The Bounding Box Vector handle is a directed arrow radiating from an
origin.  This is used to interactively choose a direction.  The
Bounding Box Vector differs from a normal Vector handle in the
addition of a few extra controls in the RMB menu to snap to the
bounding box of the input.

Parameters:

    input       - A group field.  The centroid of this group is used
                  as the default origin.
    onoff       - Whether the handle is enabled, 1 means enable.
    scale       - A global scale defined by the handle.  This is
                  defined by dragging the red tip of the handle arrow.
    twist       - The amount to twist around the given direction.
                  This is controlled by dragging the circle at the end
                  of the arrow.  It gives the total twist in degrees.
    tx, ty, tz  - The origin of the arrow.
    vx, vy, vz  - The normalized direction in which the arrow points.

See Also: Angle, Vector
