anchor.diff:                ).optionalValue
               ) def.value
             else
  -            throw "The option value `${showOption loc}' in `${def.file}' is not a list.") defs)));
  +            throw "The option value `${showOption loc}` in `${def.file}` is not a list.") defs)));
         getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["*"]);
         getSubModules = elemType.getSubModules;
         substSubModules = m: listOf (elemType.substSubModules m);
  
positive.code:         let nrNulls = count (def: def.value == null) defs; in
          if nrNulls == length defs then null
          else if nrNulls != 0 then
            throw "The option `${showOption loc}' is defined both null and not null, in ${showFiles (getFiles defs)}."
          else elemType.merge loc defs;
        getSubOptions = elemType.getSubOptions;
        getSubModules = elemType.getSubModules;
  
negative.code:         merge = mergeOneOption;
        };
  
      # Specialized subdomains of int
      ints =
        let
          betweenDesc = lowest: highest:
  