def add_to_loader_class(cls, loader_class=None, tag=None, **kwargs):
        if tag is None:
            tag = ''
        tag = tag.strip()
        if not tag:
            tag = cls.DEFAULT_TAG_NAME
        if not tag.startswith('!'):
            raise ValueError('`tag` argument should start with character "!"')
        instance = cls(**kwargs)
        if loader_class is None:
            if FullLoader:
                yaml.add_constructor(tag, instance, FullLoader)
            else:
                yaml.add_constructor(tag, instance)
        else:
            yaml.add_constructor(tag, instance, loader_class)
        return instance