WCAG 2 Layers of Guidance The individuals and organizations that use WCAG vary widely and include Web designers
               and developers, policy makers, purchasing agents, teachers, and students. In order
               to meet the varying needs of this audience, several layers of guidance are provided
               including overall principles , general guidelines , testable success criteria and a rich collection of sufficient techniques , advisory techniques , and documented common failures with examples, resource links and code. Principles - At the top are four principles that provide the foundation for Web accessibility: perceivable, operable, understandable, and robust . See also Understanding the Four Principles of Accessibility . Guidelines - Under the principles are guidelines.