Document extra magic of $() 6.c shortcut

It doesn't just stringify, but actually checks .ast value first
and returns it if it's truthy or stringifies match object if not.

doc/Language/variables.pod6

@@ -1032,15 +1032,15 @@ say $/;
 #             textnode => ｢some text｣␤»
 =end code
 
-To get a stringified version of the L<Match> object, simply use the
-L<prefix ~ operator|https://docs.perl6.org/routine/~.html#(Operators)_prefix_~>.
-In 6.c language, you can use C<$()> shortcut (no spaces inside the parentheses).
+In 6.c language, you can use C<$()> shortcut (no spaces inside the parentheses) to get
+the L<ast> value from C<$/> L<Match> if that value is truthy, or the stringification of the
+L<Match> object otherwise.
 
     'test' ~~ /.../;
-    say ~$/; # OUTPUT: «tes␤»
-
     # 6.c language only:
     say $(); # OUTPUT: «tes␤»;
+    $/.make: 'McTesty';
+    say $(); # OUTPUT: «McTesty␤»;
 
 =head4 X«Positional attributes|variable,$0;variable,$1;variable,@()»