RE: C-x a C-x C-h

[Drew Adams]

> You're right, I tried it without having set mark. It wasn't 
> undefined here.

In fact, that's how I discovered that it ran `exchange-point-and-mark'. I too
got the error that mark was not set, turned on `debug-on-error', and saw that
`exchange-point-and-mark' was what was invoked.