This was inserted some time ago (a few months at least) to allow Sabre to autoprice xONEx itineraries. It is in APTCO language. The rules are generated by a computer, for another computer to read. They are not intended to be human readable.

The xONEx product allows the start and end cities to differ. This is only allowed domestically and between certain countries. But all the fares are published as XXX-XXX (i.e., back to the same city). So to get around that, formally speaking you have a surface sector at the end of your itinerary joining the finally visited city with the fare destination. This is called a “fare break surface sector” because it occurs at a fare break point. Fare break surface sectors are usually disallowed because they increase the complexity of itinerary pricing so much if you have to consider fares for non-visited cities as part of your pricing calculation. Nonetheless, they are required here.

The xONEx product also has very unusual transfer allowances (a certain number in each continent, you can go through the same city multiple times but only fly the same pair of cities once in the same direction): again, because it is unusual, there is no short cut in the ATPCO language, it all has to be expressed explicitly.

So that’s why it’s so long and incomprehensible.

I have no doubt it is full of exploitable mistakes, if someone looks carefully enough.