Available for compounds to store the velocities of the shapes at the StrandPosition values.
This attribute is set and used by the Create Strands and Generate Strand Trails compounds.
This attribute is not updated by the Simulate Particles or Simulate Rigid Bodies nodes.
If this attribute exists, it is used for rendering motion blur. If this attribute is not defined, the base particle's PointVelocity is used instead.
If the size of this array does not match StrandPosition, it is ignored.
