That's the OLD rules. The new rules state segments of 4 allowed in each continent except for North America which is 6. You may stop at each segment. You may purchase additional segments within each continent for US$550 for First Class, US$400 for Business and US$150 for economy.

So let's just say you're flying from NY to LON. From there, you are allowed 4 segments to your next intercontinental departure point. So from LON-PAR-MAD-HEL-FRA then to BKK. In fact, that's 5 stopovers within Europe then.

If you open jaw, meaning fly into one city and surface, even though you have no flight in between, that is still considered a segment irrespective if any oneworld flight occurs.