+.Dl $ mandoc \-T lint \(gafind /usr/src -name \e*\e.[1-9]\(ga
+.Pp
+To produce a series of PostScript manuals for A4 paper:
+.Pp
+.Dl $ mandoc \-T ps \-O paper=a4 mdoc.7 man.7 > manuals.ps
+.Pp
+Convert a modern
+.Xr mdoc 7
+manual to the older
+.Xr man 7
+format, for use on systems lacking an
+.Xr mdoc 7
+parser:
+.Pp
+.Dl $ mandoc \-T man foo.mdoc > foo.man
+.Sh DIAGNOSTICS
+Messages displayed by
+.Nm
+follow this format:
+.Bd -ragged -offset indent
+.Nm :
+.Ar file : Ns Ar line : Ns Ar column : level : message : macro arguments
+.Pq Ar os
+.Ed
+.Pp
+The first three fields identify the
+.Ar file
+name,
+.Ar line
+number, and
+.Ar column
+number of the input file where the message was triggered.
+The line and column numbers start at 1.
+Both are omitted for messages referring to an input file as a whole.
+All
+.Ar level
+and
+.Ar message
+strings are explained below.
+The name of the
+.Ar macro
+triggering the message and its
+.Ar arguments
+are omitted where meaningless.
+The
+.Ar os
+operating system specifier is omitted for messages that are relevant
+for all operating systems.
+Fatal messages about invalid command line arguments
+or operating system errors, for example when memory is exhausted,
+may also omit the
+.Ar file
+and
+.Ar level
+fields.
+.Pp
+Message levels have the following meanings:
+.Bl -tag -width "warning"
+.It Cm syserr
+An operating system error occurred.
+There isn't necessarily anything wrong with the input files.
+Output may all the same be missing or incomplete.
+.It Cm badarg
+Invalid command line arguments were specified.
+No input files have been read and no output is produced.
+.It Cm unsupp
+An input file uses unsupported low-level
+.Xr roff 7
+features.
+The output may be incomplete and/or misformatted,
+so using GNU troff instead of
+.Nm
+to process the file may be preferable.
+.It Cm error
+Indicates a risk of information loss or severe misformatting,
+in most cases caused by serious syntax errors.
+.It Cm warning
+Indicates a risk that the information shown or its formatting
+may mismatch the author's intent in minor ways.
+Additionally, syntax errors are classified at least as warnings,
+even if they do not usually cause misformatting.
+.It Cm style
+An input file uses dubious or discouraged style.
+This is not a complaint about the syntax, and probably neither
+formatting nor portability are in danger.
+While great care is taken to avoid false positives on the higher
+message levels, the
+.Cm style
+level tries to reduce the probability that issues go unnoticed,
+so it may occasionally issue bogus suggestions.
+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 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