All XKB interactions with the input extension are optional; implementors are free to restrict the effects of the X Keyboard Extension to the core keyboard device. The XkbGetExtensionDeviceInfo request reports whether or not an XKB implementation supports a particular capability for input extension devices. XKB recognizes the following interactions with the X Input Extension: Name Capability XI_Keyboards If set, applications can use all XKB requests and events with extension keyboards. XI_ButtonActions If set, clients can assign key actions to buttons, even on input extension devices that are not keyboards. XI_IndicatorNames If set, clients can assign names to indicators on non-keyboard extension devices. XI_IndicatorMaps If set, clients can assign indicator maps to indicators on non-keyboard extension devices. XI_IndicatorState If set, clients can change the state of device indicators using the XkbSetExtensionDeviceInfo request. Attempts to use an XKB feature with an extension device fail with a Keyboard error if the server does not support the XkbXI_Keyboards optional feature. If a capability particular capability other than XkbXI_Keyboards is not supported, attempts to use it fail silently. The replies for most requests that can use one of the other optional features include a field to report whether or not the request was successful, but such requests do not cause an error condition. Clients can also request an XkbExtensionDeviceNotify event. This event notifies interested clients of changes to any of the supported XKB features for extension devices, or if a request from the client that is receiving the event attempted to use an unsupported feature. All XKB requests and events include a device identifier which can refer to an input extension KeyClass device, if the implementation allows XKB to control extension devices. If the implementation does not support XKB manipulation of extension devices, the device identifier is ignored but it must be either 0 or UseCoreKbd . Implementations which do not support the use of XKB functions with extension keyboards must not set the XkbXI_Keyboards flag. Attempts to use XKB features on an extension keyboard with an implementation that does not support this feature yield a Keyboard error. The XKB extension optionally allows clients to assign any key action (see Key Actions) to core pointer or input extension device buttons. This makes it possible to control the keyboard or generate keyboard key events from extension devices or from the core pointer. XKB implementations are required to support actions for the buttons of the core pointer device, but support for actions on extension devices is optional. Implementations which do not support button actions for extension devices must not set the XkbXI_ButtonActions flag. Attempts to query or assign button actions with an implementation that does not support this feature report failure in the request reply and might cause the server to send an XkbExtensionDeviceNotify event to the client which issued the request that failed. Such requests never cause an error condition. The XKB extension allows applications to assign indicator maps to the indicators of non-keyboard extension devices. If supported, maps can be assigned to all extension device indicators, whether they are part of a keyboard feedback or part of an indicator feedback. Implementations which do not support indicator maps for extension devices must not set the XkbXI_IndicatorMaps flag. Attempts to query or assign indicator maps with an implementation that does not support this feature report failure in the request reply and might cause the server to send an XkbExtensionDeviceNotify event to the client which issued the request that failed. Such requests never cause an error condition. If this feature is supported, the maps for the default indicators on the core keyboard device are visible both as extension indicators and as the core indicators. Changes made with XkbSetDeviceInfo are visible via XkbGetIndicatorMap and changes made with XkbSetIndicatorMap are visible via XkbGetDeviceInfo . The XKB extension allows applications to assign symbolic names to the indicators of non-keyboard extension devices. If supported, symbolic names can be assigned to all extension device indicators, whether they are part of a keyboard feedback or part of an indicator feedback. Implementations which do not support indicator maps for extension devices must not set the XkbXI_IndicatorMaps flag. Attempts to query or assign indicator names with an implementation that does not support this feature report failure in the request reply and might cause the server to send an XkbExtensionDeviceNotify event to the client which issued the request that failed. Such requests never cause an error condition. If this feature is supported, the names for the default indicators on the core keyboard device are visible both as extension indicators and as the core indicators. Changes made with XkbSetDeviceInfo are visible via XkbGetNames and changes made with XkbSetNames are visible via XkbGetDeviceInfo .