title: Save file with mac application - file extension
body: <p>I have a little question, I try to understand how to save a file with Cocoa for a Mac application, I understand that I can save it with a Save Panel.</p>
  
  <p>Here is a great example: 
  <a href="https://stackoverflow.com/questions/2933255/saving-files-in-cocoa">Saving files in cocoa</a></p>
  
  <p>Now my question is, is there a way to save the document (a plst file) with a my extension (eg. *.fun, *.xxx, *.myextension, ecc...)? I want to be able to open my application when the user double clicks on the file.</p>