Things that are there but you cannot use

I did a “desc” command on the STANDARD package today, the package that helps define PL/SQL, and saw the XOR function!

SQL> declare
  2    x boolean;
  3  begin
  4    x := XOR(true,true);
  5    dbms_output.put_line(case when x then 'TRUE' else 'FALSE' end);
  6
  7    x := XOR(true,false);
  8    dbms_output.put_line(case when x then 'TRUE' else 'FALSE' end);
  9
 10    x := XOR(false,false);
 11    dbms_output.put_line(case when x then 'TRUE' else 'FALSE' end);
 12
 13  end;
 14  /
FALSE
TRUE
FALSE

PL/SQL procedure successfully completed.

I cant find any reference to it in the Oracle PL/SQL documentation anywhere, so its definitely not supported so using it is probably off limits until you see officially in the documentation.