What values of error_code can a boost timer callback receive?

Question

Like many asio callbacks asio timer callbacks take argument

const boost::system::error_code&

I am curios if it is documented what are possible values for that argument, since from my naive understanding of reading header documentation only one value beside success is possible.

void on_timeout(const boost::system::error_code& e)
{
  if (e != boost::asio::error::operation_aborted)
  {
    // Timer was not cancelled, take necessary action.
   }
 }