anchor.diff:          name = "int";
           description = "signed integer";
           check = isInt;
  -        merge = mergeOneOption;
  +        merge = mergeEqualOption;
         };
   
       # Specialized subdomains of int
  
positive.code:       name = "path";
        # Hacky: there is no ‘isPath’ primop.
        check = x: builtins.substring 0 1 (toString x) == "/";
        merge = mergeOneOption;
      };
  
      # drop this in the future:
  
negative.code:         name = "enum";
          description = "one of ${concatMapStringsSep ", " show values}";
          check = flip elem values;
          merge = mergeEqualOption;
          functor = (defaultFunctor name) // { payload = values; binOp = a: b: unique (a ++ b); };
        };
  
  