title: Knockout style binding with three options
body: <p>Alright, so I have used the KO style binding extensively to show inline-validation of user inputted data, and it works great.  Here's one of my bindings: </p>
  
  <pre><code>data-bind='style: {backgroundPosition: ! currentRegistry().title() || !$root.currentRegistry().clientLogin()  ? "top" : "bottom"}
  </code></pre>
  
  <p>The trouble I'm having is that I want to do a binding like this, except that on the second style binding, if the if statement evaluates to false I'd like it to return to whatever background position was set by the previous binding, rather than just going back to "bottom": </p>
  
  <pre><code>data-bind='style: {backgroundPosition: ! currentRegistry().title() || !$root.currentRegistry().clientLogin()  ? "top" : "bottom"}, style: {backgroundPosition: currentRegistry().title() &amp;&amp; $root.currentRegistry().clientLogin() &amp;&amp; ! $root.hasRegImage()  ? "20px" : "bottom"}'
  </code></pre>
  
  <p>In other words, for the second binding I'd like to say style: {backgroundPosition: if stuff ? "THIS"} else don't change the style.  Hope that makes sense, any hints or pointers to make this happen would be greatly appreciated!  Thanks.</p>
  
  <p>Edit:  </p>
  
  <p>Although RodneyTrotter's solution is undoubtedly the more elegant way to get this same functionality, I did learn a method from a colleague that does EXACTLY what I was asking.  I didn't realize that you could make each property conditional, aka: </p>
  
  <pre><code>data-bind='style: {backgroundPosition: ! $root.currentRegistry().clientLogin() || ! $root.currentRegistry().title()  ? "top" :  (! $root.hasRegImage()  ? "20px" : "bottom")}'&gt;
  </code></pre>