what is double(::) in angular js? : <p>While going through some of the angular best practices guide I found this concept of using <code>::</code> before models for uni-direction binding. But it seems does not work with <code>input</code> field. Here is an example:</p>

<p><a href="https://plnkr.co/edit/gZ73PNGGg4m45zFuBYZw?p=preview" rel="nofollow">https://plnkr.co/edit/gZ73PNGGg4m45zFuBYZw?p=preview</a></p>

<p>Inside expression it works as expected but inside ng-model, it's still 2-way binding. Then what's the difference?</p>
