t>: User name and password used for
authentication. Defaults to "<tt>ftp:anonymous@anonymous.org</tt>";
<li><tt>command</tt>: The FTP command used to obtain data. Defaults to
"<tt>retr</tt>", but see example below;
<li><tt>port</tt>: The port to used for the control connection. Defaults to 21;
<li><tt>type</tt>: The transfer mode. Can take values "<tt>i</tt>" or
"<tt>a</tt>". Defaults to whatever is the server default;
<li><tt>step</tt>: 
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a>
