Question: What did the IWF rules discuss in reference to the knees and elbows of athletes?
About the article "Olympic weightlifting", section "History".

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WVR's rules differ somewhat from the unified rules of mixed martial arts.
Among the differences are the allowance of knees and stomps to the head of downed opponent while elbows to the head and soccer kicks are prohibited.
Similar to the Unified Rules, fights have 3 rounds each lasting 5 minutes. 
Competition among people concerning who can lift the heaviest weight has been recorded in diverse and ancient civilizations as early as the earliest known recordings of such human events, including those found in Egypt, China and in ancient Greece.
Today, the modern sport of weightlifting traces its origins to the European competitions of the 19th century.
The first male world champion was crowned in 1891.
Women's competition did not exist, and the weightlifters were not categorised by height or weight.
The first Olympic Games of 1896 included weightlifting in the Field event of the predecessor to today's Track and Field or Athletics event.
During the 1900 Olympic Games, there was no weightlifting event.
Weightlifting resumed as an event, again in Athletics, in 1904 but was omitted from the Games of 1908 and 1912.
These were the last Games until after the First World War.
In these early Games, a distinction was drawn between lifting with 'one hand' only and lifting with 'two hands'.
The winner of the 'one hand' competition in 1896 was Launceston Elliot, while the winner of the 'two hands' event was Viggo Jensen of Denmark.
In 1920, weightlifting returned to the Olympics and, for the first time, as an event in its own right.
At these Games, which took place in Antwerp, Belgium, fourteen nations competed.
The competition lifts were the 'one hand' snatch, the 'one hand' clean and jerk and the 'two hands' clean and jerk.
At the next Olympic Games, in Paris, France, in 1924, the 'two hands' press and the 'two hands' snatch were added to the programme, making a total of five lifts.
In the Olympic Games after 1920, instead of requiring all competitors to compete against each other regardless of size, weight classes were introduced and, by the 1932 Olympic Games, weightlifting was divided into five weight divisions.
In 1928, the sport dropped the 'one hand' exercises altogether leaving only the three remaining exercises: the clean and press, the snatch and the clean and jerk.
By 1972, the clean and press was discontinued because athletes started to push with legs and bend backwards instead of strictly pressing the weight overhead, and this left the sole elements of what is today's modern Olympic weightlifting programme – the snatch and the clean and jerk.
The snatch entails pulling with a very wide grip the barbell overhead without pressing out with the arms.
It is a very precise lift that can be nullified by a lack of balance of the athlete.
The clean and jerk is more forgiving using a narrower grip pull the bar to the shoulders and then using the strength of the legs push until arms reach full extension without a press out.
A competition for women was introduced at the 2000 Olympic Games in Sydney, Australia.
As early as 1987, there were official world championships awarded to women weightlifters such as Karyn Marshall and Judy Glenney.
In 2011 the International Weightlifting Federation ruled that athletes could wear a full-body "unitard" under the customary weightlifting uniform.
Kulsoom Abdullah became the first woman to do so at the U.S. National Championships that year, and athletes are allowed to do so at the Olympics.
IWF rules previously stated that an athlete's knees and elbows must be visible so officials can determine if a lift is correctly executed.
Slamm MMA fights were conducted under different rules from the North American Unified Rules.
Among the differences were the allowance of knees and stomps to the head of downed opponent.
However elbows to the head and soccer kicks were prohibited.
Muay Thai fights were conducted under full muay thai rules with elbows 5 X 3 rounds. 
The Art of War Fighting Championship tournaments are conducted according to the Art of War Unified Rules System, which allows for a variety of striking and submission techniques including soccer kicks, stomps, elbows, and knees to a grounded opponent. 
RESPECT.FC's rules differ somewhat from the North American Unified Rules.
Among the differences are the allowance of knees to the head of downed opponent and stomp kicks to the body, while elbows to the head of downed opponent and soccer kicks are prohibited.
Similar to the Unified Rules, fights have 3 rounds each lasting 5 minutes.
Title Fights are 5 rounds.