use CGI qw/:standard/; # this is FO
print header,
      start_html('some title'),
      ...

##</code><code>##

use CGI; # this is OO
my $q = CGI->new;
print $q->header,
      $q->start_html('some title'),
      ...

##</code><code>##

C:\>perl -MCGI -e "print header();"
Undefined subroutine &main::header called at -e line 1.

##</code><code>##

C:\>perl -MCGI -e "print CGI::header();"
Content-Type: text/html; charset=ISO-8859-1

##</code><code>##

sub header {
    my($self,@p) = self_or_default(@_);

##</code><code>##

my $q = CGI->new({});