Document DateTime.posix(:real)

doc/Type/DateTime.rakudoc

@@ -300,8 +300,17 @@ Returns the date and time as a POSIX/UNIX timestamp (integral seconds since the
 If C<$ignore-timezone> is C<True>, the C<DateTime> object will be treated as if
 the time zone offset is zero.
 
+    method posix(Bool:D: $ignore-timezone = False, :real --> Num:D)
+
+As of release 2022.06 of the Rakudo compiler, it is also possible to specify a
+C<:real> named argument.  If specified with a true value, a C<Num> will be
+returned, allowing for sub-second accuracy of the number of seconds since the
+POSIX epoch.
+
 =for code
-say DateTime.new('2015-12-24T12:23:00Z').posix;       # OUTPUT: «1450959780␤»
+say DateTime.new('2015-12-24T12:23:00Z').posix;           # OUTPUT: «1450959780␤»
+say DateTime.new('2022-06-21T12:23:00.5Z').posix;         # OUTPUT: «1655814180␤»
+say DateTime.new('2022-06-21T12:23:00.5Z').posix(:real);  # OUTPUT: «1655814180.5␤»
 
 =head2 method truncated-to