title: Code Inspection in PhpStorm
body: <p>PhpStorm does not detect undefined variables, when they are passed to a function by reference.</p>
  
  <pre><code>func1($a);
  func2($a);
  
  function func1(&amp;$a) {
  }
  function func2($a) {
  }
  </code></pre>
  
  <p>In this example, only the variable <code>$a</code> in the invocation of <code>func2</code> is highlighted.</p>
  
  <p>How can I change that?</p>