Function boundary_surface 

pub fn boundary_surface(
    part: &NamedModel,
    namer: &Namer,
    edges: &[Chain<NurbCurve3D>],
    tangent: &[&str],
) -> GeopResult<SheetSpec>

The sheet spanned between edges, tangent along tangent (see the module docs), each a curve picked, the edges of tangent by name, in part: what to build, named after namer, as BoundarySurface says.