===================================================================
RCS file: /cvs/mandoc/mandoc.1,v
retrieving revision 1.175
retrieving revision 1.244
diff -u -p -r1.175 -r1.244
--- mandoc/mandoc.1	2017/03/03 14:23:23	1.175
+++ mandoc/mandoc.1	2020/06/15 18:05:18	1.244
@@ -1,7 +1,7 @@
-.\"	$Id: mandoc.1,v 1.175 2017/03/03 14:23:23 schwarze Exp $
+.\" $OpenBSD: mandoc.1,v 1.244 2020/06/15 18:05:18 schwarze Exp $
 .\"
+.\" Copyright (c) 2012, 2014-2020 Ingo Schwarze <schwarze@openbsd.org>
 .\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
-.\" Copyright (c) 2012, 2014-2017 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
@@ -15,28 +15,26 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: March 3 2017 $
+.Dd $Mdocdate: June 15 2020 $
 .Dt MANDOC 1
 .Os
 .Sh NAME
 .Nm mandoc
-.Nd format and display UNIX manuals
+.Nd format manual pages
 .Sh SYNOPSIS
 .Nm mandoc
-.Op Fl acfhkl
+.Op Fl ac
 .Op Fl I Cm os Ns = Ns Ar name
 .Op Fl K Ar encoding
-.Op Fl m Ns Ar format
-.Op Fl O Ar option
+.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
-.Ux
-manual pages for display.
+utility formats manual pages for display.
 .Pp
 By default,
 .Nm
@@ -44,9 +42,7 @@ reads
 .Xr mdoc 7
 or
 .Xr man 7
-text from stdin, implying
-.Fl m Ns Cm andoc ,
-and produces
+text from stdin and produces
 .Fl T Cm locale
 output.
 .Pp
@@ -67,27 +63,15 @@ 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.
-.It Fl h
-Display only the SYNOPSIS lines.
-Implies
-.Fl c .
 .It Fl I Cm os Ns = Ns Ar name
 Override the default operating system
 .Ar name
 for the
 .Xr mdoc 7
-.Sq \&Os
+.Ic \&Os
 and for the
 .Xr man 7
-.Sq \&TH
+.Ic \&TH
 macro.
 .It Fl K Ar encoding
 Specify the input encoding.
@@ -98,54 +82,80 @@ arguments are
 .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
+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 -*-
-.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
+.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 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
-.Sx Input Formats
-for available formats.
-Defaults to
-.Fl m Ns Cm andoc .
-.It Fl O Ar option
+.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
-Output format.
-See
-.Sx Output Formats
-for available formats.
-Defaults to
-.Fl T Cm locale .
+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
@@ -153,13 +163,33 @@ to be reported on the standard error output and to aff
 The
 .Ar level
 can be
+.Cm base ,
+.Cm style ,
 .Cm warning ,
 .Cm error ,
 or
-.Cm unsupp ;
+.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 warning .
+.Cm base .
 By default,
 .Nm
 is silent.
@@ -183,13 +213,17 @@ and
 are requested, they can be joined with a comma, for example
 .Fl W 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,
+Read from the given input file.
+If multiple files are specified, they are processed in the given order.
+If unspecified,
 .Nm
-will halt with the first failed parse.
+reads from standard input.
 .El
 .Pp
+The options
+.Fl fhklw
+are also supported and are documented in
+.Xr man 1 .
 In
 .Fl f
 and
@@ -197,117 +231,21 @@ and
 mode,
 .Nm
 also supports the options
-.Fl CMmOSsw
+.Fl CMmOSs
 described in the
 .Xr apropos 1
 manual.
-.Ss Input Formats
-The
-.Nm
-utility accepts
-.Xr mdoc 7
-and
-.Xr man 7
-input with
-.Fl m Ns Cm doc
-and
-.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 Cm andoc ,
-which is also the default, determines encoding on-the-fly: if the first
-non-comment macro is
-.Sq \&Dd
-or
-.Sq \&Dt ,
-the
-.Xr mdoc 7
-parser is used; otherwise, the
-.Xr man 7
-parser is used.
-.Pp
-If multiple
-files are specified with
-.Fl m Ns Cm andoc ,
-each has its file-type determined this way.
-If multiple files are
-specified and
-.Fl m Ns Cm doc
-or
-.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, which correspond to output modes:
-.Bl -tag -width "-T markdown"
-.It Fl T Cm ascii
-Produce 7-bit ASCII output.
-See
-.Sx ASCII Output .
-.It Fl T Cm html
-Produce HTML5, CSS1, and MathML output.
-See
-.Sx HTML Output .
-.It Fl T Cm lint
-Parse only: produce no output.
-Implies
-.Fl W Cm warning .
-.It Fl T Cm locale
-Encode output using the current locale.
-This is the default.
-See
-.Sx Locale Output .
-.It Fl T Cm man
-Produce
-.Xr man 7
-format output.
-See
-.Sx Man Output .
-.It Fl T Cm markdown
-Produce output in
-.Sy markdown
-format.
-See
-.Sx Markdown Output .
-.It Fl T Cm pdf
-Produce PDF output.
-See
-.Sx PDF Output .
-.It Fl T Cm ps
-Produce PostScript output.
-See
-.Sx PostScript Output .
-.It Fl T Cm tree
-Produce an indented parse tree.
-See
-.Sx Syntax tree output .
-.It Fl T Cm utf8
-Encode output in the UTF\-8 multi-byte format.
-See
-.Sx UTF\-8 Output .
-.It Fl T Cm xhtml
-This is a synonym for
-.Fl T Cm html .
-.El
-.Pp
-If multiple input files are specified, these will be processed by the
-corresponding filter in-order.
+The options
+.Fl fkl
+are mutually exclusive and override each other.
 .Ss ASCII Output
-Output produced by
+Use
 .Fl T Cm ascii
-is rendered in standard 7-bit ASCII documented in
-.Xr ascii 7 .
+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
@@ -319,14 +257,29 @@ where
 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
-Output width is limited to 78 visible columns unless literal input lines
-exceed this limit.
-.Pp
 The following
 .Fl O
 arguments are accepted:
@@ -340,10 +293,50 @@ 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.
+Specifically, this suppresses the two additional blank lines near the
+top and the bottom of each page, 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 ,
-which will normalise to \(>=58.
+.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
@@ -354,9 +347,9 @@ Equations rendered from
 .Xr eqn 7
 blocks use MathML.
 .Pp
-The
-.Pa mandoc.css
-file documents style-sheet classes available for customising output.
+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
@@ -364,7 +357,8 @@ 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.
+Non-ASCII characters are rendered
+as hexadecimal Unicode character references.
 .Pp
 The following
 .Fl O
@@ -383,20 +377,20 @@ The string
 for example,
 .Ar ../src/%I.html ,
 is used as a template for linked header files (usually via the
-.Sq \&In
+.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
+.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
-.Sq \&Xr
+.Ic \&Xr
 macro).
 Instances of
 .Sq \&%N
@@ -406,43 +400,77 @@ are replaced with the linked manual's name and section
 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
+This argument does not work with
+.Xr more 1
+or
+.Xr less 1 .
+.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
-Locale-depending output encoding is triggered with
+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 .
-This is the default.
-.Pp
-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 Cm ascii .
-See
-.Sx ASCII Output
-for font style specification and available command-line arguments.
 .Ss Man Output
-Translate input format into
+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
-.Xr mdoc 7
-is passed as input, it is translated into
-.Xr man 7 .
-If the input format is
+If the input format of a file is
 .Xr man 7 ,
 the input is copied to the output, expanding any
 .Xr roff 7
-.Sq so
+.Ic so
 requests.
 The parser is also run, and as usual, the
 .Fl W
@@ -450,14 +478,24 @@ level controls which
 .Sx DIAGNOSTICS
 are displayed before copying the input to the output.
 .Ss Markdown Output
-Translate
+Use
+.Fl T Cm markdown
+to translate
 .Xr mdoc 7
-input to the
-.Sy markdown
-format conforming to
+input to the markdown format conforming to
 .Lk http://daringfireball.net/projects/markdown/syntax.text\
  "John Gruber's 2004 specification" .
+The output also almost conforms to the
+.Lk http://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;
@@ -515,13 +553,24 @@ If an unknown value is encountered,
 .Ar letter
 is used.
 .El
-.Ss UTF\-8 Output
+.Ss UTF-8 Output
 Use
 .Fl T Cm utf8
-to force a UTF\-8 locale.
+to force text output in UTF-8 multi-byte character encoding,
+ignoring the
+.Xr locale 1
+settings in the environment.
 See
-.Sx Locale Output
-for details and options.
+.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
@@ -590,11 +639,26 @@ 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
-will be used instead of the standard pagination program,
-.Xr more 1 .
+is used instead of the standard pagination program,
+.Xr more 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
@@ -602,7 +666,12 @@ is not defined.
 If neither PAGER nor MANPAGER is defined,
 .Xr more 1
 .Fl s
-will be used.
+is used.
+Only used if
+.Fl a
+or
+.Fl l
+is specified.
 .El
 .Sh EXIT STATUS
 The
@@ -615,34 +684,43 @@ option:
 .Pp
 .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
+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
-was specified.
+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
-.Fl W Cm warning
-was specified.
+or a lower
+.Ar level
+was requested.
 .It 4
 At least one unsupported feature was encountered, and
-.Fl W Cm unsupp ,
-.Fl W Cm error
-or
-.Fl W Cm warning
-was specified.
+.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 cause
+Such errors may cause
 .Nm
 to exit at once, possibly in the middle of parsing or formatting a file.
 .El
@@ -650,18 +728,17 @@ to exit at once, possibly in the middle of parsing or 
 Note that selecting
 .Fl T Cm lint
 output mode implies
-.Fl W Cm warning .
+.Fl W Cm all .
 .Sh EXAMPLES
 To page manuals to the terminal:
 .Pp
-.Dl $ mandoc \-W all,stop mandoc.1 2\*(Gt&1 | less
-.Dl $ mandoc mandoc.1 mdoc.3 mdoc.7 | less
+.Dl $ mandoc -l mandoc.1 man.1 apropos.1 makewhatis.8
 .Pp
 To produce HTML manuals with
-.Pa mandoc.css
+.Pa /usr/share/misc/mandoc.css
 as the style-sheet:
 .Pp
-.Dl $ mandoc \-T html -O style=mandoc.css mdoc.7 \*(Gt mdoc.7.html
+.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
@@ -669,7 +746,7 @@ To check over a large set of manuals:
 .Pp
 To produce a series of PostScript manuals for A4 paper:
 .Pp
-.Dl $ mandoc \-T ps \-O paper=a4 mdoc.7 man.7 \*(Gt manuals.ps
+.Dl $ mandoc \-T ps \-O paper=a4 mdoc.7 man.7 > manuals.ps
 .Pp
 Convert a modern
 .Xr mdoc 7
@@ -679,17 +756,40 @@ format, for use on systems lacking an
 .Xr mdoc 7
 parser:
 .Pp
-.Dl $ mandoc \-T man foo.mdoc \*(Gt foo.man
+.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
-.D1 Nm Ns : Ar file : Ns Ar line : Ns Ar column : level : message : macro args
-.Pp
-Line and column numbers start at 1.
+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.
-Macro names and arguments are omitted where meaningless.
+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
@@ -700,6 +800,13 @@ 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
@@ -709,45 +816,259 @@ 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.
+Indicates a risk of information loss or severe misformatting,
+in most cases caused by serious syntax errors.
 .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 .
+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.
+Please use your good 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 except those about non-existent or unreadable input files
-are hidden unless their level, or a lower level, is requested using a
+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.
+.It Sy "referenced manual not found"
+.Pq mdoc
+An
+.Ic \&Xr
+macro references a manual page that is not found in the base system.
+The path to look for base system manuals is configurable at compile
+time and defaults to
+.Pa /usr/share/man : /usr/X11R6/man .
+.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 "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 "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"
@@ -762,13 +1083,6 @@ macro before the first non-prologue macro.
 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
@@ -781,7 +1095,21 @@ macro lacks the mandatory section argument.
 The section number in a
 .Ic \&Dt
 line is invalid, but still used.
-.It Sy "missing date, using today's date"
+.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
@@ -804,13 +1132,17 @@ The date given in a
 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 "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
@@ -818,17 +1150,6 @@ A
 or
 .Ic \&Os
 macro occurs after some non-prologue macro, but still takes effect.
-.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 "prologue macros out of order"
 .Pq mdoc
 The prologue macros are not given in the conventional order
@@ -900,6 +1221,14 @@ 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.
@@ -912,6 +1241,24 @@ The same standard section title occurs more than once.
 .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
@@ -998,7 +1345,9 @@ The paragraph macro is moved after the end of the list
 .Pq mdoc
 An input line begins with an
 .Ic \&Ns
-macro.
+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
@@ -1039,20 +1388,12 @@ 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 "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 "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,
@@ -1106,6 +1447,7 @@ A
 .Ic \&Bl ,
 .Ic \&D1 ,
 .Ic \&Dl ,
+.Ic \&MT ,
 .Ic \&RS ,
 or
 .Ic \&UR
@@ -1118,7 +1460,7 @@ or
 .Ic \&Bl
 .Fl offset
 or
-.Fl width.
+.Fl width .
 .It Sy "missing display type, using -ragged"
 .Pq mdoc
 The
@@ -1183,6 +1525,17 @@ 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
@@ -1241,6 +1594,8 @@ 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.
@@ -1252,14 +1607,6 @@ 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
@@ -1340,6 +1687,12 @@ 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
@@ -1357,6 +1710,12 @@ 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
@@ -1383,9 +1742,12 @@ The meaning of blank input lines is only well-defined 
 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
+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:
@@ -1395,26 +1757,15 @@ As an implementation dependent choice, tab characters 
 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 "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 "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.
+closing argument delimiter, the argument is of an invalid form, or it is
+a character escape sequence with an invalid name.
 If the argument is incomplete,
 .Ic \e*
 and
@@ -1427,6 +1778,12 @@ and
 .Ic \ew
 to the length of the incomplete argument.
 All other 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,
@@ -1517,6 +1874,21 @@ 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,
@@ -1555,6 +1927,13 @@ or
 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
@@ -1587,7 +1966,7 @@ An
 .Xr mdoc 7
 block closing macro, a
 .Xr man 7
-.Ic \&RE
+.Ic \&ME , \&RE
 or
 .Ic \&UE
 macro, an
@@ -1621,7 +2000,7 @@ At the end of the document, an explicit
 block, a
 .Xr man 7
 next-line scope or
-.Ic \&RS
+.Ic \&MT , \&RS
 or
 .Ic \&UR
 block, an equation, table, or
@@ -1664,6 +2043,14 @@ When parsing for a request or a user-defined macro nam
 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 "NOT IMPLEMENTED: Bd -file"
 .Pq mdoc
 For security reasons, the
@@ -1687,6 +2074,18 @@ whatever mode was active before the block.
 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 "missing manual name, using \(dq\(dq"
 .Pq mdoc
 The first call to
@@ -1721,6 +2120,13 @@ 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,
@@ -1788,6 +2194,7 @@ 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 ,
@@ -1842,6 +2249,13 @@ 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
@@ -1869,6 +2283,43 @@ or
 macro or of an undefined macro.
 The macro is ignored, and its arguments are handled
 as if they were a text line.
+.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.
 .El
 .Sh SEE ALSO
 .Xr apropos 1 ,