+The \es (font size), \em (font colour), and \eM (font filling colour)
+font decoration escapes are all discarded in mandoc.
+.It
+Old groff fails to assert a newline before
+.Sx \&Bd Fl ragged compact .
+.It
+groff behaves inconsistently when encountering
+.Pf non- Sx \&Fa
+children of
+.Sx \&Fo
+regarding spacing between arguments.
+In mandoc, this is not the case: each argument is consistently followed
+by a single space and the trailing
+.Sq \&)
+suppresses prior spacing.
+.It
+groff behaves inconsistently when encountering
+.Sx \&Ft
+and
+.Sx \&Fn
+in the
+.Em SYNOPSIS :
+at times newline(s) are suppressed depending on whether a prior
+.Sx \&Fn
+has been invoked.
+In mandoc, this is not the case.
+See
+.Sx \&Ft
+and
+.Sx \&Fn
+for the normalised behaviour.
+.It
+Historic groff does not break before an
+.Sx \&Fn
+when not invoked as the line macro in the
+.Em SYNOPSIS
+section.
+.It
+Historic groff formats the
+.Sx \&In
+badly: trailing arguments are trashed and
+.Em SYNOPSIS
+is not specially treated.
+.It
+groff does not accept the
+.Sq \&Ta
+pseudo-macro as a line macro.
+mandoc does.
+.It