title: Is it possible to search the SESSIONs across multiple visitors
body: <p>A SESSION is created for each website visitor. </p>
  
  <p>Some visitors have <code>$_SESSION['reference'] = "foo"</code> others have <code>$_SESSION['reference'] = "bar"</code>.</p>
  
  <p><code>$number_of_visitors = count(scandir(ini_get("session.save_path")));</code> counts the number of sessions but does not test for <code>'reference' = "foo"</code>. </p>
  
  <p><code>$number_of_foo_visitors = count($_SESSION['foo']);</code> only counts 1 (ie. myself) because it is limited to only that visitor's session data. What it does not count is all current sessions where <code>'reference' = "foo"</code>  </p>
  
  <p>Is it possible to count across all visitors SESSIONs where <code>$_SESSION['reference'] = "foo"</code>? </p>