code: def _fetch_itemslist(self, item):
          
          if item.is_root:
              for c in ["Arbetsolycka", "Arbetssjukdom"]:
                  yield Collection(c, blob=(c, None, None))
          else:
              c = item.id
              for r in [u"kommun", u"län"]:
                  for p in [u"år", u"månad"]:
                      yield Dataset(u"%s-%s-%s" % (c, r, p),
                                    blob=(c, r, p),
                                    label=u"%s, antal per %s och %s" % (c, r, p))
docs: We define two collection:
          - Number of work injuries ("Arbetsolycka")
          - Number of workrelated diseases ("Arbetssjukdom")
          Each contains four datasets:
          - Per municipality and year
          - Per county and year
          - Per municipality and month
          - Per municipality and year