docs: private int endCheckIf()
      {
          Node th, el;
          int rv = END_UNREACHED;
  
          th = next;
          el = ((Jump)this).target;
  
          rv = th.endCheck();
  
          if (el != null)
              rv |= el.endCheck();
          else
              rv |= END_DROPS_OFF;
  
          return rv;
      }