anchor.diff:                  (pushDownProperties (getAttr name m.config)))
               ) configs);
             nrOptions = count (m: isOption m.options) decls;
  -
  -          defns2 = concatMap (m:
  -            optional (hasAttr name m.config)
  -              { inherit (m) file; config = getAttr name m.config; }
  +          # Process mkMerge and mkIf properties.
  +          defns' = concatMap (m:
  +            optionals (hasAttr name m.config)
  +              (map (m': { inherit (m) file; value = m'; }) (dischargeProperties (getAttr name m.config)))
               ) configs;
           in
             if nrOptions == length decls then
               let opt = fixupOptionType loc' (mergeOptionDecls loc' decls);
  -            in evalOptionValue loc' opt defns2
  +            in evalOptionValue loc' opt defns'
             else if nrOptions != 0 then
               let
                 firstOption = findFirst (m: isOption m.options) "" decls;
  
positive.code:   filterOverrides = defs:
      let
        defaultPrio = 100;
        getPrio = def: if def.config._type or "" == "override" then def.config.priority else defaultPrio;
        min = x: y: if x < y then x else y;
        highestPrio = fold (def: prio: min (getPrio def) prio) 9999 defs;
        strip = def: if def.config._type or "" == "override" then def // { config = def.config.content; } else def;
      in concatMap (def: if getPrio def == highestPrio then [(strip def)] else []) defs;
  
    /* Hack for backward compatibility: convert options of type
  
negative.code: 
    /* Merge all the definitions of an option to produce the final
       config value. */
    evalOptionValue = loc: opt: defs:
      let
        # Process mkOverride properties, adding in the default
        # value specified in the option declaration (if any).
        defsFinal = filterOverrides (optional (opt ? default) ({ file = head opt.declarations; value = mkOptionDefault opt.default; }) ++ defs);
        # Type-check the remaining definitions, and merge them if
        # possible.
        merged =
  