docs: def kadd(self, key, value):
          """Adds the given key/value to all elements.
          Single values for a key are stored directly, as key:value, multiple
          values for the same key are stored as key,set(values).
          """
          for item in self:
              try:
                  # Use the key as a set
                  item[key].add(value)
              except KeyError:
                  # This happens if the key is not present
                  item[key] = value
              except AttributeError:
                  # This happens if the key is present but is not a set
                  item[key] = set([item[key], value])