code: function(walk) {
      return this.tryBracing(walk, '```', '```', function(w) {
        this.out.push("<code>");
        while (w.hasCurrent())
          this.emitPlain(w);
        this.out.push("</code>");
      });
    }
docs: /* Triple code spans are emitted as is, only ampersands are escaped
  inside.