code: def addItem(self, child, href):
          
          assert isinstance(child, Base), "child must be a hypercat Catalogue or Resource"
          child.setHref(href)
          for item in self.items:
              assert item.href != href, "All items in a catalogue must have unique hrefs : "+href
          self.items += [child]           # Add new
          return
docs: Add a new item (a catalogue or resource) as a child of this catalogue.