'Append an opening tag.'

def open(self, **kwargs):

    if ((self.tag in self.parent.twotags) or (self.tag in self.parent.onetags)):
        self.render(self.tag, False, None, kwargs)
    elif ((self.mode == 'strict_html') and (self.tag in self.parent.deptags)):
        raise DeprecationError(self.tag)
