European manufacturers of information technology, audio and video equipment work to this document because it provides the route to the CE marking under the safety directive, and the change of principle it introduced is the reason it replaced two separate standards. Instead of prescribing how a product should be built and then testing it, the standard requires the design engineer to identify the energy sources inside the equipment, classify each according to its magnitude, and then provide a safeguard matched to that class, whether it be insulation, a physical barrier, an interlock or an instruction to the user. A design reviewed in this way can absorb a new battery chemistry or a higher power supply without a revision of the standard, which is what made the approach attractive to a fast moving product sector. The document also defines the tests that verify the safeguards and the temperature and fault conditions associated with them.