> Facebook, like many sites, uses versioned URLs - these URLs are never updated to have different content and instead the site changes the subresource URL itsel

> 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... Why not use the ETag header instead? https://www.w3.org/Provider/Style/URI.html https://www.w3.org/Provider/Style/URI.html