title: Knockout.js how do i bind to a sub property
body: <p>I know how to bind to a property, but how do i bind to a property like:
  Parent.Child</p>
  
  <p>Using the hello world example on Knockout JS.com:
  Html:</p>
  
  <pre><code>&lt;p&gt;First name: &lt;input data-bind="value: firstName" /&gt;&lt;/p&gt;
  &lt;p&gt;Last name: &lt;input data-bind="value: lastName" /&gt;&lt;/p&gt;
  &lt;h2&gt;Hello, &lt;span data-bind="text: fullName"&gt; &lt;/span&gt;!&lt;/h2&gt;
  &lt;h2&gt;ChildProperty: &lt;span data-bind="text: parentProperty.childProperty"&gt; &lt;/span&gt;!&lt;/h2&gt;
  </code></pre>
  
  <p>Javascript:</p>
  
  <pre><code>var ViewModel = function(first, last) {
  this.firstName = ko.observable(first);
  this.lastName = ko.observable(last);
  this.parentProperty = ko.observable(
      {
          childProperty: "I am a child Property"
      });
  
  this.fullName = ko.computed(function() {
      // Knockout tracks dependencies automatically. It knows that fullName depends on firstName      and lastName, because these get called when evaluating fullName.
          return this.firstName() + " " + this.lastName();
      }, this);
  };
  
  ko.applyBindings(new ViewModel("Planet", "Earth"));
  </code></pre>
  
  <p>I would like to create a binding to the childProperty.</p>
  
  <p>I created a <a href="http://jsfiddle.net/szk2e/1/" rel="noreferrer">jsfiddle here</a></p>
  
  <p>Thanks</p>