This isn't really an easter egg, just more of a mild bug that makes you think - hopefully a little more about your own applications.
If you type in "0" in the page navigation bar, it takes you to the typical global page / page zero for desktop.
In the component view, instead of displaying page processing and shared components, it displays application level components - items, process, computations; and an "About" region in the third column, above recently edited pages. Useful stuff...
If you type "-0", it renders page zero detail as if it were a normal page.
If you type "-1", or any other negative number,
- in 4.2.1 it takes you into a horrible "no data found" that's annoying to recover from, similar to if you type a positive page number that doesn't exist
- in 4.2.2 it handles it a little more elegantly, a little better than it did pre 4.2 - displaying no page detail.