When more than one search service (or service that reads its input from the request attributes) is assigned to a single page, when the user submits one of the forms, each service processes the request and acts and displays accordingly.
Search services should be protected from responding to the other ones' requests, for instance by providing one's ZoneItem ID along with the submit data, and checking this input against itself when processing the data.
Nevertheless, sometimes, we want the form to be displayed in a zone, and the results to be displayed in another. If the above requirement is implemented, the second won't be able to process the results of the first. A parameter "service group ID" should therefore be added to the services, to have the possibility to link the services we want to be able to work together.