Why is Ronnie O'Sullivan playing in World Seniors Championship? Rule change explained

Ronnie O'Sullivan has reached the semi-finals of the World Seniors Snooker Championship in his debut appearance at the tournament. O'Sullivan's participation was made possible by a rule change that allowed him to compete, though the specific details of the rule alteration are not fully outlined in the excerpt. The seven-time world champion's strong run marks a notable debut in the seniors competition.