ReadonlycountIndices (vertices) in the range, a multiple of 3; start need not be (see threeTriangleRanges).
ReadonlygeometryOptional ReadonlygroupsA folded multi-material mesh (multiMaterial: 'triangles'): its groups' ranges, one
after another in the mesh's triangles; start and count are then the
first group's start and the total. Absent for one range.
ReadonlystartFirst index (vertex, for non-indexed geometry) of the range, as three's drawRange.start and group.start.
Where one of BvhThreeScene.meshes came from.