In the demo skin, in skins\demo\stylesheets\search.xsl, the name of the input field is "textfield". But this one, depends of the service parameter search criteria selected. If the search service is configured with full text field, the name of the input field of the skin should be user.input.criterion.common$wording$textfield$1

We need something that works with all search criteria and not have to be modified in each skin as often as the user contributor modify the search criteria of the service.