XmAddProtocolCallback — A VendorShell function that adds
client callbacks for a protocol

     #include <Xm/Protocols.h>
void XmAddProtocolCallback(
Widget shell,
Atom property,
Atom protocol,
XtCallbackProc callback,
XtPointer closure);

     XmAddProtocolCallback adds client callbacks for a
protocol. It checks if the protocol is registered, and if it
is not, calls XmAddProtocols. It then adds the callback to
the internal list. These callbacks are called when the
corresponding client message is received.

     XmAddWMProtocolCallback is a convenience interface.  It
calls XmAddProtocolCallback with the property value set to
the atom returned by interning WM_PROTOCOLS.

shell     Specifies the widget with which the protocol
          property is associated

property  Specifies the protocol property

protocol  Specifies the protocol Atom

callback  Specifies the procedure to call when a protocol
          message is received

closure   Specifies the client data to be passed to the
          callback when it is invoked

     For a complete definition of VendorShell and its
associated resources, see VendorShell(3).

     VendorShell(3), XmAddWMProtocolCallback(3),
XmInternAtom(3), and XmRemoveProtocolCallback(3).