Comment by kazinator

Vi has "registers" and so do TeX and troff. I think once upon a time, it was more common to use the word for things beside CPU registers and I/O ports.

If a cons cell is a context with two registers (R) whose contents we can access (C), the only vestiges of that IBM machine are the A and D letters sandwiched in between to distinguish them.

Compared to how option letters change meaning between Unix commands, it's nothing. -h help? Nope, h)uman readable sizes.

^ to anchor regex at beginning; $ for end. Because on common keyboards, ^ is on the right, and $ on the left!