package MyCGIApp;

use base 'CGI::Application';
use CGI::Application::Plugin::AutoRunmode;

sub setup {

    ... load database ...
    ... load session  ...
    ... other setup stuff...

}

sub runmode1 : Runmode {

  my $html_output = '';
  $html_output .= $q->start_html(-title=>'petnuch.com',
                                 -style=>{-src=>'/css/layout.css'});
  $html_output .= $self->banner;
  $html_output .= $self->menu;

  require 'MyCGIApp::Runmode1';
  # do_runmode1 is defined in MyCGIApp::Runmode1

  $html_output .= $self->do_runmode1;

  $html_ouput .= $self->footer;

  return $html_output;

}

/* Common functions to every web page */
sub banner {
...
}

sub menu {
...
}

sub footer {
...
}

1;

##</code><code>##

package MyCGIApp::Runmode1;

use strict;
use Runmode1specficmodules;

sub do_runmode1 {

  my $self = shift;
  my $session = $self->session;
  my $q = $self->query();
  my $id = $q->param('n');

  unless( somecondition ) return $self->error;
 
 ...do stuff...

  return $html_output;

}

sub error {

  ...runmode1 error stuff...

}

1;