title: knockout.js get parent observable
body: <p>Is it possible to get parent observable in knockout? Like I have</p>
  
  <pre><code>&lt;div data-bind="parent: {...}"&gt;
     &lt;div data-bind="child: {...}"&gt;
        ...
     &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I want to get access to parent in child <strong>but not in the markup but in the code</strong>. How can I achieve in a standard knockout way?</p>
  
  <p><strong>UPDATE</strong>
  I have found a simple way to achieve this by simply accessing the last argument of custom handler like this:</p>
  
  <pre><code>ko.bindingHandlers.custom = {
    init: function (element, valueAccessor, allBindingsAccessor, vm, bindingContext) {
       console.log(bindingContext.$parent);
    }
  }
  </code></pre>