 A strength of the framework is that it addresses the fact that many of the “units” are unknown, and so, cannot simply be counted-up. Many species are still unknown to science; many features of species are undescribed. We may directly observe some objects (say, species) and want to quantify the relative number of un-observed units (say, features) that are represented by those objects. The relative number of units for any object or set of objects therefore has to be estimated through the use of an inferential model or a surrogate of some kind.