anchor.diff:          name = "float";
           description = "floating point number";
           check = isFloat;
  -        merge = mergeOneOption;
  +        merge = mergeEqualOption;
       };
   
       str = mkOptionType {
         name = "str";
         description = "string";
         check = isString;
  -      merge = mergeOneOption;
  +      merge = mergeEqualOption;
       };
   
       strMatching = pattern: mkOptionType {
  
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 = "int";
          description = "signed integer";
          check = isInt;
          merge = mergeEqualOption;
        };
  
      # Specialized subdomains of int
  