Root
The root concept refers to the container of domains. Domains are the top level definition in RIDDL but because RIDDL is hierarchical, and you can have more than one domain definition at the top level, something has to contain those top level domains. We call that the root. A root is not a definition since it has no name. You can think of a root as the file in which a domain is defined.
At the file root of the first file riddlc
reads.