def set_metadata(self, metadata, clear=False, prefix=None):
        """
        Accepts a dictionary of metadata key/value pairs and updates the
        specified container metadata with them.

        If 'clear' is True, any existing metadata is deleted and only the
        passed metadata is retained. Otherwise, the values passed here update
        the container's metadata.

        The 'extra_info' parameter is included for backwards compatibility. It
        is no longer used at all, and will not be modified with swiftclient
        info, since swiftclient is not used any more.

        By default, the standard container metadata prefix
        ('X-Container-Meta-') is prepended to the header name if it isn't
        present. For non-standard headers, you must include a non-None prefix,
        such as an empty string.
        """
        return self.manager.set_metadata(self, metadata, clear=clear,
                prefix=prefix)