Used to establish a reference frame for StrandOrientation if StrandDeform is true. The vector is expressed relative to the point cloud's local space.
The strand tangent defines the Y axis and this attribute represents the X axis in the point cloud's local coordinates.
If this attribute is not defined, the up-vector is calculated from the camera, which will make the deformations rotate if the camera moves.
If the size of this array does not match StrandPosition, it is ignored.
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