Recommended 

fy: 

The button should appear in the lower left-hand corner of the window or dialog box for expansion in the vertical direction and in the lower-right hand corner for expansion in the horizontal direction. 

Required 

fz: 

If the window or dialog box contains a scrolling list positioned to the far right side of the pane, do not align the drawn button with the scroll bar. For example, the button should be aligned with the list, not the scroll bar.