sub unknown_mode
{
    my ( $self, $requested ) = (@_);
    my $q        = $self->query();
    my $session  = $self->param('session');
    my $username = $session->param('logged_in');

    $requested = HTML::Entities::encode_entities($requested);

    if ( defined($username) && length($username) )
    {
        return "<p>unknown mode '$requested' for logged in user $username</p>";
    }
    else
    {
        return "<p>Unknown mode '$requested' for anonymous user.</p>";
    }
}