title: Backbone.js - id vs idAttribute vs cid
body: <p>I've been studying Backbone.js for a few weeks, and I feel comfortable using views with models, routers, and collections. </p>
  
  <p>I still have some big gaps:</p>
  
  <ol>
  <li><p>What is the connection between <code>id</code>, <code>cid</code>, and <code>idAttribute</code>? How do they affect each other?</p></li>
  <li><p>When exactly does a new model get its ID? Is the server responsible for assigning it? Do I need to add it to the <code>defaults</code> of the model (maybe as a function)? Maybe the <code>addNewModel</code> function should do that?</p></li>
  </ol>