Function layout 

pub fn layout(
    content: Rect,
    fields: usize,
    value_need: usize,
    list: ListShape,
) -> Layout

Lay out content for fields and a value needing value_need rows. Below WIDE the list sits above, taking what it needs; from WIDE side by side at full height, the value value_pane_width wide, fields in columns of list.min_col. By content, never focus, so Tab moves nothing.