XPGetWidgetProperty

WIDGET_API intptr_t   XPGetWidgetProperty(
                         XPWidgetID           inWidget,    
                         XPWidgetPropertyID   inProperty,    
                         int *                inExists);    /* Can be NULL */

This routine returns the value of a widget’s property, or 0 if the property is not defined. If you need to know whether the property is defined, pass a pointer to an int for inExists; the existence of that property will be returned in the int. Pass NULL for inExists if you do not need this information.