[throw0101a]

> I thought the ASCII upper-case <-> lower-case being a bit operation as being clever.

From "Things Every Hacker Once Knew" (2017), has an entire section on ASCII and the clever bit-fiddling that occurs:

* http://www.catb.org/~esr/faqs/things-every-hacker-once-knew/...

* Discussion from ~2 months ago: https://news.ycombinator.com/item?id=37701117