This figure illustrates the precedence rules used in CGNS. It shows multiple levels in a CGNS file hierarchy, each with a ReferenceState_t node.

At the highest level, as a child of the CGNSBase_t node, the ReferenceState_t node provides the global default reference state. At the next lower level, below a Zone_t node, it provides a new default for that particular zone, overriding the global default. Next, below a ZoneBC_t node, it provides a new default reference state applicable to the boundary conditions in the zone, overriding both the global and zonal defaults. At a still lower level, below a BC_t node, it provides a new default reference state for a specific boundary condition, overriding all three higher-level defaults.