Improves documentation and examples for Mix

The example for the second case was reproduced over and over, but it
didn't behave the same in the first example, so I have changed it to a
new one and explains behavior. Also adds another example for `is`,
which uses a different mechanism, `STORE`

Closes #2459

doc/Type/Mix.pod6

@@ -44,9 +44,10 @@ C<Mix.new>, for which it is a shorthand). Any positional parameters,
 regardless of their type, become elements of the mix - with a weight of
 C<1> for each time the parameter occurred:
 
-    my $n = mix "a", "a", "b" => 0, "c" => 3.14;
-    say $n.keys.map(&WHAT);  # OUTPUT: «((Str) (Pair) (Pair))␤»
-    say $n.pairs;            # OUTPUT: «(a => 2 (c => 3.14) => 1 (b => 0) => 1)␤»
+    my $n = mix "a", "a", "b" => 0, 3.14, π, π; # The Pair is a single element
+    say $n.keys.map: *.^name; # OUTPUT: «(Rat Pair Num Str)␤»
+    say $n.pairs;
+    # OUTPUT: «(3.14 => 1 (b => 0) => 1 3.141592653589793 => 2 a => 2)␤»
 
 Alternatively, the C<.Mix> coercer (or its functional form, C<Mix()>)
 can be called on an existing object to coerce it to a C<Mix>. Its
@@ -60,6 +61,15 @@ values become the associated numeric weights:
     say $n.keys.map(&WHAT);  # OUTPUT: «((Str) (Str))␤»
     say $n.pairs;            # OUTPUT: «(a => 2 c => 3.14)␤»
 
+Elements with a 0 value, as C<b> above, are simply eliminated from the C<Mix>.
+
+Alternatively, since C<Mix>es are L<Associative>, we can use the C<%> sigil to
+declare them; in that case, we can employ C<is> to declare their type:
+
+    my %n is Mix = ("a", "a", "b" => 0, "c" => 3.14);
+    say %n.^name; # OUTPUT: «Mix␤»
+    say %n;       # OUTPUT: «Mix(a(2), c(3.14))␤»
+
 =head1 Operators
 
 C<Mix>es can use all kind of set operators returning either C<Bool> or