+.Sx \&At
+with unknown arguments produces no output at all.
+\*[hist]
+Newer groff and mandoc print
+.Qq AT&T UNIX
+and the arguments.
+.It
+.Sx \&Bd Fl column
+does not recognize trailing punctuation characters when they immediately
+precede tabulator characters, but treats them as normal text and
+outputs a space before them.
+.It
+.Sx \&Bd Fl ragged compact
+does not start a new line.
+\*[hist]
+.It
+.Sx \&Dd
+without an argument prints