you really want to count the 'additem' calls inside an action or do you just want to know how many items are there?
the number of items can be get by plugin[comboboxpluginname].item.count,
but if you want to analyze the action code itself, it would be necessary to parse the "action[name].content" by the indexoftxt action and count the 'additem' occurrences, e.g.