title: asp.net mvc 5 - StyleBundle CdnFallbackExpression questions?
body: <p>I've added bootstrap CSS files via a StyleBundle to my asp.net mvc 5 project.</p>
  
  <p>(It uses as Cdn: <a href="https://www.asp.net/ajax/cdn#Bootstrap_Releases_on_the_CDN_14" rel="noreferrer">https://www.asp.net/ajax/cdn#Bootstrap_Releases_on_the_CDN_14</a> )</p>
  
  <pre><code>  var bootstrapCssCdnPath = "http://ajax.aspnetcdn.com/ajax/bootstrap/3.3.7/css/bootstrap.min.css";
    var bootstrapCssBundle = new StyleBundle("~/bundles/css/bootstrap", bootstrapCssCdnPath).Include("~/Content/bootstrap.css");
    //bootstrapCssBundle.CdnFallbackExpression // ?
    bundles.Add(bootstrapCssBundle);
  
    var bootstrapThemeCssCdnPath = "http://ajax.aspnetcdn.com/ajax/bootstrap/3.3.7/css/bootstrap-theme.min.css";
    var bootstrapThemeCssBundle = new StyleBundle("~/bundles/css/bootstraptheme", bootstrapThemeCssCdnPath).Include("~/Content/bootstrap-theme.css");
    //bootstrapCssBundle.CdnFallbackExpression // ?
    bundles.Add(bootstrapThemeCssBundle);
  </code></pre>
  
  <p>However there is a problem: when I add an incorrect url as CDN (e.g. adding 'ahttp' instead of 'http') my custom "fallback" css file is not used, instead it shows 'ahttp://' in my html source.
  Same when I'm running my site on Debug or Release.</p>
  
  <ol>
  <li>Why is my fallback not being used?</li>
  <li>What is the CdnFallbackExpression for a StyleBundle? (and in particular for a bootstrap.css and bootstrap-theme.css)</li>
  <li>Should the .Include be the .min.css file or does it automatically search for the .min. version first?</li>
  <li>Is there a way to .Include multiple css files, using a Cdn with fallback, so that I don't have to create a new StyleBundle everytime per css file that uses a Cdn?</li>
  </ol>