Question: What highly refined skill set is seldom used in in Classical dressage?
About the article "Equestrianism", section "Haute École".

Candidate passages:
The "haute école" (F. "high school"), an advanced component of Classical dressage, is a highly refined set of skills seldom used in competition but often seen in demonstration performances.
Leading haute ecole demonstration teams include:
 The Cadre Noir in Saumur, France.
 The Spanish Riding School in Vienna, Austria.
 The Escola Portuguesa de Arte Equestre in Queluz, Portugal.
Royal Andalusian School of Equestrian Art in Jerez de la Frontera, Spain.
South African Lipizzaners of Midrand in South Africa.
British Dressage is the organisation which oversees all affiliated dressage competitions and training in the United Kingdom.
British Dressage is a member of the British Equestrian Federation.
In addition to the usual dressage competitions, British Dressage also oversees the British Young Riders Dressage Squad (BYRDS) and all para-equestrian dressage. 
Tuttle originally trained and practiced as a lawyer in Boston, but in 1927 joined the US Army as a commissioned officer.
Between 1930 and his retirement as a Colonel in 1944, he held at post in Fort Riley, Kansas at the Cavalry School.
Tuttle's equestrian skills were largely self-taught, and he became the top dressage rider in the US before the majority of the country even knew such a sport existed.
Army historian Louis DiMarco says, "Tuttle did so much with so little and was so little appreciated.
He was the only officer to focus strictly on dressage.
Everybody else in the Army world...who did dressage learned what to do and how to do it from him.
"Tuttle owned and trained his own horses, partially so that the horses could focus strictly on dressage and not be used for other sports or cavalry exercises; this was unusual for the times.
He was set apart from many of the Olympic riders of the time by being older, not a West Point graduate, a quartermaster officer, and riding in dressage when few other officers appreciated the formality and discipline of the sport.
He trained many of the military dressage riders who followed in his footsteps, including Major Robert Borg who competed in dressage at the 1948 and 1952 Summer Games.
After his retirement, Tuttle continued to ride and train, and never sold his Olympic mounts.
He is buried along with three of his horses (Vast, Si Murray and Olympic) at the Fort Riley cemetery.
In 2002, Tuttle was inducted into the United States Dressage Federation Hall of Fame in "recognition of his seminal contributions as a Cavalry officer to the development of dressage in the U.S." 
 vs. competitive dressage.
Modern dressage evolved from the classical school, although it now exists in a somewhat different form from its ancestor.
Competitive dressage is an international sport ranging from beginner levels to the Olympics.
Unlike classical dressage, competitive dressage does not require the airs above ground, which most horses cannot perform well even with correct training, due to physical limitations.
Instead, competitive dressage focuses on movements such as the piaffe, passage, half-pass, extended trot, pirouette, and tempi changes.
In theory, competitive dressage should follow the same principles as classical dressage.
However, there has been criticism by some riders for the trend at all levels for "quick fixes" and incorrect training that makes the horse "appear" correct, but that is in fact neglecting the fundamentals.
Classical riders criticize such training methods on the grounds that they are biomechanically incompatible with correct movement, are painful to the horse, and cause long-term physical damage.
These short-cuts usually catch up to the rider as they move up the levels and need to be corrected to perform certain movements.
While these modern methods, such as the highly controversial rollkur technique, can produce winning animals, classical dressage riders argue that such training is incorrect and even abusive.
It is also believed by some that competitive dressage does not always reward the most correctly trained horse and rider, especially at the lower levels.
For example, some riders who consider themselves to be training classically would not ask their horse to hold his head near-vertical when he first began training, and this would be penalized at the lower levels of competitive dressage, marked down because the horse is not considered to be correctly on the bit.
Other riders, who also would consider themselves classically trained, would disagree, saying that if a horse is not ready to travel in a correct outline ("on the bit") he is not ready for competition, and this is the reason such horses would be marked down.
The highest form of classical riding, as well as dressage, High School dressage, of Haute Ecole, takes years for both the horse and rider to master.
When a horse is advanced in its training, it can perform not only Grand Prix dressage movements such as collected and extended gaits, passage and piaffe, but some can also perform certain "Airs Above the Ground," although usually a horse will only be trained in one air, and only if it is particularly able. 
The piaffe is a dressage movement where the horse is in a highly collected and cadenced trot, in place or nearly in place.
The center of gravity of the horse should be more towards the hind end, with the hindquarters slightly lowered and great bending of the joints in the hind legs.
The front end of the horse is highly mobile, free, and light, with great flexion in the joints of the front legs, and the horse remains light in the hand.
The horse should retain a clear and even rhythm, show great impulsion, and ideally should have a moment of suspension between the foot falls.
As in all dressage, the horse should perform in a calm manner and remain on the bit with a round back.
The piaffe was originally used in battle to keep the horse focused, warm, and moving, ready to move forward into battle.
In modern times, the piaffe is mostly taught as an upper level movement in Classical dressage and as a Grand Prix level movement.
Additionally, it is needed to develop the levade and from that, the airs above the ground.