%!demo
%! ## `iscategory` tests whether names are categories of the array — independently
%! ## of whether any element currently takes those values.
%!
%! C = categorical ({'M'; 'S'}, {'S', 'M', 'L'})
%! iscategory (C, {'M', 'L', 'XL'})
%!
%! ## `M` and `L` are declared categories; `XL` is not.
