Add new tokens to list.

def add(self, *tokens: str) -> None:
        """Add new tokens to list."""
        from wdom.web_node import WdomElement
        _new_tokens = []
        for token in tokens:
            self._validate_token(token)
            if token and token not in self:
                self._list.append(token)
                _new_tokens.append(token)
        if isinstance(self._owner, WdomElement) and _new_tokens:
            self._owner.js_exec('addClass', _new_tokens)