public override IGreenJsonSymbol VisitUnknownSymbolSyntax(JsonUnknownSymbolSyntax node, _void arg) => node.Green;
public override Style VisitUnknownSymbolSyntax(JsonUnknownSymbolSyntax node, SyntaxEditor <TSyntaxTree, IJsonSymbol, JsonErrorInfo> syntaxEditor) => syntaxEditor.Styles[unknownSymbolStyleIndex];