yjs/yjs on GitHub

The og adapter reads a page's Open Graph tags and renders the card the author of that page wrote for it — title, description, image.

It is the bookmark case: a link you want to show as a card rather than as a row. Elsewhere holds the same repository as a plain link; this is what the other treatment looks like, and the reason both page types exist.

It only sees what the server sends

The tags are read from the HTML as fetched, with nothing executed. A page that assembles its own head in the browser has no Open Graph tags as far as this adapter is concerned, and the card falls back to the hostname — which is exactly what the first URL tried here did.