What domain will be the forest root domain in a multiple-domain installation with a single forest?

In a multiple-domain installation with a single forest, the forest root domain is typically the first domain created during the forest setup. It acts as the primary domain that holds the schema and configuration partitions, serving as the foundation for all other domains within the forest. This root domain is often given a unique name, such as "root.local," and is crucial for managing trust relationships and policies across the other domains.