&gt; Facebook, like many sites, uses versioned URLs - these URLs are never updated to have different content and instead the site changes the subresource URL itself when the content changes. This is a common design pattern...<p>Why not use the ETag header instead? <a href="https:&#x2F;&#x2F;www.w3.org&#x2F;Provider&#x2F;Style&#x2F;URI.html" rel="nofollow">https:&#x2F;&#x2F;www.w3.org&#x2F;Provider&#x2F;Style&#x2F;URI.html</a>