Function XPCreateCustomWidget 

pub unsafe extern "C" fn XPCreateCustomWidget(
    inLeft: c_int,
    inTop: c_int,
    inRight: c_int,
    inBottom: c_int,
    inVisible: c_int,
    inDescriptor: *const c_char,
    inIsRoot: c_int,
    inContainer: XPWidgetID,
    inCallback: XPWidgetFunc_t,
) -> XPWidgetID

XPCreateCustomWidget

This function is the same as XPCreateWidget except that instead of passing a class ID, you pass your widget callback function pointer defining the widget. Use this function to define a custom widget. All parameters are the same as XPCreateWidget, except that the widget class has been replaced with the widget function.