def output_footnote(self):
        self.inline._in_footnote = True
        body = self.renderer.placeholder()
        key = self.token['key']
        while self.pop()['type'] != 'footnote_end':
            body += self.tok()
        self.footnotes.append({'key': key, 'text': body})
        self.inline._in_footnote = False
        return self.renderer.placeholder()