about yahoo UI 2.6 data source

hi,     I am using yahoo UI autocomplete in my rails application.      I want to use XML data format.      I have a tag_list field in view file.      this is my code in controller       def filter_tag        @tags= Tags.find(:all)        end

       I can not understand how can I format the resultant data(@tags) in xml format for response.        please give me some example source. I have googled a lot but not find any example for that.        I am very new with the yahoo iu. I have configure the view according to the documentation of yahoo ui autocomplete but trouble with code in the method in the controller.        Please guide me.        Amin