The current format sees the eight group winners and eight runners-up qualify to the Round of 16, in which group winners play host to the runners-up in two-legged series, matched regionally, with away goals, extra time, and penalties used as tie-breakers. The regional restriction continues all the way until the final, although clubs from the same country cannot face each other in the quarterfinals unless that country has three or more representatives in the quarterfinals. Since 2013, the final has also been held as a two-legged series, on a home and away basis.