Built-in Accessibility Features

The built-in accessibility features are extensions to the operating system. These features affect the behavior of the system regardless of which applications are running.

Win32 supports the following built-in accessibility features:

Feature	Description
AccessTimeout	Enables a user to specify a timeout interval after which system-wide accessibility features are automatically disabled. The AccessTimeout feature is intended for computers that are shared by several users with different preferences. Each individual can use hot keys or the Control Panel to enable preferred features. After a user leaves, the features he or she enabled will be automatically disabled by the timeout. The accessibility features affected by the timeout are FilterKeys, MouseKeys, StickyKeys, and ToggleKeys, and High Contrast. The ACCESSTIMEOUT structure defines the parameters for this feature.
FilterKeys	Enables control of keyboard properties, such as the amount of time before a keystroke is accepted as input and the amount of time before a keystroke begins to repeat. The FilterKeys feature also provides sound feedback when a key is pressed and when it is accepted as input. The FILTERKEYS structure defines the parameters for this feature.
MouseKeys	Enables the user to control the mouse pointer using the numeric keypad. The MOUSEKEYS structure defines the parameters for this feature.
SerialKeys	Enables the user to provide input using an alternate input device attached to the computer's serial port. This feature is designed for users who are unable to use the computer's standard keyboard and mouse. The SERIALKEYS structure defines the parameters for this feature.
SoundSentry	Displays a visual signal when a sound is generated by a Win32-based application or an MS-DOS application running in a window. The SOUNDSENTRY structure defines the parameters for this feature, including the address of the SoundSentryProc callback function.
StickyKeys	Enables the user to type key combinations, such as ctrl+alt+del, in sequence rather than at the same time. The STICKYKEYS structure defines the parameters for this feature.
ToggleKeys	Provides sound feedback when the user turns on or off the caps lock, num lock, or scroll lock keys. The TOGGLEKEYS structure defines the parameters for this feature.

The SystemParametersInfo function provides the programming interface to the built-in accessibility features. This function is useful in Control Panel applications or other programs that allow the user to customize the environment. The SystemParametersInfo function can perform the following tasks:

Query the system to determine the availability and current state of a specified built-in accessibility feature
Enable a feature and specify parameters that control its behavior
Disable a feature
Enable a hot key that allows the user to enable or disable a feature

For each of the built-in features, Win32 defines a structure that applications use with SystemParametersInfo to query or set the parameters of the feature.

An application can use SystemParametersInfo to enable or disable a feature directly. For some of the features, SystemParametersInfo can enable a hot key or key combination so the user can toggle the state of a feature. There are no hot keys for the SerialKeys or SoundSentry features, or for the ShowSounds parameter. The following accessibility features have hot keys:

Feature	Description
FilterKeys	Hold down the left shift key for eight seconds to toggle the FilterKeys feature on or off. Holding down the left shift key for 12 seconds enables FilterKeys using the most conservative values for FILTERKEYS.iBounceMSec. Holding down the left shift key for 16 seconds enables FilterKeys using the most conservative values for FILTERKEYS.iWaitMSec.
MouseKeys	Press LEFT ALT + LEFT SHIFT + NUM LOCK.
StickyKeys	Press the shift key 5 times.
ToggleKeys	Hold down the num lock key for 5 seconds.
High Contrast parameter	Press LEFT ALT + LEFT SHIFT + PRINT SCREEN.