docs: function write_biff_rec(ba, t, payload, length) {
  	var len = (length || (payload||[]).length);
  	var o = ba.next(4 + len);
  	o.write_shift(2, t);
  	o.write_shift(2, len);
  	if(len > 0 && is_buf(payload)) ba.push(payload);
  }