In advance, I'm sorry if this topic has already been covered. Also, I apologise if this forum topic should be in a different category. If possible, I will change it to the appropriate one.
There is a hidden "Content" button on (probably) every page of e621 and e921. It is just an <a> tag with no id or class, but it has a special style format and an actual link. Every time the page loads, the link seems to be different, specifically the id it uses. It links to /cdn-cgi/content that accepts an "id" parameter. The page itself is filled with completely unrelated text like "Semiconductor Engineering: A World of Wonders" or "Cable Television: A Journey Through the Realm of Coaxial Cables". It seems that it doesn't have anything hidden or something like that, just heading and paragraph tags. Also, I don't know how long this hidden link has been here. This is how this hidden line of code looks on e621:
<a href="https://e621.net/cdn-cgi/content?id=<some_kind_of_id>" aria-hidden="true" rel="nofollow noopener" style="display: none !important; visibility: hidden !important">Content</a>
Is this some kind of easter egg, or am I missing something?