Cycling order for `recenter-top-bottom'.
A list of elements with possible values `top', `middle', `bottom',
integer or float numbers that define the cycling order for
the command `recenter-top-bottom'.
Top and bottom destinations are `scroll-margin' lines from the true
window top and bottom. Middle redraws the frame and centers point
vertically within the window. Integer number moves current line to
the specified absolute window-line. Float number between 0.0 and 1.0
means the percentage of the screen space from the top. The default
cycling order is middle -> top -> bottom.