Shifu Shi Yan Xiu is a master practitioner in the technique of Chin Na, which controls or locks an opponent's joints or muscles/tendons so that they cannot move, thus neutralising the opponent's fighting ability.
Chin means to seize or trap, na means to lock or break, and while those actions are very often executed in that order (trap then lock), the two actions can also be performed distinctly in training and self defense. Which is to say, a trap isn't always followed by a lock or break, and a lock or break is not necessarily set up by a trap. There is quite a bit of overlap between chin na theory and technique with the branches of traditional Chinese medicine known as Tui Na as well as the use of offensive and defensive qigong as an adjunct of chin na training in some styles.
The recent understanding that grappling is as important as striking has also caused some Chinese martial arts instructors to focus on their chin na techniques, even expanding the system by incorporating or developing new ones. This is one reason why the chin na of one school may differ from that of another.