The patch looks bit weird, but I can´t strip it further to the question right now.
Basically it takes a symbol/string and adds it to the [coll] (which I chose for easier insert/delete actions later). On the left there is some initialization and the gate is for that case when the list is empty.
The [thresh]-behaviour is required for the tab-message that is send to the [tab], which means after [route symbol].
I added a missing dump-msg to the right [trigger], as well as some monitoring. [zl group] doesn´t work but maybe it is set up wrong here.