title: Correct way of binding multiple attribute changes to a Backbone.js model
body: <p>I have the following code, where I bind a change to a single attribute "attribute_1". </p>
  
  <pre><code>var Mine = Backbone.Model.extend({
    initialize: function() {
      this.bind("change:attribute_1", function() {
        console.log('changed!');
      });
    }
  });
  </code></pre>
  
  <p>How do I bind two attributes? This doesn't work:</p>
  
  <pre><code>var Mine = Backbone.Model.extend({
    initialize: function() {
      this.bind("change:attribute_1, change:attribute_2", function() {
        console.log('changed!');
      });
    }
  });
  </code></pre>
  
  <p>Nor does this:</p>
  
  <pre><code>var Mine = Backbone.Model.extend({
    initialize: function() {
      this.bind("change:attribute_1 change:attribute_2", function() {
        console.log('changed!');
      });
    }
  });
  </code></pre>