Inline related resources on a single RequirementDefinition read. Supported value is DataSource — the backing configuration resource that dataSourceId addresses, returned in place of a dataSourceType a caller would otherwise have to derive a collection from. Unsupported values return 422 instead of being silently ignored. Expansions are not available on list/search rows.

Requesting DataSource is never an error: the key is simply omitted when there is nothing to inline — a requirement type that has no configuration, a null dataSourceId, or a configuration resource not yet addressable on V3. A supported value that resolves nothing is a 200 with the key absent; only an unsupported value is a 422.