In a society in which business is increasingly conducted online, excluding businesses that sell services through the Internet from the ADA would ‘run afoul of the purposes of the ADA’” in that it would prevent “‘individuals with disabilities [from] fully enjoy[ing] the goods, services, privileges, and advantages, available indiscriminately to other members of the general public.
As I mentioned above, under each WCAG 2.1 principle is a list of guidelines, and under each guideline are compliance standards, with techniques and failure examples at each level. Some guidelines include only Level A items; others include items for multiple levels of conformance, building from A to AAA. At each stage, you can easily see what more you would need to do to reach Level AA or AAA. In this way, many websites include elements at multiple levels of accessibility.
The ADA is the Americans with Disabilities Act, passed almost 30 years ago in 1990. This act was originally put in motion pertaining solely to physical location. It requires establishments to provide people with disabilities easy access to various levels throughout the business. This act was set to achieve an equal experience to all people, handicapped or not.