For example, a step from the living room out onto the balcony can be very dangerous as a tripping hazard for the elderly and people with impaired movement. A flat frame structure developed by YKK AP employs ingenuities, such as a stepless entry and designs providing safe mobility, even in a wheelchair, and handles which open and close windows easily, with little pressure, even for small children and elderly residents, to offer comfortable and long-lasting living spaces where many different people can live.