RE: add non-chord keys to repeat isearch

[Drew Adams]

> I have no idea what the "next" and "prior" keys mean. Could you please
> explain? Thanks.

They are the (pseudo-function) keys that are typically labeled `Page Down' and
`Page Up'. (They are often next to the keys labeled `Home' and `End'.)

Their Emacs names are often written `<next>' and `<prior>'. (I tend to drop the
angle brackets.) When binding, they are written [next] and [prior].