Hirarchy
========

* group property (currently a identifier like string, may be extended to tree like substrucutres by allowing ':')
* visibility (enum(3:expert, 2:advanced, 1:user)) (default to 1 if not given)
  if visibility is set to user: everybody should see it
  if visibility is set to advanced: advanced users should see it
  if visibility is set to expert: only 'experts' should see it