r"""Build started tag info.

        :param tag: tag name
        :param attrs: tag attributes. Default：``None``.
        :type attrs: dict or None
        :rtype: str

def tag_start(self, tag, attrs=None):
        r"""Build started tag info.

        :param tag: tag name
        :param attrs: tag attributes. Default：``None``.
        :type attrs: dict or None
        :rtype: str
        """
        return '<%s %s>' % (tag, self.build_attr(attrs)) if attrs else '<%s>' % tag