source_ property
Source names who asserted, as the caller gave it. This plane ranks no source above another, so it never outweighs a later Knowable.
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_;