title: How to tell if a timezone observes daylight saving at any time of the year?
body: <p>In PHP, you can tell if a given date is during the Daylight Savings Time period by using something like this:</p>
  
  <pre><code>$isDST = date("I", $myDate); // 1 or 0
  </code></pre>
  
  <p>The problem is that this only tells you whether that one point in time is in DST. Is there a reliable way to check whether DST is in effect at any time in that timezone?</p>
  
  <hr>
  
  <p><em>Edit to clarify:</em></p>
  
  <ul>
  <li>Brisbane, Australia does not observe daylight savings at any time of the year. All year around, it is GMT+10.</li>
  <li>Sydney, Australia does, from October to March when it changes from GMT+10 to GMT+11.</li>
  </ul>
  
  <p>I'm wondering if there would be some existing method, or a way to implement a method which works as such:</p>
  
  <pre><code>timezoneDoesDST('Australia/Brisbane');  // false
  timezoneDoesDST('Australia/Sydney');  // true
  </code></pre>