Accessibility for people with disabilities has a broad scope because of the wide variety of disabilities people may have. There are uses two general approaches to providing accessibility to people with disabilities: direct access, and access via special user agents.
Direct access means content is intrinsically accessible, so all users, including users with disabilities, can benefit from the accessibility features provided. These features are, by definition, supported by mainstream browsers and so require no special support for users to benefit from them. Such features often also benefit users who do not have disabilities, but they provide a disproportionate benefit to users with disabilities.
Access via special user agents, by contrast, involves features that are not seen or used by most users, but can be exploited by assistive technologies. Assistive technologies are software applications or hardware devices designed to assist people with disabilities who would have difficulty or would be unable to use an unmodified mainstream application or device. There are many types of disabilities and therefore many types of assistive technologies, but they have a few things in common:
Each of these two approaches has strengths and weaknesses. Because of its generality, direct access benefits large proportions of users, and the features are portable to different situations. However, the same generality does not meet the needs of users with certain specialized needs. Guidelines about direct access provide parameters and limitations on the design of Web content and thus limit author freedom.
While access via special user agents is not as portable as direct access, it provides greater control and flexibility. Presentation of content is customized to the needs of each specific user. This kind of access is enabled by including features in the content that provide the information needed for assistive technologies to present content and support interaction in different ways. These features do not generally affect display in mainstream user agents, which leads to greater author freedom, but do require specialized attention to ensure the features are provided correctly.
One of the goals of WCAG 2.0 is to minimize its effect on author freedom. Guidelines that impact mainstream presentation tend not to be followed because authors have specific design and content objectives that they are not willing to compromise. Therefore, most of WCAG 2.0, especially at Level 1, specifically involves support for assistive technologies.
The focus on access via special user agents benefits cognitive accessibility as much or more than other types of disabilities. The requirements of users with cognitive and learning disabilities are highly variable and individual. Content that conforms to WCAG 2.0 provides important user control and enables a variety of presentation and interaction modalities needed to address the variety of cognitive, language, and learning disabilities.