scroll-downscroll-down is an interactive built-in function in `
C source code'. (scroll-down &optional ARG) Scroll text of selected window down ARG lines. If ARG is omitted or nil, scroll down by a near full screen. 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. When calling from a program, supply as argument a number, nil, or `-'.