gtk:toolbar-insert (toolbar item &optional pos)

toolbar -- a gtk:toolbar widget
item -- a gtk:tool-item widget
pos -- an optional integer with the position of the new item, the default value is -1

Insert a gtk:tool-item widget into the toolbar at position pos. If the pos argument is 0 the item is prepended to the start of the toolbar. If the pos argument is negative, the default, the item is appended to the end of the toolbar.