What sort of issue would generate an E_COMPILE_WARNING in PHP?
<p>I've spent a bit searching <em>The Google</em> as well as <em>SO</em> and have been unable to find an answer for this simple question:</p>

<h2>What sort of issue would generate an <code>E_COMPILE_WARNING</code> in PHP?</h2>

<p>The <a href="http://www.php.net/manual/en/errorfunc.constants.php" rel="nofollow"><strong>PHP manual entry on the subject</strong> <sup><em>docs</em></sup></a> says of <code>E_COMPILE_WARNING</code>:</p>

<blockquote>
  <p>Compile-time warnings (non-fatal errors). This is like an E_WARNING,
  except it is generated by the Zend Scripting Engine.</p>
</blockquote>

<p>But I'm not sure what this would constitute. What's the difference between a regular <code>E_WARNING</code> and a warning raised by the Zend Scripting Engine? Could someone please explain and provide a code snippet if applicable?</p>
