%!demo
%! ## `isprotected` reports whether the category list is locked.  A nominal array
%! ## is *unprotected*: assigning a new label simply extends its categories ...
%!
%! N = categorical ({'M'; 'S'})
%! isprotected (N)
%!
%! ## ... whereas ordinal arrays (and ones built with `'Protected', true`) are
%! ## protected, so only their declared categories may be used.
%!
%! O = categorical ({'M'; 'S'}, {'S', 'M', 'L'}, 'Ordinal', true)
%! isprotected (O)
