What features can be used when installing sysrepo modules?

Question

To install a sysrepo module via code you can use the call sr_install_module() with the following parameters:

API int
sr_install_module(sr_conn_ctx_t *conn,
                  const char *schema_path,
                  const char *search_dirs,
                  const char **features)

Which options can be used for features in here?