title: How to set a parameter in PHP?
body: <p>In index.php page, I have this:</p>
  <pre><code>&lt;input type=&quot;hidden&quot; name=&quot;parent&quot; value=&quot;&lt;?php echo GROUP_ROOT_ID; ?&gt;&quot;&gt;
  </code></pre>
  <p><code>GROUP_ROOT_ID</code> is a macro, equaling to -1.</p>
  <p>If in xyz.php file, we check if the parameter parent has been set or not using the below code:</p>
  <pre><code>if (isset($_GET['parent'])) {
    //do something
  }
  </code></pre>
  <p>Why I cannot see parent has been set in xyz.php file? How can I make it be set?</p>
  <p>Thanks all!</p>