In addition to the Principles, there is another core concept to Universal Design: the role of the user-expert.
"A user/expert can be anyone who has developed natural experience in dealing with the challenges of our built environment. User/experts include parents managing with toddlers, older people with changing vision or stamina, people of short stature, limited grasp or who use wheelchairs. These diverse people have developed strategies for coping with the barriers and hazards they encounter everyday. The experience of the user/expert is usually in strong contrast to the life experience of most designers and is invaluable in evaluating both existing products and places as well as new designs in development."
[Ostroff, Elaine. INNOVATION, the Quarterly Journal of the Industrial Designers Society of America (IDSA), Volume 16, No. 1 1997.]