What a FramePart draws.
public enum FramePartKind
Spec #33 viewer capability 2 (progressive zoom).
kind:method, kind:property, kind:ctor. Press Esc to clear.PaperA visible page's paper (opaque white): drawn first, so a page with no tile on the surface yet still shows, never a gap.ScaledA tile on the surface drawn at a zoom other than its own (stretched or shrunk): a placeholder, or a tile from before a zoom.SharpA tile on the surface at the frame's own zoom, drawn pixel for pixel.