The underline type corresponding to the ``w:val`` attribute value.

def val(self):
        """
        The underline type corresponding to the ``w:val`` attribute value.
        """
        val = self.get(qn('w:val'))
        underline = WD_UNDERLINE.from_xml(val)
        if underline == WD_UNDERLINE.SINGLE:
            return True
        if underline == WD_UNDERLINE.NONE:
            return False
        return underline