<Transmittal Root>
Every transmittal contains one <Transmittal Root> object
Every object in a transmittal is ultimately aggregated by the <Transmittal Root> object
A <Transmittal Root> organizes
- <Environment Root> instances that represent some environment
- <Library> objects that serve as repositories of representations of environmental objects that tend to be shared and reused
- metadata that applies to the entire transmittal