Both frames render identically — that's the goal. The win is in the bytes and requests below, not the look. They're served live by mod_pagespeed 1.15 on demo-httpd-1.1.modpagespeed.com; the optimized frame applies only this filter. Right after a cache purge it may briefly match the original while the worker rewrites it — reload to see the result.

This optimization works at the HTTP response-header or document-head hint level, so it leaves no change in the page body to diff — see it live in the frames above (or in the response headers).