title: scala colon right arrow key vs only colon
body: <p>In Play scala html template, one can specify</p>
  
  <blockquote>
    <p>@(title: String)(content: Html)</p>
  </blockquote>
  
  <p>or</p>
  
  <blockquote>
    <p>@(title: String)(content: => Html)</p>
  </blockquote>
  
  <p>What is the difference?</p>