Expanding and adding examples to circumfix []

Which would close #2360 if everyone is happy with it. It's the best
one can do meanwhile the contexts are not better explained, as
requested in #1225.

doc/Language/operators.pod6

@@ -509,7 +509,19 @@ To always ensure you end up with a L<Hash>, you can use C<%( )> coercer or L<has
 =head2 circumfix C«[ ]»
 
 The X<L<Array> constructor> returns an itemized L<Array> that does not flatten
-in list context.
+in list context. Check this:
+
+    say .perl for [3,2,[1,0]; # OUTPUT: «3␤2␤$[1, 0]␤»
+
+This array is itemized, in the sense that every element constitutes an item, as
+shown by the C<$> preceding the last element of the array, the
+L<(list) item contextualizer|https://docs.perl6.org/type/Any#index-entry-%24_%28item_contextualizer%29>.
+
+The output will be (almost) the same if we attempt to flatten it using
+L<C<|> a. k. a. I<the flattener>|/routine/|>, which puts it in a list context:
+
+say .perl for | 3,2,[1,0]; # OUTPUT: «3␤2␤[1, 0]␤»
+
 
 =head1 Method postfix precedence