title: How do I flag a folder as being a package?
body: <p>I used to think that folders needed to have an extension so that they are recognized as packages by the Finder. That extension would be declared in the owning application's Info.plist.</p>
  
  <p>Obviously there is another, more elegant way, but I can't figure out how it is done.</p>
  
  <p>E.g. the iPhoto Library is being treated as a package by the Finder. Yet it has no extension. mdls reveals that it indeed has "com.apple.package" in the content type tree. The actual content type is dynamically assigned.</p>
  
  <p>How did iPhoto go about to create such a directory?</p>