Constructing a POUR Website
Let's say that web content is perceivable and operable by all kinds of users of all abilities, but it is understandable to none of them. Is the web content accessible? Of course not. Understandability can be just as big a barrier to accessibility as any of the more technical issues. Talking about understandability moves the discussion into the broader realm of usability. Usability became a hot topic in the late nineties and early 21st century. It still is a hot topic, but has moved from being a fringe fad to being a topic of mainstream conversation among web developers. Web accessibility never achieved "fad" status, but awareness of the topic has also increased over time. Unfortunately, too many people still separate usability and accessibility into two separate disciplines. Trying to separate principles into mutually exclusive categories of "usability" versus "accessibility" would be pointless. There is too much of an overlap between the two. After all, could an unusable site ever be considered an accessible site? Not if accessibility means anything.
Most web content contains information communicated through language. The language should be as easy to understand as possible. The wording as well as the words should be simple and concise. How simple and concise? That depends on a number of factors, many of which depend upon the characteristics of the intended audience. Factors such as the audience's educational background, their familiarity with the subject matter, their background knowledge and life experiences, their culture, and so on. Authors do not always know the exact characteristics of their audience, so it is usually best to err on the side of caution by using simple language and explaining background information that readers may not know. Other factors are related to the content itself, such as the level of detail required to understand it, reason for talking about about the subject matter, and so on.
(See also Writing Clearly and Simply.)
Alternative or supplemental representations
Providing alternative or supplemental representations of information can often increase understandability. Text can be supplemented with illustrations, videos, animations, audio, and content in other alternative formats. In fact, for some people with more severe cognitive disabilities or people with reading disabilities, these alternative formats may be necessary for comprehension. Providing summaries or abstracts of lengthy content can also make it more understandable.
The functionality of web content must also be understandable. Users must be able to understand all navigation and other forms of interaction. On static web sites, the interaction may be limited to hypertext links. In more complex Web content, the interaction can be extremely complex, requiring the user to pass through multiple steps or stages, to make decisions along the way, input information, confirm information, and so on. Every point of interaction deserves attention in order to give users the best experience possible. If users don't understand any of the points of interaction, they may not be able to complete the necessary tasks on that web site.
Wherever possible, navigation should be consistent and predictable throughout the context of the web site. Interactive elements such as form controls should also be predictable and should be clearly labeled. Wherever necessary, users should be able to access instructions or receive guidance. If math calculations are involved, such as when subtotaling items in a shopping cart, the math should either be calculated automatically, or else users should be provided with guidance and/or tools on how to perform the calculations.