Basically it allows answer items to post their user answers to other answer items which decided to subscribe to the publisher answer item.

 

Creating a subscriber is very easy, currently the answer item that implements the subscriber features is the Subscriber - Xml list type. This type will collect the answer published by the publisher its subscribing to and use the value to load dynamically an Xml file based on this value and populate a dropdownlist.

 

To create a subscriber you can add a new answer item with the Subscriber - Xml list type to your question, once added click again edit on this type ... Now you will see a new "Connections" feature part where you can choose from which answer item it will receive answers. Once you've set it up to subscribe to a publisher what will happen when a user takes the survey is that on form submission, the publisher will send its answer to the subscribing answer item and do his job (here loading the xml and populating the dropdownlist) ... 

 

This model is currently used with countries / regions but you could also use it using your own Xml source files with categories / products, departement / employees ... etc ... Possibilities are endless as the Subscriber - Xml list type can also act as a publisher and those you could create several dynamic answers each of them being based on the other answers.