It looks like this is a project for nicer signed attestations. But it doesn't seem very opinionated about:

1. What is the attester (signer) attesting to, exactly?

This URL example is exactly this problem. And if you're really precise about it, they get less and less useful: "I attest that when I accessed this site at XYZ timestamp, it contained ABC content, and I saw ABC happen in person." or maybe alternatively to get away from the URL control, "I attest that these three non-malicious archives of this URL at this timestamp..."

And 2. Why should I trust the attester?