Adds the Boolean bitwise XOR operator

Which was not documented. That closes #2939

Author: JJ

doc/Language/operators.pod6

@@ -1034,10 +1034,8 @@ Please note that this has not yet been implemented.
 
     multi sub prefix:<?^>(Mu --> Bool:D)
 
-X<Boolean bitwise negation operator>.
-
-Coerces the argument to L<Bool|/type/Bool> and then does a bit flip, which makes it the
-same as C<< prefix:<!> >>.
+X<Boolean bitwise negation operator>: Coerces the argument to L<Bool|/type/Bool>
+and then does a bit flip, which makes it the same as C<< prefix:<!> >>.
 
 =head2 prefix C«^»
 
@@ -1236,6 +1234,15 @@ Coerces each argument to a non-variable-encoding string buffer type (e.g. C<buf8
 and then performs a numeric bitwise XOR on corresponding integers of the two buffers, padding the
 shorter buffer with zeroes.
 
+=head2 infix C«?^»
+
+    multi sub infix:<?^>(Mu $x = Bool::False)
+    multi sub infix:<?^>(Mu \a, Mu \b)
+
+X<Boolean bitwise XOR operator>: Coerces the argument(s) to L<Bool|/type/Bool>
+and performs logical XOR on them: it will return True if and only if just one of
+the argument is true. It returns identity on a single argument.
+
 =head2 infix C«?|»
 
     multi sub infix:<?|>($a, $b --> Bool:D)