title: What's the proper format for the "date" datatype?
body: <p>My model "User" has a date attribute <code>:birthday</code>. But if I submit a birthday with any format other than <code>x/x/x</code>, it just becomes nil. So, for example, <code>1/1/1</code> becomes "0001-01-01", but <code>1/1/15</code> becomes nil. <code>1/1/2</code> becomes "0001-01-02", but <code>22/1/3</code> becomes nil.</p>
  
  <p>I feel like I'm missing something here. It can't possibly be true that date attributes can only be <code>x/x/x</code>, right?</p>