title: waitpid with WUNTRACED
body: <p>Could someone please explain what the waitpid() call with the WUNTRACED option is used for? I understand that waitpid without any flags and -1 in the pid argument returns when a child exits. The manpage says </p>
  
  <pre><code> If the WUNTRACED option is set, children of the current process 
  that are stopped due to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signal 
  also have their status reported.
  </code></pre>
  
  <p>I do not see where this might be used. Thanks!</p>