my $attributes = $sibling_element->atts();
$attributes->{'#CDATA'} = 1;

# '#CDATA' attribute is defined here
my $elt1 = XML::Twig::Elt->new('present', $attributes, 'This is in CDATA');

# '#CDATA' attribute is undefined here
my $elt2 = XML::Twig::Elt->new('missing', $attributes, 'This is not in CDATA');