+A one-line description of the manual's content.
+This may only be invoked in the
+.Em SYNOPSIS
+section subsequent the
+.Sx \&Nm
+macro.
+.Pp
+Examples:
+.D1 \&.Sx \&Nd mdoc language reference
+.D1 \&.Sx \&Nd format and display UNIX manuals
+.Pp
+The
+.Sx \&Nd
+macro technically accepts child macros and terminates with a subsequent
+.Sx \&Sh
+invocation.
+Do not assume this behaviour: some
+.Xr whatis 1
+database generators are not smart enough to parse more than the line
+arguments and will display macros verbatim.
+.Pp
+See also
+.Sx \&Nm .