Rail Shape
Indicates the shape of a minecart rail this property is applied to represents.
Minecart rails can be in one of three layouts:
Straight flat, which will keep the Minecart on the same Y level and direction of travel. These rails can either be north to south or east to west.
Straight ascending, which will ascend the Minecart up by one Y level, and maintain the same direction of travel.
Corner, which will change the Minecart's orientation by 90 degrees, either clockwise or anticlockwise, depending on the direction change.