we have to collect all Content-ID's which are rendered in the current request in a performant way. Is it possible to hook into an existing event that is triggered when content is rendered? If not, we have already a custom ContentAreaRenderer, so we can add logic there for all content that was added to a ContentArea. But we don't get a complete list of Content-ID's there because it's possible that blocks have ContentReference-properties(for example Images) that will be rendered too. It's also possible that content is added to XHtml properties, so we need to add that logic there as well. How can we collect a complete list of rendered Content-ID's?
Out of interest, why do you need to collect all the content id's when the page is rendered?