Lemon laws primarily serve to force manufacturers to buy back defective vehicles or exchange them. Depending on the jurisdiction, a process similar to vehicle title branding may also be used to warn subsequent purchasers of the history of a problem vehicle. While this portion of a vehicle's history is usually not retained with the title when exporting it to another jurisdiction, at least one jurisdiction (California) has started compelling manufacturers to brand the titles of any previously reacquired vehicles that they import or export from the jurisdiction. While used cars may be plagued with the same problems that beset new vehicles, used vehicles may also have been abused, improperly maintained or poorly repaired, been unprofessionally rebuilt after a collision or tampered with in some manner to conceal high mileage, mechanical defects, corrosion or other damage. One form of lemon is called a cut and shut or clipping, a form of body collision "repair" based on buying a wrecked car and sawing off the wrecked section to replace it with a matching section from another (similar) car. If improperly repaired, these vehicles may be inherently dangerous; at high speeds, or in an accident, the car may come apart due to the weaknesses of the welds or pins connecting the two segments of the vehicle or mismatches of segments. In the UK "cut and shut" cars are treated like any car that has had major repair work resulting in what is essentially a new car. They must first be inspected for road-worthiness, be assigned a new registration number and pass the standard MOT test. If this is successful, they will be given a "Q" registration, meaning they are a kit, or composite car, and not an original unit from the manufacturer. In some states of the USA, the sale of "cut and shut" vehicles is illegal. Cars created using two or more large sections of previous ones are sometimes called "zipper cars". Improperly repaired collision-damage vehicles also carry the risk of unibody problems. Unlike heavy trucks and lorries, most passenger cars manufactured since 1987 employ unibody construction instead of a separate body and frame. This saves weight, but the unibody is prone to bend (it is designed to do so in an impact, to absorb part of the energy of the shock) or suffer damage in severe collisions, causing the vehicle not to handle correctly or causing other mechanical parts to wear prematurely if the damaged unibody vehicle is driven after an accident. Today, there are vehicle history services that can help a prospective used car buyer by providing a "history report" based on the vehicle's identification number (VIN).