The distance fraction in the horizontal direction.
A value of -1.0 corresponds to the edge on the "start" side, which is the left side in TextDirection.ltr contexts and the right side in TextDirection.rtl contexts. A value of 1.0 corresponds to the opposite edge, the "end" side. Values are not limited to that range; values less than -1.0 represent positions beyond the start edge, and values greater than 1.0 represent positions beyond the end edge.
This value is normalized into an Alignment.x value by the resolve method.
final double start;