title: Force browser to re-read cached images
body: <p>.button {
          background: url(../Images/button.png);
      }</p>
  
  <p><strong>Problem:</strong> for performance reason all static content has expiration headers and is cached by browser.  When image changes user must refresh cache (Ctrl+F5 in IE). I want images to be cached, but when necessary they must be automatically reloaded.</p>
  
  <p><strong>Question:</strong> is next approach 'valid'?</p>
  
  <pre><code>.button {
      background: url(../Images/button.png?v=1234);
  }
  </code></pre>
  
  <p>where v=1234 is version of my site. I do not know whether it is 100% valid to write such things in CSS and I do want browsers to still cache images if version is the same. Do all modern browsers correctly cache data with URL parameters part?</p>
  
  <p>Thanks.</p>