UPF1.0 Ch4 Power domains, name spaces, and precedence

4.1 Power domains
"In addition to creating the structural grouping of power domains, UPF commands create and connect new objects (switches, supply nets, etc.) that do not exist in the HDL, resulting in two orthogonal structures to the design, the power domain structure and the logic design structure."

"A power domain is a collection of design elements that share a primary power and ground supply net."

"A power domain can be either contiguous or non-contiguous. The power domain is contiguous if going from any object in the extent of the power domain to any other object in the extent does not require leaving that power domain. A power domain is non-contiguous if the extent of the domain needs to be left when connecting supply nets to design elements."