bd
macro is invoked without the required display type.
.It Sy "list type is not the first argument"
.Pq mdoc
In a
.Ic \&Bl
macro, at least one other argument precedes the type argument.
The
.Nm
utility copes with any argument order, but some other
.Xr mdoc 7
implementations do not.
.It Sy "missing -width in -tag list, using 8n"
.Pq mdoc
Every
.Ic \&Bl
macro having the
.Fl tag
argument requires
.Fl width ,
too.
.It Sy "missing utility name, using \(dq\(dq"
.Pq mdoc
The
.Ic \&Ex Fl std
macro is called without an argument before
.Ic \&Nm
has first been called with an argument.
.It Sy "missing function name, using \(dq\(dq"
.Pq mdoc
The
.Ic \&Fo
macro is called without an argument.
No function name is printed.
.It Sy "empty head in list item"
.Pq mdoc
In a
.Ic \&Bl
.Fl diag ,
.Fl hang ,
.Fl inset ,
.Fl ohang ,
or
.Fl tag
list, an
.Ic \&It
macro lacks the required argument.
The item head is left empty.
.It Sy "empty list item"
.Pq mdoc
In a
.Ic \&Bl
.Fl bullet ,
.Fl dash ,
.Fl enum ,
or
.Fl hyphen
list, an
.Ic \&It
block is empty.
An empty list item is shown.
.It Sy "missing argument, using next line"
.Pq mdoc
An
.Ic \&It
macro in a
.Ic \&Bd Fl column
list has no arguments.
While
.Nm
uses the text or macros of the following line, if any, for the cell,
other formatters may misformat the list.
.It Sy "missing font type, using \efR"
.Pq mdoc
A
.Ic \&Bf
macro has no argument.
It switches to the default font.
.It Sy "unknown font type, using \efR"
.Pq mdoc
The
.Ic \&Bf
argument is invalid.
The default font is used instead.
.It Sy "nothing follows prefix"
.Pq mdoc
A
.Ic \&Pf
macro has no argument, or only one argument and no macro follows
on the same input line.
This defeats its purpose; in particular, spacing is not suppressed
before the text or macros following on the next input line.
.It Sy "empty reference block"
.Pq mdoc
An
.Ic \&Rs
macro is immediately followed by an
.Ic \&Re
macro on the next input line.
Such an empty block does not produce any output.
.It Sy "missing section argument"
.Pq mdoc
An
.Ic \&Xr
macro lacks its second, section number argument.
The first argument, i.e. the name, is printed, but without subsequent
parentheses.
.It Sy "missing -std argument, adding it"
.Pq mdoc
An
.Ic \&Ex
or
.Ic \&Rv
macro lacks the required
.Fl std
argument.
The
.Nm
utility assumes
.Fl std
even when it is not specified, but other implementations may not.
.It Sy "missing option string, using \(dq\(dq"
.Pq man
The
.Ic \&OP
macro is invoked without any argument.
An empty pair of square brackets is shown.
.It Sy "missing resource identifier, using \(dq\(dq"
.Pq man
The
.Ic \&MT
or
.Ic \&UR
macro is invoked without any argument.
An empty pair of angle brackets is shown.
.It Sy "missing eqn box, using \(dq\(dq"
.Pq eqn
A diacritic mark or a binary operator is found,
but there is nothing to the left of it.
An empty box is inserted.
.El
.Ss "Warnings related to bad macro arguments"
.Bl -ohang
.It Sy "duplicate argument"
.Pq mdoc
A
.Ic \&Bd
or
.Ic \&Bl
macro has more than one
.Fl compact ,
more than one
.Fl offset ,
or more than one
.Fl width
argument.
All but the last instances of these arguments are ignored.
.It Sy "skipping duplicate argument"
.Pq mdoc
An
.Ic \&An
macro has more than one
.Fl split
or
.Fl nosplit
argument.
All but the first of these arguments are ignored.
.It Sy "skipping duplicate display type"
.Pq mdoc
A
.Ic \&Bd
macro has more than one type argument; the first one is used.
.It Sy "skipping duplicate list type"
.Pq mdoc
A
.Ic \&Bl
macro has more than one type argument; the first one is used.
.It Sy "skipping -width argument"
.Pq mdoc
A
.Ic \&Bl
.Fl column ,
.Fl diag ,
.Fl ohang ,
.Fl inset ,
or
.Fl item
list has a
.Fl width
argument.
That has no effect.
.It Sy "wrong number of cells"
In a line of a
.Ic \&Bl Fl column
list, the number of tabs or
.Ic \&Ta
macros is less than the number expected from the list header line
or exceeds the expected number by more than one.
Missing cells remain empty, and all cells exceeding the number of
columns are joined into one single cell.
.It Sy "unknown AT&T UNIX version"
.Pq mdoc
An
.Ic \&At
macro has an invalid argument.
It is used verbatim, with
.Qq "AT&T UNIX "
prefixed to it.
.It Sy "comma in function argument"
.Pq mdoc
An argument of an
.Ic \&Fa
or
.Ic \&Fn
macro contains a comma; it should probably be split into two arguments.
.It Sy "parenthesis in function name"
.Pq mdoc
The first argument of an
.Ic \&Fc
or
.Ic \&Fn
macro contains an opening or closing parenthesis; that's probably wrong,
parentheses are added automatically.
.It Sy "unknown library name"
.Pq mdoc, not on Ox
An
.Ic \&Lb
macro has an unknown name argument and will be rendered as
.Qq library Dq Ar name .
.It Sy "invalid content in Rs block"
.Pq mdoc
An
.Ic \&Rs
block contains plain text or non-% macros.
The bogus content is left in the syntax tree.
Formatting may be poor.
.It Sy "invalid Boolean argument"
.Pq mdoc
An
.Ic \&Sm
macro has an argument other than
.Cm on
or
.Cm off .
The invalid argument is moved out of the macro, which leaves the macro
empty, causing it to toggle the spacing mode.
.It Sy "argument contains two font escapes"
.Pq roff
The second argument of a
.Ic char
request contains more than one font escape sequence.
A wrong font may remain active after using the character.
.It Sy "unknown font, skipping request"
.Pq man , tbl
A
.Xr roff 7
.Ic \&ft
request or a
.Xr tbl 7
.Ic \&f
layout modifier has an unknown
.Ar font
argument.
.It Sy "ignoring distance argument"
.Pq roff
In addition to the margin character, an
.Ic \&mc
request has a second argument supposed to represent a distance, but the
.Nm
implementation of
.Ic \&mc
always ignores the second argument.
.It Sy "odd number of characters in request"
.Pq roff
A
.Ic \&tr
request contains an odd number of characters.
The last character is mapped to the blank character.
.El
.Ss "Warnings related to plain text"
.Bl -ohang
.It Sy "blank line in fill mode, using .sp"
.Pq mdoc
The meaning of blank input lines is only well-defined in non-fill mode:
In fill mode, line breaks of text input lines are not supposed to be
significant.
However, for compatibility with groff, blank lines in fill mode
are formatted like
.Ic \&sp
requests.
To request a paragraph break, use
.Ic \&Pp
instead of a blank line.
.It Sy "tab in filled text"
.Pq mdoc , man
The meaning of tab characters is only well-defined in non-fill mode:
In fill mode, whitespace is not supposed to be significant
on text input lines.
As an implementation dependent choice, tab characters on text lines
are passed through to the formatters in any case.
Given that the text before the tab character will be filled,
it is hard to predict which tab stop position the tab will advance to.
.It Sy "new sentence, new line"
.Pq mdoc
A new sentence starts in the middle of a text line.
Start it on a new input line to help formatters produce correct spacing.
.It Sy "invalid escape sequence argument"
.Pq roff
The argument of an escape sequence is of an invalid form.
Invalid escape sequences are ignored.
.It Sy "undefined escape, printing literally"
.Pq roff
In an escape sequence, the first character
right after the leading backslash is invalid.
That character is printed literally,
which is equivalent to ignoring the backslash.
.It Sy "undefined string, using \(dq\(dq"
.Pq roff
If a string is used without being defined before,
its value is implicitly set to the empty string.
However, defining strings explicitly before use
keeps the code more readable.
.El
.Ss "Warnings related to tables"
.Bl -ohang
.It Sy "tbl line starts with span"
.Pq tbl
The first cell in a table layout line is a horizontal span
.Pq Sq Cm s .
Data provided for this cell is ignored, and nothing is printed in the cell.
.It Sy "tbl column starts with span"
.Pq tbl
The first line of a table layout specification
requests a vertical span
.Pq Sq Cm ^ .
Data provided for this cell is ignored, and nothing is printed in the cell.
.It Sy "skipping vertical bar in tbl layout"
.Pq tbl
A table layout specification contains more than two consecutive vertical bars.
A double bar is printed, all additional bars are discarded.
.El
.Ss "Errors related to tables"
.Bl -ohang
.It Sy "non-alphabetic character in tbl options"
.Pq tbl
The table options line contains a character other than a letter,
blank, or comma where the beginning of an option name is expected.
The character is ignored.
.It Sy "skipping unknown tbl option"
.Pq tbl
The table options line contains a string of letters that does not
match any known option name.
The word is ignored.
.It Sy "missing tbl option argument"
.Pq tbl
A table option that requires an argument is not followed by an
opening parenthesis, or the opening parenthesis is immediately
followed by a closing parenthesis.
The option is ignored.
.It Sy "wrong tbl option argument size"
.Pq tbl
A table option argument contains an invalid number of characters.
Both the option and the argument are ignored.
.It Sy "empty tbl layout"
.Pq tbl
A table layout specification is completely empty,
specifying zero lines and zero columns.
As a fallback, a single left-justified column is used.
.It Sy "invalid character in tbl layout"
.Pq tbl
A table layout specification contains a character that can neither
be interpreted as a layout key character nor as a layout modifier,
or a modifier precedes the first key.
The invalid character is discarded.
.It Sy "unmatched parenthesis in tbl layout"
.Pq tbl
A table layout specification contains an opening parenthesis,
but no matching closing parenthesis.
The rest of the input line, starting from the parenthesis, has no effect.
.It Sy "ignoring excessive spacing in tbl layout"
.Pq tbl
A spacing modifier in a table layout is unreasonably large.
The default spacing of 3n is used instead.
.It Sy "tbl without any data cells"
.Pq tbl
A table does not contain any data cells.
It will probably produce no output.
.It Sy "ignoring data in spanned tbl cell"
.Pq tbl
A table cell is marked as a horizontal span
.Pq Sq Cm s
or vertical span
.Pq Sq Cm ^
in the table layout, but it contains data.
The data is ignored.
.It Sy "ignoring extra tbl data cells"
.Pq tbl
A data line contains more cells than the corresponding layout line.
The data in the extra cells is ignored.
.It Sy "data block open at end of tbl"
.Pq tbl
A data block is opened with
.Cm T{ ,
but never closed with a matching
.Cm T} .
The remaining data lines of the table are all put into one cell,
and any remaining cells stay empty.
.El
.Ss "Errors related to roff, mdoc, and man code"
.Bl -ohang
.It Sy "duplicate prologue macro"
.Pq mdoc
One of the prologue macros occurs more than once.
The last instance overrides all previous ones.
.It Sy "skipping late title macro"
.Pq mdoc
The
.Ic \&Dt
macro appears after the first non-prologue macro.
Traditional formatters cannot handle this because
they write the page header before parsing the document body.
Even though this technical restriction does not apply to
.Nm ,
traditional semantics is preserved.
The late macro is discarded including its arguments.
.It Sy "input stack limit exceeded, infinite loop?"
.Pq roff
Explicit recursion limits are implemented for the following features,
in order to prevent infinite loops:
.Bl -dash -compact
.It
expansion of nested escape sequences
including expansion of strings and number registers,
.It
expansion of nested user-defined macros,
.It
and
.Ic \&so
file inclusion.
.El
When a limit is hit, the output is incorrect, typically losing
some content, but the parser can continue.
.It Sy "skipping bad character"
.Pq mdoc , man , roff
The input file contains a byte that is not a printable
.Xr ascii 7
character.
The message mentions the character number.
The offending byte is replaced with a question mark
.Pq Sq \&? .
Consider editing the input file to replace the byte with an ASCII
transliteration of the intended character.
.It Sy "skipping unknown macro"
.Pq mdoc , man , roff
The first identifier on a request or macro line is neither recognized as a
.Xr roff 7
request, nor as a user-defined macro, nor, respectively, as an
.Xr mdoc 7
or
.Xr man 7
macro.
It may be mistyped or unsupported.
The request or macro is discarded including its arguments.
.It Sy "skipping request outside macro"
.Pq roff
A
.Ic shift
or
.Ic return
request occurs outside any macro definition and has no effect.
.It Sy "skipping insecure request"
.Pq roff
An input file attempted to run a shell command
or to read or write an external file.
Such attempts are denied for security reasons.
.It Sy "skipping item outside list"
.Pq mdoc , eqn
An
.Ic \&It
macro occurs outside any
.Ic \&Bl
list, or an
.Xr eqn 7
.Ic above
delimiter occurs outside any pile.
It is discarded including its arguments.
.It Sy "skipping column outside column list"
.Pq mdoc
A
.Ic \&Ta
macro occurs outside any
.Ic \&Bl Fl column
block.
It is discarded including its arguments.
.It Sy "skipping end of block that is not open"
.Pq mdoc , man , eqn , tbl , roff
Various syntax elements can only be used to explicitly close blocks
that have previously been opened.
An
.Xr mdoc 7
block closing macro, a
.Xr man 7
.Ic \&ME , \&RE
or
.Ic \&UE
macro, an
.Xr eqn 7
right delimiter or closing brace, or the end of an equation, table, or
.Xr roff 7
conditional request is encountered but no matching block is open.
The offending request or macro is discarded.
.It Sy "fewer RS blocks open, skipping"
.Pq man
The
.Ic \&RE
macro is invoked with an argument, but less than the specified number of
.Ic \&RS
blocks is open.
The
.Ic \&RE
macro is discarded.
.It Sy "inserting missing end of block"
.Pq mdoc , tbl
Various
.Xr mdoc 7
macros as well as tables require explicit closing by dedicated macros.
A block that doesn't support bad nesting
ends before all of its children are properly closed.
The open child nodes are closed implicitly.
.It Sy "appending missing end of block"
.Pq mdoc , man , eqn , tbl , roff
At the end of the document, an explicit
.Xr mdoc 7
block, a
.Xr man 7
next-line scope or
.Ic \&MT , \&RS
or
.Ic \&UR
block, an equation, table, or
.Xr roff 7
conditional or ignore block is still open.
The open block is closed implicitly.
.It Sy "escaped character not allowed in a name"
.Pq roff
Macro, string and register identifiers consist of printable,
non-whitespace ASCII characters.
Escape sequences and characters and strings expressed in terms of them
cannot form part of a name.
The first argument of an
.Ic \&am ,
.Ic \&as ,
.Ic \&de ,
.Ic \&ds ,
.Ic \&nr ,
or
.Ic \&rr
request, or any argument of an
.Ic \&rm
request, or the name of a request or user defined macro being called,
is terminated by an escape sequence.
In the cases of
.Ic \&as ,
.Ic \&ds ,
and
.Ic \&nr ,
the request has no effect at all.
In the cases of
.Ic \&am ,
.Ic \&de ,
.Ic \&rr ,
and
.Ic \&rm ,
what was parsed up to this point is used as the arguments to the request,
and the rest of the input line is discarded including the escape sequence.
When parsing for a request or a user-defined macro name to be called,
only the escape sequence is discarded.
The characters preceding it are used as the request or macro name,
the characters following it are used as the arguments to the request or macro.
.It Sy "using macro argument outside macro"
.Pq roff
The escape sequence \e$ occurs outside any macro definition
and expands to the empty string.
.It Sy "argument number is not numeric"
.Pq roff
The argument of the escape sequence \e$ is not a digit;
the escape sequence expands to the empty string.
.It Sy "negative argument, using 0"
.Pq roff
A
.Ic \&shift
request has a negative argument
or an argument that is negative due to integer overflow.
Macro argument numbering remains unchanged.
.It Sy "NOT IMPLEMENTED: Bd -file"
.Pq mdoc
For security reasons, the
.Ic \&Bd
macro does not support the
.Fl file
argument.
By requesting the inclusion of a sensitive file, a malicious document
might otherwise trick a privileged user into inadvertently displaying
the file on the screen, revealing the file content to bystanders.
The argument is ignored including the file name following it.
.It Sy "skipping display without arguments"
.Pq mdoc
A
.Ic \&Bd
block macro does not have any arguments.
The block is discarded, and the block content is displayed in
whatever mode was active before the block.
.It Sy "missing list type, using -item"
.Pq mdoc
A
.Ic \&Bl
macro fails to specify the list type.
.It Sy "argument is not numeric, using 1"
.Pq roff
The argument of a
.Ic \&ce
request is not a number.
.It Sy "argument is not a character"
.Pq roff
The first argument of a
.Ic char
request is neither a single ASCII character
nor a single character escape sequence.
The request is ignored including all its arguments.
.It Sy "skipping unusable escape sequence"
.Pq roff
The first argument of an
.Ic mc
request is neither a single ASCII character
nor a single character escape sequence.
All arguments are ignored and printing of a margin character is disabled.
.It Sy "missing manual name, using \(dq\(dq"
.Pq mdoc
The first call to
.Ic \&Nm ,
or any call in the NAME section, lacks the required argument.
.It Sy "uname(3) system call failed, using UNKNOWN"
.Pq mdoc
The
.Ic \&Os
macro is called without arguments, and the
.Xr uname 3
system call failed.
As a workaround,
.Nm
can be compiled with
.Sm off
.Fl D Cm OSNAME=\(dq\e\(dq Ar string Cm \e\(dq\(dq .
.Sm on
.It Sy "unknown standard specifier"
.Pq mdoc
An
.Ic \&St
macro has an unknown argument and is discarded.
.It Sy "skipping request without numeric argument"
.Pq roff , eqn
An
.Ic \&it
request or an
.Xr eqn 7
.Ic \&size
or
.Ic \&gsize
statement has a non-numeric or negative argument or no argument at all.
The invalid request or statement is ignored.
.It Sy "excessive shift"
.Pq roff
The argument of a
.Ic shift
request is larger than the number of arguments of the macro that is
currently being executed.
All macro arguments are deleted and \en(.$ is set to zero.
.It Sy "NOT IMPLEMENTED: .so with absolute path or \(dq..\(dq"
.Pq roff
For security reasons,
.Nm
allows
.Ic \&so
file inclusion requests only with relative paths
and only without ascending to any parent directory.
By requesting the inclusion of a sensitive file, a malicious document
might otherwise trick a privileged user into inadvertently displaying
the file on the screen, revealing the file content to bystanders.
.Nm
only shows the path as it appears behind
.Ic \&so .
.It Sy ".so request failed"
.Pq roff
Servicing a
.Ic \&so
request requires reading an external file, but the file could not be
opened.
.Nm
only shows the path as it appears behind
.Ic \&so .
.It Sy "skipping all arguments"
.Pq mdoc , man , eqn , roff
An
.Xr mdoc 7
.Ic \&Bt ,
.Ic \&Ed ,
.Ic \&Ef ,
.Ic \&Ek ,
.Ic \&El ,
.Ic \&Lp ,
.Ic \&Pp ,
.Ic \&Re ,
.Ic \&Rs ,
or
.Ic \&Ud
macro, an
.Ic \&It
macro in a list that don't support item heads, a
.Xr man 7
.Ic \&LP ,
.Ic \&P ,
or
.Ic \&PP
macro, an
.Xr eqn 7
.Ic \&EQ
or
.Ic \&EN
macro, or a
.Xr roff 7
.Ic \&br ,
.Ic \&fi ,
or
.Ic \&nf
request or
.Sq \&..
block closing request is invoked with at least one argument.
All arguments are ignored.
.It Sy "skipping excess arguments"
.Pq mdoc , man , roff
A macro or request is invoked with too many arguments:
.Bl -dash -offset 2n -width 2n -compact
.It
.Ic \&Fo ,
.Ic \&MT ,
.Ic \&PD ,
.Ic \&RS ,
.Ic \&UR ,
.Ic \&ft ,
or
.Ic \&sp
with more than one argument
.It
.Ic \&An
with another argument after
.Fl split
or
.Fl nosplit
.It
.Ic \&RE
with more than one argument or with a non-integer argument
.It
.Ic \&OP
or a request of the
.Ic \&de
family with more than two arguments
.It
.Ic \&Dt
with more than three arguments
.It
.Ic \&TH
with more than five arguments
.It
.Ic \&Bd ,
.Ic \&Bk ,
or
.Ic \&Bl
with invalid arguments
.El
The excess arguments are ignored.
.El
.Ss "Errors related to escape sequences"
.Bl -ohang
.It Sy "incomplete escape sequence"
.Pq roff
The end of the input line is encountered
while parsing the argument of an escape sequence.
In this case,
.Ic \e*
and
.Ic \en
expand to an empty string,
.Ic \eB
to the digit
.Sq 0 ,
and
.Ic \ew
to the length of the incomplete argument.
All other incomplete escape sequences are ignored.
.It Sy "invalid special character"
.Pq roff
A special character escape sequence is invalid,
for example a Unicode sequence pointing to a surrogate
or beyond the Unicode range, a \e[char...] escape sequence
representing a control character or pointing beyond the
.Vt unsigned char
range, or an invalid variable-length form
of a single-byte character escape sequence, for example writing
.Qq \e[e]
or
.Qq \e[~]
instead of
.Qq \ee
or
.Qq \e~ ,
respectively.
The escape sequence is ignored.
.It Sy "unknown special character"
.Pq roff
The name given in a special character escape sequence is not known to
.Nm .
The escape sequence is ignored.
.It Sy "invalid escape argument delimiter"
.Pq roff
An escape sequence that expects a numerical argument
attempts to employ one of the characters
.Qq " %&()*+-./0123456789:<=>"
as an argument delimiter.
The escape sequence is ignored including the invalid opening delimiter
and the rest of the argument may appear as output text.
While various characters can be used as argument delimiters,
using the apostrophe-quote character
.Pq Sq \(aq
is recommended for readability and robustness.
.El
.Ss Unsupported features
.Bl -ohang
.It Sy "input too large"
.Pq mdoc , man
Currently,
.Nm
cannot handle input files larger than its arbitrary size limit
of 2^31 bytes (2 Gigabytes).
Since useful manuals are always small, this is not a problem in practice.
Parsing is aborted as soon as the condition is detected.
.It Sy "unsupported control character"
.Pq roff
An ASCII control character supported by other
.Xr roff 7
implementations but not by
.Nm
was found in an input file.
It is replaced by a question mark.
.It Sy "unsupported escape sequence"
.Pq roff
An input file contains an escape sequence supported by GNU troff
or Heirloom troff but not by
.Nm ,
and it is likely that this will cause information loss
or considerable misformatting.
.It Sy "unsupported roff request"
.Pq roff
An input file contains a
.Xr roff 7
request supported by GNU troff or Heirloom troff but not by
.Nm ,
and it is likely that this will cause information loss
or considerable misformatting.
.It Sy "eqn delim option in tbl"
.Pq eqn , tbl
The options line of a table defines equation delimiters.
Any equation source code contained in the table will be printed unformatted.
.It Sy "unsupported table layout modifier"
.Pq tbl
A table layout specification contains an
.Sq Cm m
modifier.
The modifier is discarded.
.It Sy "ignoring macro in table"
.Pq tbl , mdoc , man
A table contains an invocation of an
.Xr mdoc 7
or
.Xr man 7
macro or of an undefined macro.
The macro is ignored, and its arguments are handled
as if they were a text line.
.It Sy "skipping tbl in -Tman mode"
.Pq mdoc , tbl
An input file contains the
.Ic \&TS
macro.
This message is only generated in
.Fl T Cm man
output mode, where
.Xr tbl 7
input is not supported.
.It Sy "skipping eqn in -Tman mode"
.Pq mdoc , eqn
An input file contains the
.Ic \&EQ
macro.
This message is only generated in
.Fl T Cm man
output mode, where
.Xr eqn 7
input is not supported.
.El
.Ss Bad command line arguments
.Bl -ohang
.It Sy "bad command line argument"
The argument following one of the
.Fl IKMmOTW
command line options is invalid, or a
.Ar file
given as a command line argument cannot be opened.
.It Sy "duplicate command line argument"
The
.Fl I
command line option was specified twice.
.It Sy "option has a superfluous value"
An argument to the
.Fl O
option has a value but does not accept one.
.It Sy "missing option value"
An argument to the
.Fl O
option has no argument but requires one.
.It Sy "bad option value"
An argument to the
.Fl O
.Cm indent
or
.Cm width
option has an invalid value.
.It Sy "duplicate option value"
The same
.Fl O
option is specified more than once.
.It Sy "no such tag"
The
.Fl O Cm tag
option was specified but the tag was not found in any of the displayed
manual pages.
.It Sy "\-Tmarkdown unsupported for man(7) input"
.Pq man
The
.Fl T Cm markdown
option was specified but an input file uses the
.Xr man 7
language.
No output is produced for that input file.
.El
.Sh SEE ALSO
.Xr apropos 1 ,
.Xr man 1 ,
.Xr eqn 7 ,
.Xr man 7 ,
.Xr mandoc_char 7 ,
.Xr mdoc 7 ,
.Xr roff 7 ,
.Xr tbl 7
.Sh HISTORY
The
.Nm
utility first appeared in
.Ox 4.8 .
The option
.Fl I
appeared in
.Ox 5.2 ,
and
.Fl aCcfhKklMSsw
in
.Ox 5.7 .
.Sh AUTHORS
.An -nosplit
The
.Nm
utility was written by
.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
and is maintained by
.An Ingo Schwarze Aq Mt schwarze@openbsd.org .