There are a number of accessibility aids to assist users with certain types of disabilities. To allow these users to effectively interact with your application, make certain it is compatible with these utilities. This section briefly describes the types of utilities and how they work.
One of the best ways to accommodate accessibility in your software's interface is to use standard Windows conventions wherever possible. Windows already provides a certain degree of customization for users and most accessibility aids work best with software that follows standard system conventions.
Screen enlargers (also referred to as screen magnification utilities or large print programs) allow users to enlarge a portion of their screen. They effectively turn the computer monitor into a viewport showing only a portion of an enlarged virtual display. Users then use the mouse or keyboard to move this viewport to view different areas of the virtual display. Enlargers also attempt to track where users are working, following the input focus and the activation of windows, menus, and secondary windows, and can automatically move the viewport to the active area.
People who cannot use the visual information on the screen can interpret the information with the aid of a screen review utility (also referred to as a screen reader program or speech access utility). Screen review utilities take the displayed information on the screen and direct it through alternative media, such as synthesized speech or a refreshable Braille display. Because both of these media present only text information, the screen review utility must render other information on the screen as text; that is, determine the appropriate text labels or descriptions for graphical screen elements. They must also track users' activities to provide descriptive information about what the user is doing. These utilities often work by monitoring the system interfaces that support drawing on the screen. They build an off-screen database of the objects on the screen, their properties, and their spatial relationships. Some of this information is presented to
users as the screen changes, and other information is maintained until users request it. Screen review utilities often include support for configuration files (also referred to as set files or profiles) for particular applications.
Users who have difficulty typing can choose a voice input system (also referred to as a speech recognition program) to control software with their voice instead of a mouse and keyboard. Like screen reader utilities, voice input systems identify objects on the screen that users can manipulate. Users activate an object by speaking the label that identifies the object. Many of these utilities simulate keyboard interfaces, so if your software includes a keyboard interface, it can be adapted to take advantage of this form of input.
Some individuals with physical disabilities cannot use a standard keyboard, but can use special devices designed to work with an on-screen keyboard. Switching devices display groups of commands displayed on the screen, and the user employs one or more switches to choose a selected group, then a command within the group. Another technique allows a user to use a special mouse or headpointer (a device that lets users manipulate the mouse pointer on the screen through head motion) to point to graphic images of keys displayed on the screen to generate keystroke input.
Impaired physical abilities, such as erratic motion, tremors, or slow response, can sometimes be compensated by filtering out inappropriate keystrokes. The Windows Accessibility Options supports a wide range of keyboard filtering options. These are generally independent of the application with which users are interacting and therefore require no explicit support except for the standard system interfaces for keyboard input. However, users relying on these features may type slowly.