title: How to validate content of an <input> tag in EmberJS
body: <p>I've defined an input field in one of my Handlebars template as follows:</p>
  
  <pre><code>&lt;input {{bind-attr value=stratName}}&gt;
  </code></pre>
  
  <p>I didn't want to use this:</p>
  
  <pre><code>{{input value=stratName}}
  </code></pre>
  
  <p>because I want to run a validation function against user input before the new value is copyied to the model.</p>
  
  <p>What's the easiest way to attach a validation function, triggered on focusOut, on the input tag?  I also want to keep the user from leaving the field until a valid input is detected?</p>