Looking at it again, I think the comment about Roll on the engine is incorrect in my opinion.
The comment is written as follows.
Rotation around the forward axis (around X axis), Tilting your head, (0=Straight, +Clockwise, -CCW)
I think the correct comment should be as follows.
Rotation around the forward axis (around X axis), Tilting your head, (0=Straight, +CCW, -Clockwise)
The reason I think this way is because Rotator treats Roll as a right-handed system as it is written in here.
Rotator treats yaw as left-handed but pitch and roll as right-handed.
And in a right-handed system, positive rotation is counterclockwise about the axis of rotation.
Please see Left- vs. Right-Handed Coordinate Systems .