Google does cache results, and could via comparison with cache notice changes, and claim, the page was updated sometime between. I've always wondered, how sear

Google does cache results, and could via comparison with cache notice changes, and claim, the page was updated sometime between. I've always wondered, how search engines get a hold of timestamps. Locally with a cached sample, like I explained above, parsing a page's content or some metadata? It's not like the HTTP protocol sends me a "file created/last modified date" along with the payload, does it?