title: What can I do with an Transformable attribute type in Core Data on the iPhone?
body: <p>There's this Transformable data type for attributes. What is it good for? Are there good examples?</p>
  
  <p>I'd like to play around with this. So after searching a while I came across this: NSValueTransformer. Seems to be something I need for this.</p>
  
  <p>So how would I get started with this? For example, if I wanted to store an UIColor object, would I make an transformer for that?</p>
  
  <p>What exactly is this thing transforming to or from? An NSData? And must the object which I pass to the transformer follow any protocol?</p>