code: void deliver(final OtpMsg m) {
          switch (m.type()) {
          case OtpMsg.linkTag:
              links.addLink(self, m.getSenderPid());
              break;
  
          case OtpMsg.unlinkTag:
              links.removeLink(self, m.getSenderPid());
              break;
  
          case OtpMsg.exitTag:
              links.removeLink(self, m.getSenderPid());
              queue.put(m);
              break;
  
          case OtpMsg.exit2Tag:
          default:
              queue.put(m);
              break;
          }
      }
docs: /*
  called by OtpNode to deliver message to this mailbox.
  
  About exit and exit2: both cause exception to be raised upon receive().
  However exit (not 2) causes any link to be removed as well, while exit2
  leaves any links intact.