Search handlers allow you to provide a custom search capability for any resource. A search request is delegated to a search handler if required and optional parameters are matched. If there are 2 or more search handlers matching the same request for the given resource, then a search id needs to be specified in the request (e.g. ?s=default).
Please note that you should not use single letter parameters (aside from q) as required or optional parameters for your search handler. They are reserved for the framework use.