The All Dimensions Wiki is a wiki powered by Fandom that describes mostly fictitious(?) cosmology, geometry, and other dimension-related things. Despite normally being one of the smallest entities, it contains everything on the wiki because it is the wiki.
The AD wiki contains everything on it, so why does it have a container? Technically, at any given point in time, the AD wiki is contained by something, this thing normally being inside a universe in the form of a computer screen. However, the AD wiki contains a universe along with many, many other things (including itself) as well, causing an infinite loop of containment vaguely similar to the endless self-containment of The Box. This would make it so that there is no truly dominant thing in any hierarchy because that hierarchy would repeat itself to no end.
It can be said that the wiki does not contain an actual universe, but merely contains a page detailing that universe. Little do those who believe this know, they could be just another instance of something from one of the pages on a higher AD wiki, a similar theory to the simulation hypothesis.
Any page on the wiki that would claim to contain the AD wiki wouldn't be right, but also may not necessarily be wrong. By writing a page on the wiki, you have, of course, placed it inside of the AD wiki, another property similar to that of The Box's. However, the thing described on that page could indeed contain the AD wiki; for example if a page about a laptop were to be made then that would contain the AD wiki.
Despite literally being the wiki, it is not the dominant thing on the wiki because the wiki can't logically surpass itself. Along with that, it is neither the smallest nor largest entity (normally).