type: X around xref not C

Author: ajs

doc/Language/regexes.pod6

@@ -305,7 +305,7 @@ you:
 To match the unmodified character, you can use the
 L<C<:ignoremark>|#regex adverb,:ignoremark> adverb.
 
-=head3 C<C<\x> and C<\X>|regex,\x;regex,\X>
+=head3 X<C<\x> and C<\X>|regex,\x;regex,\X>
 
 C<\x> takes a paramter delimited by square-brackets which is the
 hexadecimal representation of the Unicode codepoint representing the