Tweak Repetition operator.

For coherence with the perlop Perl 5 documentation all references
have been adjusted to 'Repetition'. I've split the reminder of how
Perl 5 'x' worked in string and list context and then presented the same
items for Perl 6 'x' and 'xx'.

Author: fluca1978

doc/Language/5to6-nutshell.pod6

@@ -718,17 +718,19 @@ Mnemonic: think of "stitching" together the two strings with needle and thread.
 =for code :preamble<no strict;>
     $food = 'grape' ~ 'fruit'; # Perl 6
 
-=head2 C<x> List Repeat op or String Repeat op
+=head2 C<x> List Repetition or String Repetition operator
 
-In Perl 5, C<x> was the Repetition operator.
+In Perl 5, C<x> is the Repetition operator, which behaves differently in
+scalar or list contexts:
+=item in scalar context C<x> repeats a string;
+=item in list context C<x> repeats a list, but only if the left argument
+is parenthesized!
 
-In scalar context, C<x> would repeat a string. In Perl 6, C<x> repeats
-strings in any context.
+Perl 6 uses two different Repetition operators to achieve the above:
+=item C<x> for string repetitions (in any context);
+=item C<xx> for list repetitions (in any context).
 
-In list context, C<x> would repeat a list—but only if the left argument
-is parenthesized! In Perl 6, the new C<xx> op repeats lists in any context.
-
-Mnemonic: x is short and xx is long, so xx is the one used for lists.
+Mnemonic: C<x> is short and C<xx> is long, so C<xx> is the one used for lists.
 
 =for code :lang<perl5>
     # Perl 5