What is the difference between a hole feature and a void feature?
A hole is a variant of a void feature, and the difference between a void and a hole is only apparent when one triangulation is merged into another. Consider merging surface B into surface A when part of surface A is replaced by surface B. If surface B has voids, then the surface B voids will become part of the merged surface. If surface B has holes, then the merged surface will contain areas of surface A that correspond to the surface B holes.