Question: What is the function of clipless pedals for cyclists?
About the article "Cycling", section "Equipment".

Candidate passages:
Clipless pedals (also clip-in or step-in) require a special cycling shoe with a cleat fitted to the sole, which locks into a mechanism in the pedal and thus holds the shoe firmly to the pedal.
Most clipless pedals lock onto the cleat when stepped on firmly and unlock when the heel is twisted outward, although in some cases the locking mechanism is built into the cleat instead of the pedal.
Clipless refers to the toe clip (cage) having been replaced by a locking mechanism and not to platform pedals which would normally not have toe clips.
The clipless pedal was invented by Charles Hanson in 1895.
It allowed the rider to twist the shoe to lock and unlock and had rotational float (the freedom to rotate the shoe slightly to prevent joint strain).
The M71 was a clipless pedal designed by Cino Cinelli and produced by his company in 1971.
It used a plastic shoe cleat which slid into grooves in the pedal and locked in place with a small lever located on the back side of the pedal body.
To release the shoe a rider had to reach down and operate the lever, similar to the way a racing cyclist had to reach down and loosen the toestrap.
The lever was placed on the outside edge of the pedal so that in the event of a fall the lever hitting the ground would release the foot.
The pedal was designed for racing, in particular track racing, and because of the need to reach them to unclip they have been referred to as "death cleats".
In 1984, the French company LOOK applied downhill snow skiing binding or cleat technology to pedals producing the first widely used clipless pedals.
Initially used by triathletes in order to facilitate faster "transitions", Bernard Hinault's victory in Tour de France in 1985 then helped secure the acceptance of quick-release clipless pedal systems by cyclists.
Those pedals, and compatible models by other manufacturers, remain in widespread use today.
The cleat is engaged by simply pushing down and forward on the pedal, or, with some designs, by twisting the cleat in sideways.
Then, instead of loosening a toestrap or pulling a lever, the cyclist releases a foot from the pedal by twisting the heel outward.
The next major development in clipless pedals was Shimano's SPD (Shimano Pedaling Dynamics) pedal system.
Whereas Look cleats are large and protrude from the sole of the shoe, SPD cleats are small and could be fitted in a recess in the sole, making it possible to walk (although comfort will vary, as the soles of different cycling shoes vary in their rigidity depending on design).
Cycling shoes have rigid soles to maximize power transfer and efficiency.
They may be specific to road or mountain biking, or usable for both.
Shoes designed for mountain biking typically have recessed cleats that do not protrude beyond the sole of the shoe, and have treads for walking on trails, as walking or carrying the bike is often required.
Road cycling shoes are typically lighter than their mountain bike counterparts, and feature a protruding cleat and less weather proofing.
The protruding cleat makes these shoes impractical for walking, as doing so can damage the cleat.
Mountain bike cleats can generally be mounted without difficulty to road shoes although sometimes an adapter is required.
Such attachment is not usually possible for road pedals, as the cleats are normally too large to be mounted on mountain shoes.
The smaller mountain bike cleats are attached to the sole of the shoe by two bolts; larger road-specific cleats are attached by three.
Various manufacturers have produced their own designs of clipless pedal systems over the years, most notably BeBop, Campagnolo, Coombe, Crank Brothers, LOOK, Shimano, Speedplay, and Time. 
Shimano Pedaling Dynamics, also known as SPD system is a design of clipless bicycle pedals.
The SPD pedal was released by Shimano in 1990.
While not the first, its innovation was its small cleat which fitted in a recess in the sole of a shoe designed for SPD use.
The shoe could be also used for walking whereas previous systems (other than the Cyclebinding system) had a large protruding cleat.
Clipless pedals use a system of cleat retention which is quite similar to that of a downhill ski binding.
Generally, clipless pedals are seen to be safer than the older style of pedal/shoe integration using toeclips, toestraps and shoeplates due to ease of disengagement.
There is a small allen key adjustment for the strength of heel twist to release, so beginners can have it 'soft' and easy to get out, and then tighten it up as they progress. 
In previous years, cyclists tied their shoes to their pedals with toe-clips, allowing them to not only push the pedals down but also pull them up.
In 1985, Hinault had used clip-ins (clipless pedals), which allowed the shoes to snap into the pedal.
His victory in this Tour made these clip-ins popular.
There was some criticism that the time trials were too important.
If the time trials would have not counted towards the general classification, the result would have been as follows:The total length of the time trials reduced from in 1985 to in 1986.
Tour director Levitan felt after the 1985 Tour de France that the race had been too easy, and made the course in 1986 extra difficult, including more mountain climbs than before.
After every stage, around four cyclists had been selected for the doping controls.
None of these cyclists tested positive for doping. 
Bicycle Pedal Platform Adapters are adapters designed to temporarily convert clipless bicycle pedals, commonly used in mountain biking, into more traditional platform pedals which have a larger and flatter area for the foot to rest on.
There are several advantages to using clipless cycling pedals over flat ones, especially in mountain biking and racing.
They keep the foot from slipping in wet and muddy conditions and provide better transfer of power.
To be able to use these pedals you also need to wear special cycling shoes.
Since the pedal platform adapters temporarily converts these into platform pedals, this allows you wear your normal shoes without switching to another bike with a different pedal setup.
They can be fastened by using bolts but as their major strength is their temporary use, it is also common for them to be mounted using different snap-on techniques. 
Reflectors and reflective tape provide additional visibility (especially when applied to moving parts of the bicycle) and are mandatory in many jurisdictions.
Pedal reflectors in particular are very visible to following traffic as they move up and down; unfortunately they are not compatible with most clipless pedal systems, although adaptors are available for some, mainly older SPD models, and a few single-sided designs are available with built-in reflectors.
In the UK, where front and rear pedal reflectors are compulsory after dark, most cyclists with clipless pedals are therefore riding illegally.
The law is rarely if ever enforced, but could potentially be used in court to reduce financial compensation if the cyclist were to be hit by another vehicle.
The CTC have suggested that the requirement should be waived if the cyclist fits an additional rear reflector or lighting, but this was not changed in the last revision of the UK vehicle lighting laws (which permitted flashing LEDs).
Riders of recumbent bicycles have pointed out that the pedal reflector requirement is nonsensical for them, since the reflectors point straight up and down in use, and are invisible from other vehicles.
As of 2008, California law allows white or yellow shoe reflectors (front and back), or reflective ankle bands, in lieu of pedal reflectors.