Changes:
- Added/edited documenting comments.
- Fixed wrong parameter name: renamed ignoreSelectedBox to includeSelectedBox (in Page.Overlaps())
- Disabled unused method (Page.PartCount).
- Removed unnecessary 'ref' keyword (in 'ref parts' parameter of the various 'AppendParts' methods).
- Avoid similar names to different objects:
- Renamed the (private) 'box' to '_mesh' in ClippingD3D.
- Renamed the (private) 'lines' to '_clippings' in PlayerViewD3D.