Users of various systems in various environments can experience temporary or permanent accessibility difficulties. Potential users of systems need to evaluate whether the systems will be accessible to them in the intended environments in which they will be used. Where accessibility can be insufficient, either due to environmental barriers or poor design, these users can wish to resort to assistive technologies (ATs) to provide the required level of accessibility. Currently, there is no common framework for describing accessibility needs or abilities. This requires each potential user to develop their own evaluation method, and then to investigate and evaluate various systems and ATs using this method. However, due to the lack of an existing method, there might also be a lack of suitable information on the abilities of different systems and ATs, leading to inefficiency, confusion, frustration and a general lack of satisfaction by the user.
ISO/IEC 24756:2009 introduces a model of accessibility as a basis for understanding access issues with the interactions between users and systems in various environments. It further describes logical operators used along CAPs to qualify and combine them. It then specifies methods to apply a CAP.