Insert a newly created `w:tab` child element in *pos* order.

def insert_tab_in_order(self, pos, align, leader):
        """
        Insert a newly created `w:tab` child element in *pos* order.
        """
        new_tab = self._new_tab()
        new_tab.pos, new_tab.val, new_tab.leader = pos, align, leader
        for tab in self.tab_lst:
            if new_tab.pos < tab.pos:
                tab.addprevious(new_tab)
                return new_tab
        self.append(new_tab)
        return new_tab