1. One or more computer-readable media having computer-readable instructions therein that, when executed by a computing device, cause the computing device to perform acts comprising: receiving a machine-readable set of one or more constraints for an Open Packaging Convention (OPC) package; receiving a package following the OPC; and determining, without user interaction and for parts of the package reachable by a chain of relationships, that the parts and their relationships are valid or invalid according to the set of constraints.