 Complete the following phrase:  The Pro14, originally known as the Celtic League and later as Pro12, adopted a four-team playoff starting with the 200910 season. The format was essentially identical to that of the English Premiership. Through the 201314 season, the final was held at a ground chosen by the top surviving seed, with the caveat that the venue must have a capacity of at least 18,000. In 201213, top seed Ulster could not use its regular home ground of Ravenhill for that reason the ground was later expanded to meet the requirement. The league changed to using a predetermined site for its championship final in 