BoundaryRestrictable Interface
The BoundaryRestrictable interface is inherited by every object in MOOSE that supports running on a subset of the mesh domain corresponding to a boundary. This interface provides a validParameters function that also supports a uniform way of handing reading in boundary restrictions. Specifically, every object may be restricted to one or more boundaries simultaneously. Boundaries may be specified either as numeric IDs or strings (when supported by the Mesh format or named entities are used). Finally, this interface handles queries about the set of boundaries that an object is restricted to when no restrictions are supplied.