Make C<$> explanation a little clearer

It seemed that the anonymous state variable was a bit lost in the
rest of the state variable discussion so it merited a section of its
own. Also clarify that each reference is a separate variable.

doc/Language/variables.pod

@@ -552,20 +552,22 @@ called. So it will output
 
 =end code
 
-As seen in this example, C<$> can be used as an anonymous state variable
-without an explicit C<state> declaration.
-
 As with C<my>, declaring multiple C<state> variables must be placed
 in parentheses and for declaring a single variable, parentheses may
 be omitted.
 
+=head3 The C<$> Variable
+
+As well as explicitly declared named state variables C<$> can be used
+as an anonymous state variable without an explicit C<state> declaration:
+
 =begin code
 
 perl6 -e 'sub foo() { say ++$  }; foo() for ^3'
 
 =end code
 
-produces
+produces:
 
 =begin code
 
@@ -575,26 +577,28 @@ produces
 
 =end code
 
-Furthermore, state variables are not required to exist in
-subroutines. You could, for example, use C<$> in a one-liner to
-number the lines in a file.
+There is no L<Positional> (C<@>) or L<Associative> (C<%>) equivalent, so a
+named state variable must be used for those cases.
+
+Furthermore, state variables are not required to exist in subroutines. You
+could, for example, use C<$> in a one-liner to number the lines in a file:
 
 =begin code
 
 perl6 -ne 'say ++$ ~ " $_"' example.txt
 
 =end code
 
-Finally, if you were to use multiple anonymous state variables, they would
-fuction independently.
+Each reference to C<$> within a lexical scope in effect is a separate
+variable, as illustrated by:
 
 =begin code
 
 perl6 -e '{ say ++$; say $++  } for ^5'
 
 =end code
 
-would produce
+which produces:
 
 =begin code
 
@@ -611,6 +615,38 @@ would produce
 
 =end code
 
+If you need to refer to the value of C<$> more than once within the
+scope it should be copied to a new variable, for example:
+
+=begin code
+sub foo() {
+    given ++$ {
+        when 1 {
+            say "one";
+        }
+        when 2 {
+            say "two";
+        }
+        when 3 {
+            say "three";
+        }
+        default {
+            say "many";
+        }
+    }
+}
+
+foo() for ^3;
+=end code
+
+produces:
+
+=begin code
+one
+two
+three
+=end code
+
 =head2 The C<augment> Declarator
 
 With C<augment>, you can add attributes and methods to existing classes and