For some inane reason, Vim comes with a
ROT-13 feature. So, if you are ever
in need of rotating the letters of some portion of the file by 13, you can
do that with the simple g? binding.
For example, if you hit g?? on the following line:
Six dollar eggs
you will get
Fvk qbyyne rttf
As you can see, casing is preserved.
The only practical uses of this are Vimgolf and convincing people at coffee shops that you are a hacker.
See :h g? for more details.