Savaria Toyota Sienna Owner's Manual page 16

Where attachment to the wheelchair is not possible with the J-hooks,
the use of an optional webbing loop is acceptable if affixed by either
method to the wheelchair as shown in the diagram.
It is recommended that the front retractors are stored on the L-track rails
or oval pockets, and the rear retractors are anchored to the Slide 'N Click
fittings when not in use.
It is not recommended to store retractors in the rear storage bin or the spare tire
cover pocket.
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