direction property
Direction is out, in or both. Out follows an edge from its entity to its value — what the node points at; in follows it the other way — what points at the node; both is the union of the two, not a third rule. Absent is out.
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? direction;