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.

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)