'Append a closing tag unless element has only opening tag.'

def close(self):

    if (self.tag in self.parent.twotags):
        self.parent.content.append(('</%s>' % self.tag))
    elif (self.tag in self.parent.onetags):
        raise ClosingError(self.tag)
    elif ((self.parent.mode == 'strict_html') and (self.tag in self.parent.deptags)):
        raise DeprecationError(self.tag)
