positionPriority property
EdgeLabelPositionPriority.horizontal means to stick label to horizontal line inside edge path if possible. EdgeLabelPositionPriority.vertical means to stick label to vertical line inside edge path if possible. EdgeLabelPositionPriority.none default value, means to stick label to vertical line if graph's orientation is MatrixOrientation.Horizontal and to horizontal line of graph's orientation is MatrixOrientation.Vertical.
Implementation
final EdgeLabelPositionPriority positionPriority;