The ResponseParams argument is a list of terms returned by the libwww_request call. It contains two kinds of information: header information and sub-request information. The header information consists of terms like: header('Content-Type', 'text/html'), header('Server', 'Netscape-Enterprise/3.6 SP2'), etc., as defined by the HTTP protocol (header/2 is a functor and its arguments are atoms). The sub-request information consists of terms of the form: subrequest('http://www.foo.org/test/file.html',-401). It indicates that during processing of the current request, it was necessary to access another page, http://www.foo.org/test/file.html, but the server responded with the error code -401 (authentication error). Such sub-requests might be spawned during XML parsing.