in source/ext/extref.py [0:0]
def config_inited_handler(app, config):
if config.extref_default_type and not config.extref_default_type in REF_TYPES:
raise ValueError("Parameter extref_default_type should be in {0}".format(REF_TYPES))
prepare_conf_json(app, config)
prepare_images(app, config)