+.
+.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
+.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
+.Nm
+compatibility with
+.Xr groff 1 .
+Each input and output format is separately noted.
+.
+.
+.Ss ASCII output
+.Bl -bullet -compact
+.It
+The
+.Sq \e~
+special character doesn't produce expected behaviour in
+.Fl T Ns Ar ascii .
+.
+.It
+The
+.Sq \&Bd \-literal
+and
+.Sq \&Bd \-unfilled
+macros of
+.Xr mdoc 7
+in
+.Fl T Ns Ar ascii
+are synonyms, as are \-filled and \-ragged.
+.
+.It
+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 .
+.
+.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 .
+.
+.It
+The
+.Sq \&na
+.Xr man 7
+macro in
+.Fl T Ns Ar ascii
+has no effect.
+.
+.It
+Words aren't hyphenated.
+.
+.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.
+.
+.It
+Sentences are unilaterally monospaced.
+.El