XtAppAddActionHook, XtRemoveActionHook - register an action hook procedure
#include <X11/Intrinsic.h>
XtActionHookId XtAppAddActionHook(XtAppContext
    app_context, XtActionHookProc proc, XtPointer
    client_data);
void XtRemoveActionHook(XtActionHookId id);
  - app_context
- Specifies the application context.
- proc
- Specifies the action hook procedure.
- num_args
- Specifies the application-specific data to be passed to the action
    hook.
XtAppAddActionHook adds the specified procedure to the front of a list
  maintained in the application context. In the future, when an action routine
  is about to be invoked for any widget in this application context, either
  through the translation manager or via XtCallActionProc, the action
  hohok procedures will be called in reverse order of registration jut prior to
  invoking the action routine.Action hook procedures are removed automatically and the
    XtActionHookId s destroyed when the application context in which they
    were added is destroyed.
XtRemoveActionHook removes the specified action hook
    procedure from the list in which it was registered.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface