ReadonlycountReadonlygroupThe group's position in geometry.groups, and its materialIndex.
ReadonlymaterialWhat material(object, info) gave its triangles (triangleMaterials), or undefined.
ReadonlymaterialReadonlystartFirst index (vertex) of the group's triangles, and how many indices, a multiple of 3.
One geometry group of a multi-material mesh (BvhThreeMeshSource.groups).