?PATTERN?
      This is just like the /pattern/ search, except that it matches
      only once between calls to the reset() operator.  This is a
      useful optimization when you want to see only the first
      occurrence of something in each file of a set of files, for
      instance.  Only ??  patterns local to the current package are
      reset.

           while (<>) {
               if (?^$?) {
                             # blank line between header and body
               }
           } continue {
               reset if eof; # clear ?? status for next file
           }

       This usage is vaguely deprecated, which means it just might
       possibly be removed in some distant future version of Perl,
       perhaps somewhere around the year 2168.