I could not find a good picture of the exercise, but you can see the twist of the chest in this picture. The head and hips stay facing/looking forward, while the chest/shoulders and outstretched arms twist as a unit to their fullest (straight to the front/back (90 degrees) or even a bit more, if everything else can be kept without breaking position).
The basic exercise is done with feet shoulder width (or a bit more) apart. Stand tall and reach out to the sides, stretching everything, and alternatively rotating the torso left and right,pausing at the farthest point on each side to stretch/contract/reach for 10 seconds, while lifting your sternum to tilt your head and (straight) neck backwards.
As you rotate the torso, the outstretched arms just move with it, with no additional movement in the shoulder joint. So while the arms start stretched out to your sides, after your torso turns 90 degrees, they are reaching for the other set of walls in the room. Although the head stays facing forward, it requires an effort like turning the head maximally to keep it there, as the torso rotates the other way (isometrically contracting and stretching the cervical spine).
You can also see in this picture (especially the woman), how when the thoracic spine is fully extended (arced backward, sternum lifted), the head goes backward, even though the neck itself is totally straight. We seldom make that full extension in daily life, but it is the counter to the all too common forward slump over the desk, computer or cell phone.
What is hard to see in this picture, is that the man maintains a high degree of external rotation of his arms (humerus) in the shoulder joints, even though his left hand (wrist) might be decoratively rotated inward (palm down), and his right arm is rotated internally to a high degree at the elbow. It is clear to see that his shoulders/shoulder blades are dropped rock bottom - no hunching up.
Ballroom dance changed a lot over the 20th century, becoming more athletic. Very full range of motion is central to their athleticism - kind of the best practice for that characteristic.
Full extension of everything at once - head to foot standing to tall, stretching each vertebrae open, and reaching strongly with each hand in opposite directions - and then putting maximal twist on the shoulder joints (external rotation of the arms and lowering of the shoulder blades) as well as the spine (like wringing water out of a towel); prevents the next joint in the chain of motion from contorting, to provide slack for the one we are trying to stretch, when isolated stretches are used (e.g. rounding your back over when stretching hamstrings. The whole "kinetic chain" is exercised and stretched, from head to foot, and from hand to hand.
This kind of stretch requires no jerky sudden accelerations, or external weights that might exceed the ability of the weak point in the motion. Full control. You can easily control the amount of contraction through any injured or sticking point, depending on how it feels that day.
The squeeze or reach (isometric contraction) at the end of the movement preferentially strengthens the muscles at that extreme point of the range - optimally targeting the development where strength is needed to improve the range of motion. As they say in Chinese internal martial arts, "add one inch (to your max reach), double the power".
Safe and effective rehab.