def composite_join(separator, items):
        """
        Join a list of items with a separator.
        This is used in joining strings, responses and Composites.
        The output will be a Composite.
        """
        output = Composite()
        first_item = True
        for item in items:
            # skip empty items
            if not item:
                continue
            # skip separator on first item
            if first_item:
                first_item = False
            else:
                output.append(separator)
            output.append(item)
        return output
Join a list of items with a separator.
        This is used in joining strings, responses and Composites.
        The output will be a Composite.