| http://www.w3.org/ns/prov#value | - In an example embodiment, the adjustable tightening unit 180 may be provided to enable a cord 190, string, cable or other flexible line to be threaded through a channel in a distal end of the anterior interface region 150 so that the anterior interface region 150 may be drawn toward the frame portion 20 between the clips 170 by tightening the cord 190 via the adjustable tightening unit 180.
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