The POST method also supports the `multi-
           part/form-data' content used for Form-based File
           Upload as specified in RFC 1867.  You trigger this
           content format by specifying a content type of
           `'form-data'' as one of the request headers.  If one
           of the values in the $form_ref is an array reference,
           then it is treated as a file part specification with
           the following interpretation:

             [ $file, $filename, Header => Value... ]

           The first value in the array ($file) is the name of a
           file to open.  This file will be read and its content
           placed in the request.  The routine will croak if the
           file can't be opened.  Use an `undef' as $file value
           if you want to specify the content directly.  The
           $filename is the filename to report in the request.
           If this value is undefined, then the basename of the
           $file will be used.  You can specify an empty string
           as $filename if you don't want any filename in the
           request.