cua-scroll-down is an interactive compiled Lisp function in `cua-base.el'.

(cua-scroll-down &optional ARG)

Scroll text of current window downward ARG lines; or near full screen if no ARG.
If window cannot be scrolled further, move cursor to top line instead.
A near full screen is `next-screen-context-lines' less than a full screen.
Negative ARG means scroll upward.
If ARG is the atom `-', scroll upward by nearly full screen.