%!demo
%! ## Concatenating categorical arrays *unions* their category lists, so the result
%! ## can hold categories that neither operand had alone.  `[A; B]` stacks them.
%!
%! A = categorical ({'S'; 'M'})
%! B = categorical ({'L'; 'XL'})
%! C = [A; B];
%! C
%! categories (C)
