Add the version(s) to the content to cache : internal version at first
        and then the template version if versioning is activated.
        Each version, and the content, are separated with `VERSION_SEPARATOR`.
        This method is called after the encoding (if "compress" or
        "compress_spaces" options are on)

def join_content_version(self, to_cache):
        """
        Add the version(s) to the content to cache : internal version at first
        and then the template version if versioning is activated.
        Each version, and the content, are separated with `VERSION_SEPARATOR`.
        This method is called after the encoding (if "compress" or
        "compress_spaces" options are on)
        """
        parts = [self.INTERNAL_VERSION]
        if self.options.versioning:
            parts.append(force_bytes(self.version))
        parts.append(force_bytes(to_cache))

        return self.VERSION_SEPARATOR.join(parts)