A beautiful precision job and a snazzy detail by Ray Joyce.
The idea is to incorporate a bungee into the Dyneema ‘limiter’ strop for the automatic speed/height ‘moding’ adjustment on the swing rigs.

A lesser mortal would have tied the bungee separately, but this would have left an untidy loop of Dyneema when the limiter was slack.
Here is Ray’s description of the procedure:

I did a few trails and decided not to include tying the elastic within the fixing knots because of it being too bulky. I found that with a piece of elastic captive within the 
spectra it did not need much encouragement to stay where it was, so came up with a solution which seems ok.

The pics show.

You'll see that at each end I passed the elastic in/out/in then through the 
spectra for 50mm then out/in/out. I then whipped each end over the end 4mm sections.