That is the safety catch that holds the top half up in case the lift system settles or fails. When you raise the top you should hear the catch drop into place when the top reaches the full up position. Only when you lower the top do you need to pull on the loop to release the catch. Sometimes to get it to release you may want to press the up button to take some weight off the catch. If you don't use it the top won't go down.
I know, you already knew all of that, you just wanted to see if anyone else did.
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