Region

Given a domain, a region is a subset of the domain, and may be the entirety of the domain and may be empty (the null region). Regions are used to define conceptual areas, e.g. wells, or geologic media, or surface regions of a given land use type. Like domains, regions conceptually exist without the mesh. Once a region is resolved on the mesh, it is represented as a list of discrete entities of the mesh (either nodes, edges, faces, or cells).