This is not a part of ruststep. These EXPRESS schemas are included in this git repository in order to test our EXPRESS compiler.
Copied from http://www.steptools.com/stds/archive/ with minor modification. It says
ISO standards are copyrighted, but the EXPRESS schemas can be distributed without restrictions. The full standard document is needed to understand semantics and usage of a schema. Documents can be purchased through the ISO Central Secretariat or national standards bodies.