Function append 

pub fn append(
    scene: &mut Scene,
    other: &Scene,
    parts: Option<&SectionParts>,
    transform: Option<Affine>,
)

Append other, whose parts were recorded as parts (record), so that a tracked scene keeps them: each becomes a part of scene at the same place, its bounds carried through transform. Without parts everything other draws belongs to whatever part this append is in.