anchor.diff:          foldProperty
             (foldFilter isOverride
               (p@{property, content, ...}:
  -              if lessThan content.priority property.priority then
  +              if content ? priority && lessThan content.priority property.priority then
                   content
                 else
                   content // {
  
positive.code:                 value = p // { content = content.value; };
                }
              )
            ) (value: { priority = defaultPrio; inherit value; });
  
        prioValList = map getPrioVal valList;
  
        higherPrio = fold (x: y:
          if lessThan x.priority y then
            x.priority
          else
            y
        ) defaultPrio prioValList;
      in
        map (x:
          if x.priority == higherPrio then
  
negative.code:     inherit content;
    };
  
    # Sugar to override the default value of the option by making a new
    # default value based on the configuration.
    mkDefaultValue = content: mkOverride 1000 {} content;
  
    # Make the template traversal in function of the property traversal.  If
    # the template define a non-empty attribute set, then the property is
    # copied only on all mentionned attributes inside the template.
  