The content's size has changed, its size in the event is the new size.

pan,content_size,changed: Eina.Size2D;

EFL_UI_PAN_EVENT_PAN_CONTENT_SIZE_CHANGED(Eina_Size2D)

static void
on_efl_ui_pan_event_pan_content_size_changed(void *data, const Efl_Event *event)
{
    Eina_Size2D info = event->info;
    Eo *obj = event->object;
    Data *d = data;
 
    /* event hander code */
}
 
static void
setup_event_handler(Eo *obj, Data *d)
{
    efl_event_callback_add(obj, EFL_UI_PAN_EVENT_PAN_CONTENT_SIZE_CHANGED, on_efl_ui_pan_event_pan_content_size_changed, d);
}