source_ property
Source is where the registration came from: "catalog" when it was enabled off the shelf, "org" when the org registered the URL itself. It is DERIVED from Listing rather than stored, because two columns for one fact is two chances to disagree.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? source_;