Function shell 

pub fn shell(
    part: &mut NamedModel,
    namer: &Namer,
    solid: SolidId,
    open: &[FaceId],
    thickness: Scalar,
    thicker: &[(FaceId, Scalar)],
) -> GeopResult<SolidId>

Hollows the solid solid of part out to walls thickness thick — measured inward from its faces, or outward for a negative thickness — those of the faces in thicker as thick as it says instead — open where its faces open were — see the module docs — and returns the hollowed solid, which replaces it and is named namer’s root.

What stays of the solid keeps its names. What is new is named after what it was made from, with Scalar the operation:

• shell(Scalar,X): the inner copy of the face, edge or vertex X kept; for a face X taken away, the rim it leaves — shell(Scalar,X,0), shell(Scalar,X,1), … if that is several faces;
• shell(Scalar,E,start) / shell(Scalar,E,end): what is left of an edge E between two faces taken away, at its start and its end.