title: Rules for "Date Modified" of folders in Windows Explorer
body: <p>How does Windows Explorer determine the "Date Modified" field for folders? <i>[Aside: I know this is asking from an explorer-specific perspective, but the behaviour could be useful to coding search/sort type activities]</i></p>
  
  <p>Is there a definitive description of this anywhere - searches of Microsoft, MSDN, Google &amp; Stack Overflow have been unsuccessful.</p>
  
  <p>Personal experiments seem to suggest that in a tree of folders:</p>
  
  <ol>
  <li>when a folder/file is added/deleted in a folder, the <b>containing folder's</b> date modified is updated.</li>
  <li>when the content of a file is modified, the containing folder is unaffected</li>
  </ol>
  
  <p>However, I'm looking at some directories that don't seem to conform to these basic rules - running down the tree I have (dates in DD/MM/YYYY format):</p>
  
  <pre><code>folder     (date created:  2/2/2006, date modified: 2/3/2006)
    folder   (date created:  2/2/2006, date modified: 2/3/2006)
      folder (date created:  2/2/2006, date modified: 1/6/2009)
        file (date created: 27/3/2009, date modified: 2/2/2006)
  </code></pre>