title: How do I set caching headers for my CSS/JS but ensure visitors always have the latest versions?
body: <p>I'd like to speed up my site's loading time in part by ensuring all CSS/JS is being cached by the browser, as recommend by Google's PageSpeed tool.  But I'd like to ensure that visitors have the latest CSS/JS files, if they are updated and the cache now contains old code.  </p>
  
  <p>From my research so far, appending something like "?459454" to the end of the CSS/JS url is popular.  But wouldn't that force the visitor's browser to re-download the CSS/JS file every time?</p>
  
  <p>Is there a way to set the files to be cached by the browser, but ensure the browser knows about updated versions of the cached files?</p>