title: Set a custom error message using the native rules of the knockout validation plugin
body: <p>I am using Asp.net MVC3 and knockoutjs library. I need to do some client side validation. I am exploring the knockout validation plugin. </p>
  
  <p>So I declare the following ko.observable value in my js code:</p>
  
  <pre><code> var numberValue = ko.observable().extend({ number: true }) 
  </code></pre>
  
  <p>This is my view part:</p>
  
  <pre><code>&lt;input data-bind = "value: numberValue " /&gt;
  </code></pre>
  
  <p>When the user enters some value that is not a number an error message is displayed : "Please enter a number". Can I display a different error message but still using the native rules?  I do not want to write custom validation logic just for this. Any help with some working example will be greatly appreciated. Thank You!</p>