docs: def add_unique_element(self, location, element):
          """
          Create an entry located at ``location``.
          
          Args:
              location: String or :class:`LocationDescriptor` to describe a "separator location" (i.e. dir1/dir2/dir3 for
                  instance).
              element: Element to store.
          
          Returns:
              The created node with the element.
  
          Notes:
              The different sub locations entries **must** exist and the last one **MUST NOT** already exist.
              Use the more loose :meth:`add_element` method if needed.
          """
          return self._create_entry(location, element, unique=True)