BlockRestrictable Interface
The BlockRestrictable interface is inherited by every object in MOOSE that supports running on a subset of the mesh domain corresponding to a subdomain. This interface provides a validParameters function that also supports a uniform way of handing reading in subdomain restrictions. Specifically, every object may be restricted to one or more subdomains simultaneously. Subdomains 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 subdomains that an object is restricted to when no restrictions are supplied.