+.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 Compiler Options
+Default
+.Xr mdoc 7
+and
+.Xr man 7
+compilation behaviour may be overridden with the
+.Fl f
+flag.
+.Bl -tag -width Ds
+.It Fl f Ns Cm ign-errors
+When parsing multiple files, don't halt when one errors out.
+Useful with
+.Fl T Ns Cm lint
+over a large set of manuals passed on the command line.
+.It Fl f Ns Cm ign-escape
+Ignore invalid escape sequences.
+This is the default, but the option can be used to override an earlier
+.Fl f Ns Cm strict .
+.It Fl f Ns Cm 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 Cm no-ign-escape
+Do not ignore invalid escape sequences.
+.It Fl f Ns Cm no-ign-macro
+Do not ignore unknown macros at the start of input lines.
+.It Fl f Ns Cm strict
+Implies
+.Fl f Ns Cm no-ign-escape
+and
+.Fl f Ns Cm no-ign-macro .
+.El