===================================================================
RCS file: /cvs/mandoc/mandoc.1,v
retrieving revision 1.50
retrieving revision 1.149
diff -u -p -r1.50 -r1.149
--- mandoc/mandoc.1	2010/01/29 14:39:38	1.50
+++ mandoc/mandoc.1	2015/02/06 09:38:43	1.149
@@ -1,6 +1,7 @@
-.\"	$Id: mandoc.1,v 1.50 2010/01/29 14:39:38 kristaps Exp $
+.\"	$Id: mandoc.1,v 1.149 2015/02/06 09:38:43 schwarze Exp $
 .\"
-.\" Copyright (c) 2009 Kristaps Dzonsons <kristaps@kth.se>
+.\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
+.\" Copyright (c) 2012, 2014, 2015 Ingo Schwarze <schwarze@openbsd.org>
 .\"
 .\" Permission to use, copy, modify, and distribute this software for any
 .\" purpose with or without fee is hereby granted, provided that the above
@@ -14,96 +15,198 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: January 29 2010 $
+.Dd $Mdocdate: February 6 2015 $
 .Dt MANDOC 1
 .Os
-.
-.
 .Sh NAME
 .Nm mandoc
 .Nd format and display UNIX manuals
-.
-.
 .Sh SYNOPSIS
 .Nm mandoc
-.Op Fl f Ns Ar option...
+.Op Fl acfhklV
+.Sm off
+.Op Fl I Cm os Li = Ar name
+.Sm on
+.Op Fl K Ns Ar encoding
 .Op Fl m Ns Ar format
-.Op Fl O Ns Ar option...
+.Op Fl O Ns Ar option
 .Op Fl T Ns Ar output
-.Op Fl V
-.Op Fl W Ns Ar err...
-.Op Ar infile...
-.
-.
+.Op Fl W Ns Ar level
+.Op Ar
 .Sh DESCRIPTION
 The
 .Nm
 utility formats
 .Ux
-manual pages for display.  The arguments are as follows:
-.
+manual pages for display.
+.Pp
+By default,
+.Nm
+reads
+.Xr mdoc 7
+or
+.Xr man 7
+text from stdin, implying
+.Fl m Ns Cm andoc ,
+and produces
+.Fl T Ns Cm locale
+output.
+.Pp
+The options are as follows:
 .Bl -tag -width Ds
-.It Fl f Ns Ar option...
-Comma-separated compiler options.  See
-.Sx Compiler Options
-for details.
-.
+.It Fl a
+If the standard output is a terminal device and
+.Fl c
+is not specified, use
+.Xr more 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 more 1
+to paginate them.
+This is the default.
+It can be specified to override
+.Fl a .
+.It Fl f
+A synonym for
+.Xr whatis 1 .
+This overrides any earlier
+.Fl k
+and
+.Fl l
+options.
+.Sm off
+.It Fl I Cm os Li = Ar name
+.Sm on
+Override the default operating system
+.Ar name
+for the
+.Xr mdoc 7
+.Sq \&Os
+and for the
+.Xr man 7
+.Sq \&TH
+macro.
+.It Fl h
+Display only the SYNOPSIS lines.
+Implies
+.Fl c .
+.It Fl K Ns 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:
+.Bl -tag -width iso-8859-1
+.It Cm utf-8
+if the first three bytes of the input file
+are the UTF-8 byte order mark (BOM, 0xefbbbf)
+.It Ar encoding
+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 -*-
+.It Cm utf-8
+if the first non-ASCII byte in the file introduces a valid UTF-8 sequence
+.It Cm iso-8859-1
+otherwise
+.El
+.It Fl k
+A synonym for
+.Xr apropos 1 .
+This overrides any earlier
+.Fl f
+and
+.Fl l
+options.
+.It Fl l
+A synonym for
+.Fl a .
+Also reverts any earlier
+.Fl f
+and
+.Fl k
+options.
 .It Fl m Ns Ar format
-Input format.  See
+Input format.
+See
 .Sx Input Formats
-for available formats.  Defaults to
-.Fl m Ns Ar andoc .
-.
-.It Fl O Ns Ar option...
-Comma-separated output options.  See
-.Sx Output Options
-for details.
-.
+for available formats.
+Defaults to
+.Fl m Ns Cm andoc .
+.It Fl O Ns Ar option
+Comma-separated output options.
 .It Fl T Ns Ar output
-Output format.  See
+Output format.
+See
 .Sx Output Formats
-for available formats.  Defaults to
-.Fl T Ns Ar ascii .
-.
+for available formats.
+Defaults to
+.Fl T Ns Cm locale .
 .It Fl V
 Print version and exit.
-.
-.It Fl W Ns Ar err...
-Comma-separated warning options.  Use
-.Fl W Ns Ar all
-to print warnings,
-.Fl W Ns Ar error
-for warnings to be considered errors and cause utility
-termination.  Multiple
-.Fl W
-arguments may be comma-separated, such as
-.Fl W Ns Ar error,all .
-.
-.It Ar infile...
-Read input from zero or more
-.Ar infile .
-If unspecified, reads from stdin.  If multiple files are specified,
+.It Fl W Ns 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 warning ,
+.Cm error ,
+or
+.Cm unsupp ;
+.Cm all
+is an alias for
+.Cm warning .
+By default,
 .Nm
+is silent.
+See
+.Sx EXIT STATUS
+and
+.Sx DIAGNOSTICS
+for details.
+.Pp
+The special option
+.Fl W Ns 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 Ns Cm error , Ns Cm stop .
+.It Ar file
+Read input from zero or more files.
+If unspecified, reads from stdin.
+If multiple files are specified,
+.Nm
 will halt with the first failed parse.
 .El
-.
 .Pp
-By default,
+In
+.Fl f
+and
+.Fl k
+mode,
 .Nm
-reads
-.Xr mdoc 7
-or
-.Xr man 7
-text from stdin, implying
-.Fl m Ns Ar andoc ,
-and produces
-.Fl T Ns Ar ascii
-output.
-.
-.Pp
-.Ex -std mandoc
-.
-.
+also supports the options
+.Fl CMmOSsw
+described in the
+.Xr apropos 1
+manual.
 .Ss Input Formats
 The
 .Nm
@@ -112,20 +215,20 @@ utility accepts
 and
 .Xr man 7
 input with
-.Fl m Ns Ar doc
+.Fl m Ns Cm doc
 and
-.Fl m Ns Ar an ,
-respectively.  The
+.Fl m Ns Cm an ,
+respectively.
+The
 .Xr mdoc 7
 format is
 .Em strongly
 recommended;
 .Xr man 7
 should only be used for legacy manuals.
-.
 .Pp
 A third option,
-.Fl m Ns Ar andoc ,
+.Fl m Ns Cm andoc ,
 which is also the default, determines encoding on-the-fly: if the first
 non-comment macro is
 .Sq \&Dd
@@ -136,392 +239,1506 @@ the
 parser is used; otherwise, the
 .Xr man 7
 parser is used.
-.
 .Pp
 If multiple
 files are specified with
-.Fl m Ns Ar andoc ,
-each has its file-type determined this way.  If multiple files are
+.Fl m Ns Cm andoc ,
+each has its file-type determined this way.
+If multiple files are
 specified and
-.Fl m Ns Ar doc
+.Fl m Ns Cm doc
 or
-.Fl m Ns Ar an
+.Fl m Ns Cm an
 is specified, then this format is used exclusively.
-.
-.
 .Ss Output Formats
 The
 .Nm
 utility accepts the following
 .Fl T
-arguments (see
-.Sx OUTPUT ) :
-.
-.Bl -tag -width Ds
-.It Fl T Ns Ar ascii
-Produce 7-bit ASCII output, backspace-encoded for bold and underline
-styles.  This is the default.  See
+arguments, which correspond to output modes:
+.Bl -tag -width "-Tlocale"
+.It Fl T Ns Cm ascii
+Produce 7-bit ASCII output.
+See
 .Sx ASCII Output .
-.
-.It Fl T Ns Ar html
-Produce strict HTML-4.01 output, with a sane default style.  See
+.It Fl T Ns Cm html
+Produce HTML5, CSS1, and MathML output.
+See
 .Sx HTML Output .
-.
-.It Fl T Ns Ar xhtml
-Produce strict XHTML-1.0 output, with a sane default style.  See
-.Sx XHTML Output .
-.
-.It Fl T Ns Ar tree
-Produce an indented parse tree.
-.
-.It Fl T Ns Ar lint
+.It Fl T Ns Cm lint
 Parse only: produce no output.
+Implies
+.Fl W Ns Cm warning .
+.It Fl T Ns Cm locale
+Encode output using the current locale.
+This is the default.
+See
+.Sx Locale Output .
+.It Fl T Ns Cm man
+Produce
+.Xr man 7
+format output.
+See
+.Sx Man Output .
+.It Fl T Ns Cm pdf
+Produce PDF output.
+See
+.Sx PDF Output .
+.It Fl T Ns Cm ps
+Produce PostScript output.
+See
+.Sx PostScript Output .
+.It Fl T Ns Cm tree
+Produce an indented parse tree.
+.It Fl T Ns Cm utf8
+Encode output in the UTF\-8 multi-byte format.
+See
+.Sx UTF\-8 Output .
+.It Fl T Ns Cm xhtml
+This is a synonym for
+.Fl T Ns Cm html .
 .El
-.
 .Pp
 If multiple input files are specified, these will be processed by the
 corresponding filter in-order.
-.
-.
-.Ss Compiler Options
-Default compiler behaviour may be overridden with the
-.Fl f
-flag.
-.
+.Ss ASCII Output
+Output produced by
+.Fl T Ns Cm ascii
+is rendered in standard 7-bit ASCII documented in
+.Xr ascii 7 .
+.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 .
+.Pp
+The special characters documented in
+.Xr mandoc_char 7
+are rendered best-effort in an ASCII equivalent.
+.Pp
+Output width is limited to 78 visible columns unless literal input lines
+exceed this limit.
+.Pp
+The following
+.Fl O
+arguments are accepted:
 .Bl -tag -width Ds
-.It Fl f Ns Ar ign-scope
-When rewinding the scope of a block macro, forces the compiler to ignore
-scope violations.  This can seriously mangle the resulting tree.
-.Pq mdoc only
-.
-.It Fl f Ns Ar ign-escape
-Ignore invalid escape sequences.
-This is the default, but the option can be used to override an earlier
-.Fl f Ns Ar strict .
-.
-.It Fl f Ns Ar no-ign-escape
-Don't ignore invalid escape sequences.
-.
-.It Fl f Ns Ar no-ign-macro
-Do not ignore unknown macros at the start of input lines.
-.
-.It Fl f Ns Ar no-ign-chars
-Do not ignore disallowed characters.
-.
-.It Fl f Ns Ar strict
-Implies
-.Fl f Ns Ar no-ign-escape ,
-.Fl f Ns Ar no-ign-macro
-and
-.Fl f Ns Ar no-ign-chars .
-.
-.It Fl f Ns Ar ign-errors
-Don't halt when encountering parse errors.  Useful with
-.Fl T Ns Ar lint
-over a large set of manuals passed on the command line.
+.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.
+.It Cm width Ns = Ns Ar width
+The output width is set to
+.Ar width ,
+which will normalise to \(>=58.
 .El
-.
-.
-.Ss Output Options
-For the time being, only
-.Fl T Ns Ar html
-accepts output options:
+.Ss HTML Output
+Output produced by
+.Fl T Ns Cm html
+conforms to HTML5 using optional self-closing tags.
+Default styles use only CSS1.
+Equations rendered from
+.Xr eqn 7
+blocks use MathML.
+.Pp
+The
+.Pa example.style.css
+file documents style-sheet classes available for customising output.
+If a style-sheet is not specified with
+.Fl O Ns Ar style ,
+.Fl T Ns Cm html
+defaults to simple output (via an embedded style-sheet)
+readable in any graphical or text-based web
+browser.
+.Pp
+Special characters are rendered in decimal-encoded UTF\-8.
+.Pp
+The following
+.Fl O
+arguments are accepted:
 .Bl -tag -width Ds
-.It Fl O Ns Ar style=style.css
-The file
-.Ar style.css
-is used for an external style-sheet.  This must be a valid absolute or
-relative URI.
-.It Fl O Ns Ar includes=fmt
+.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
 .Sq \&In
-macro).  Instances of
+macro).
+Instances of
 .Sq \&%I
-are replaced with the include filename.  The default is not to present a
+are replaced with the include filename.
+The default is not to present a
 hyperlink.
-.It Fl O Ns Ar man=fmt
+.It Cm man Ns = 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
 .Sq \&Xr
-macro).  Instances of
+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
+If no section is included, section 1 is assumed.
+The default is not to
 present a hyperlink.
+.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.
 .El
-.
-.
-.Sh OUTPUT
-This section documents output details of
-.Nm .
-In general, output conforms to the traditional manual style of a header,
-a body composed of sections and sub-sections, and a footer.
+.Ss Locale Output
+Locale-depending output encoding is triggered with
+.Fl T Ns Cm locale .
+This is the default.
 .Pp
-The text style of output characters (non-macro characters, punctuation,
-and white-space) is dictated by context.
+This option is not available on all systems: systems without locale
+support, or those whose internal representation is not natively UCS-4,
+will fall back to
+.Fl T Ns Cm ascii .
+See
+.Sx ASCII Output
+for font style specification and available command-line arguments.
+.Ss Man Output
+Translate input format into
+.Xr man 7
+output format.
+This is useful for distributing manual sources to legacy systems
+lacking
+.Xr mdoc 7
+formatters.
 .Pp
-White-space is generally stripped from input.  This can be changed with
-character escapes (specified in
-.Xr mandoc_char 7 )
-or literal modes (specified in
+If
 .Xr mdoc 7
-and
-.Xr man 7 ) .
+is passed as input, it is translated into
+.Xr man 7 .
+If the input format is
+.Xr man 7 ,
+the input is copied to the output, expanding any
+.Xr roff 7
+.Sq so
+requests.
+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 PDF Output
+PDF-1.1 output may be generated by
+.Fl T Ns 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 Ns 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
-If non-macro punctuation is set apart from words, such as in the phrase
-.Dq to be \&, or not to be ,
-it's processed by
-.Nm ,
-regardless of output format, according to the following rules:  opening
-punctuation
-.Po
-.Sq \&( ,
-.Sq \&[ ,
-and
-.Sq \&{
-.Pc
-is not followed by a space; closing punctuation
-.Po
-.Sq \&. ,
-.Sq \&, ,
-.Sq \&; ,
-.Sq \&: ,
-.Sq \&? ,
-.Sq \&! ,
-.Sq \&) ,
-.Sq \&]
-and
-.Sq \&}
-.Pc
-is not preceded by white-space.
-.
+Special characters are rendered as in
+.Sx ASCII Output .
 .Pp
-If the input is
-.Xr mdoc 7 ,
-however, these rules are also applied to macro arguments when appropriate.
-.
-.
-.Ss ASCII Output
-Output produced by
-.Fl T Ns Ar ascii ,
-which is the default, is rendered in standard 7-bit ASCII documented in
-.Xr ascii 7 .
-.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 .
-.Pp
-The special characters documented in
-.Xr mandoc_char 7
-are rendered best-effort in an ASCII equivalent.
-.Pp
-Output width is limited to 78 visible columns unless literal input lines
-exceed this limit.
-.
-.
-.Ss HTML Output
-Output produced by
-.Fl T Ns Ar html
-conforms to HTML-4.01 strict.
-.Pp
-Font styles and page structure are applied using CSS2.  By default, no
-font style is applied to any text, although CSS2 is hard-coded to format
-the basic structure of 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 Ns Cm utf8
+to force a UTF\-8 locale.
+See
+.Sx Locale Output
+for details and options.
+.Sh ENVIRONMENT
+.Bl -tag -width MANPAGER
+.It Ev MANPAGER
+Any non-empty value of the environment variable
+.Ev MANPAGER
+will be used instead of the standard pagination program,
+.Xr more 1 .
+.It Ev PAGER
+Specifies the pagination program to use when
+.Ev MANPAGER
+is not defined.
+If neither PAGER nor MANPAGER is defined,
+.Pa /usr/bin/more Fl s
+will be used.
+.El
+.Sh EXIT STATUS
 The
-.Pa example.style.css
-file documents the range of styles applied to output and, if used, will
-cause rendered documents to appear as they do in
-.Fl T Ns Ar ascii .
+.Nm
+utility exits with one of the following values, controlled by the message
+.Ar level
+associated with the
+.Fl W
+option:
 .Pp
-Special characters are rendered in decimal-encoded UTF-8.
-.
-.
-.Ss XHTML Output
-Output produced by
-.Fl T Ns Ar xhtml
-conforms to XHTML-1.0 strict.
+.Bl -tag -width Ds -compact
+.It 0
+No warnings or errors occurred, or those that did were ignored because
+they were lower than the requested
+.Ar level .
+.It 2
+At least one warning occurred, but no error, and
+.Fl W Ns Cm warning
+was specified.
+.It 3
+At least one parsing error occurred,
+but no unsupported feature was encountered, and
+.Fl W Ns Cm error
+or
+.Fl W Ns Cm warning
+was specified.
+.It 4
+At least one unsupported feature was encountered, and
+.Fl W Ns Cm unsupp ,
+.Fl W Ns Cm error
+or
+.Fl W Ns Cm warning
+was specified.
+.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 cause
+.Nm
+to exit at once, possibly in the middle of parsing or formatting a file.
+.El
 .Pp
-See
-.Sx HTML Output
-for details; beyond generating XHTML tags instead of HTML tags, these
-output modes are identical.
-.
-.
+Note that selecting
+.Fl T Ns Cm lint
+output mode implies
+.Fl W Ns Cm warning .
 .Sh EXAMPLES
 To page manuals to the terminal:
-.
 .Pp
-.D1 % mandoc \-Wall,error \-fstrict mandoc.1 2>&1 | less
-.D1 % mandoc mandoc.1 mdoc.3 mdoc.7 | less
-.
+.Dl $ mandoc \-Wall,stop mandoc.1 2\*(Gt&1 | less
+.Dl $ mandoc mandoc.1 mdoc.3 mdoc.7 | less
 .Pp
 To produce HTML manuals with
 .Ar style.css
 as the style-sheet:
 .Pp
-.D1 % mandoc \-Thtml -Ostyle=style.css mdoc.7 > mdoc.7.html
+.Dl $ mandoc \-Thtml -Ostyle=style.css mdoc.7 \*(Gt mdoc.7.html
 .Pp
 To check over a large set of manuals:
-.
 .Pp
-.Dl % mandoc \-Tlint \-fign-errors `find /usr/src -name \e*\e.[1-9]`
-.
-.
-.Sh COMPATIBILITY
-This section summarises
+.Dl $ mandoc \-Tlint `find /usr/src -name \e*\e.[1-9]`
+.Pp
+To produce a series of PostScript manuals for A4 paper:
+.Pp
+.Dl $ mandoc \-Tps \-Opaper=a4 mdoc.7 man.7 \*(Gt 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 \-Tman foo.mdoc \*(Gt foo.man
+.Sh DIAGNOSTICS
+Messages displayed by
 .Nm
-compatibility with
-.Xr groff 1 .
-Each input and output format is separately noted.
-.
-.
-.Ss ASCII Compatibility
-.Bl -bullet -compact
-.It
+follow this format:
+.Pp
+.D1 Nm Ns : Ar file : Ns Ar line : Ns Ar column : level : message : macro args
+.Pp
+Line and column numbers start at 1.
+Both are omitted for messages referring to an input file as a whole.
+Macro names and arguments are omitted where meaningless.
+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 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
+An input file contains invalid syntax that cannot be safely interpreted.
+By discarding part of the input or inserting missing tokens,
+the parser is able to continue, and the error does not prevent
+generation of formatted output, but typically, preparing that
+output involves information loss, broken document structure
+or unintended formatting, no matter whether
+.Nm
+or GNU troff is used.
+In many cases, the output of
+.Nm
+and GNU troff is identical, but in some,
+.Nm
+is more resilient than GNU troff with respect to malformed input.
+.Pp
+Non-existent or unreadable input files are also reported on the
+.Cm error
+level.
+In that case, the parser cannot even be started and no output
+is produced from those input files.
+.It Cm warning
+An input file uses obsolete, discouraged or non-portable syntax.
+All the same, the meaning of the input is unambiguous and a correct
+rendering can be produced.
+Documents causing warnings may render poorly when using other
+formatting tools instead of
+.Nm .
+.El
+.Pp
+Messages of the
+.Cm warning ,
+.Cm error ,
+and
+.Cm unsupp
+levels except those about non-existent or unreadable input files
+are hidden unless their level, or a lower level, is requested using a
+.Fl W
+option or
+.Fl T Ns Cm lint
+output mode.
+.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 "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 "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 "missing date, using today's date"
+.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 "missing Os macro, using \(dq\(dq"
+.Pq mdoc
+The default or current system is not shown in this case.
+.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 "late prologue macro"
+.Pq mdoc
+A
+.Ic \&Dd
+or
+.Ic \&Os
+macro occurs after some non-prologue macro, but still takes effect.
+.It Sy "skipping late title macro"
+.Pq mdoc
 The
-.Sq \e~
-special character doesn't produce expected behaviour in
-.Fl T Ns Ar ascii .
-.
-.It
-The
-.Sq \&Bd \-literal
+.Ic \&Dt
+macro can only occur before the first non-prologue macro
+because traditional formatters 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 "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
-.Sq \&Bd \-unfilled
-macros of
+.Xr apropos 1 .
+.It Sy "bad NAME section contents"
+.Pq mdoc
+The last node in the NAME section is not an
+.Ic \&Nd
+macro, or any preceding macro is not
+.Ic \&Nm ,
+or the NAME section is completely empty.
+This may confuse
+.Xr makewhatis 8
+and
+.Xr apropos 1 .
+.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 "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 "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 refering 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
-in
-.Fl T Ns Ar ascii
-are synonyms, as are \-filled and \-ragged.
-.
-.It
+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 line;
+otherwise, escape it by prepending
+.Sq \e& .
+.It Sy "skipping paragraph macro"
 In
-.Xr groff 1 ,
-the
-.Sq \&Pa
 .Xr mdoc 7
-macro does not underline when scoped under an
-.Sq \&It
-in the FILES section.  This behaves correctly in
-.Nm .
-.
+documents, this happens
+.Bl -dash -compact
 .It
-A list or display following
-.Sq \&Ss
-.Xr mdoc 7
-macro in
-.Fl T Ns Ar ascii
-does not assert a prior vertical break, just as it doesn't with
-.Sq \&Sh .
-.
+at the beginning and end of sections and subsections
 .It
-The
-.Sq \&na
+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
-macro in
-.Fl T Ns Ar ascii
-has no effect.
-.
+documents, it happens
+.Bl -dash -compact
 .It
-Words aren't hyphenated.
-.
+for empty
+.Ic \&P ,
+.Ic \&PP ,
+and
+.Ic \&LP
+macros
 .It
-In normal mode (not a literal block), blocks of spaces aren't preserved,
-so double spaces following sentence closure are reduced to a single space;
-.Xr groff 1
-retains spaces.
-.
+for
+.Ic \&IP
+macros having neither head nor body arguments
 .It
-Sentences are unilaterally monospaced.
+for
+.Ic \&br
+or
+.Ic \&sp
+right after
+.Ic \&SH
+or
+.Ic \&SS
 .El
-.
-.
-.Ss HTML/XHTML Compatibility
-.Bl -bullet -compact
+.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.
+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 ".Vt block has child macro"
+.Pq mdoc
+The
+.Ic \&Vt
+macro supports plain text arguments only.
+Formatting may be ugly and semantic searching
+for the affected content might not work.
+.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 "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 \efP
-escape will revert the font to the previous
-.Sq \ef
-escape, not to the last rendered decoration, which is now dictated by
-CSS instead of hard-coded.  It also will not span past the current
-scope, for the same reason.  Note that in
-.Sx ASCII Output
-mode, this will work fine.
+.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 \&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
-.Sq \&Bl \-hang
+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 font type"
+.Pq mdoc
+A
+.Ic \&Bf
+macro has no argument.
+It switches to the default font,
+.Cm \efR .
+.It Sy "unknown font type"
+.Pq mdoc
+The
+.Ic \&Bf
+argument is invalid.
+The default font
+.Cm \efR
+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 -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 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 "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 "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 "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 "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 "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.
+.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 replaced with
+.Ic \&sp
+requests.
+.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 "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.
+.It Sy "invalid escape sequence"
+.Pq roff
+An escape sequence has an invalid opening argument delimiter, lacks the
+closing argument delimiter, or the argument has too few characters.
+If the argument is incomplete,
+.Ic \e*
 and
-.Sq \&Bl \-tag
-list types render similarly (no break following overreached left-hand
-side) due to the expressive constraints of HTML.
-.
+.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 invalid escape sequences are ignored.
+.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 "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 "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 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 \&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 "scope open on exit"
+.Pq mdoc , man , eqn , tbl , roff
+At the end of the document, an explicit
+.Xr mdoc 7
+block, a
 .Xr man 7
-.Sq IP
+next-line scope or
+.Ic \&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
-.Sq TP
-lists render similarly.
+.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 "argument count wrong"
+.Pq mdoc , man , roff
+The indicated request or macro has too few or too many arguments.
+The syntax tree will contain the wrong number of arguments as given.
+Formatting behaviour depends on the specific request or macro in question.
+Note that the same message may also occur as a WARNING, see above.
+.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 "missing list type, using -item"
+.Pq mdoc
+A
+.Ic \&Bl
+macro fails to specify the list type.
+.It Sy "missing manual name, using \(dq\(dq"
+.Pq mdoc
+The first call to
+.Ic \&Nm
+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 "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
+The
+.Ic \&An
+macro is invoked with another argument after
+.Fl split
+or
+.Fl nosplit ,
+.Ic \&Fo
+is invoked with more than one argument,
+.Ic \&Bd ,
+.Ic \&Bk ,
+or
+.Ic \&Bl
+are invoked with invalid arguments, the
+.Ic \&RE
+macro is invoked with more than one argument
+or with a non-integer argument, the
+.Ic \&PD
+macro or the
+.Ic \&ft
+or
+.Ic \&sp
+request is invoked with more than one argument, or a request of the
+.Ic \&de
+family is invoked with more than two arguments.
+The excess arguments are ignored.
 .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 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.
+.El
 .Sh SEE ALSO
+.Xr apropos 1 ,
+.Xr man 1 ,
+.Xr eqn 7 ,
+.Xr man 7 ,
 .Xr mandoc_char 7 ,
 .Xr mdoc 7 ,
-.Xr man 7
-.
+.Xr roff 7 ,
+.Xr tbl 7
 .Sh AUTHORS
 The
 .Nm
 utility was written by
-.An Kristaps Dzonsons Aq kristaps@kth.se .
-.
-.
-.Sh CAVEATS
-The
-.Fl T Ns Ar html
-and
-.Fl T Ns Ar xhtml
-CSS2 styling used for
-.Fl m Ns Ar doc
-input lists does not render properly in brain-dead browsers, such as
-Internet Explorer 6 and earlier.
-.Pp
+.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
+and is maintained by
+.An Ingo Schwarze Aq Mt schwarze@openbsd.org .
+.Sh BUGS
 In
-.Fl T Ns Ar html
-and
-.Fl T Ns Ar xhtml ,
+.Fl T Ns Cm html ,
 the maximum size of an element attribute is determined by
 .Dv BUFSIZ ,
-which is usually 1024 bytes.  Be aware of this when setting long link
-formats, e.g.,
-.Fl O Ns Ar style=really/long/link .
-.Pp
-The
-.Fl T Ns Ar html
-and
-.Fl T Ns Ar xhtml
-output modes don't render the
-.Sq \es
-font size escape documented in
-.Xr mdoc 7
-and
-.Xr man 7 .
+which is usually 1024 bytes.
+Be aware of this when setting long link
+formats such as
+.Fl O Ns Cm style Ns = Ns Ar really/long/link .