function custom_nextpage_links($defaults) {
                 $args = array(
        'before'     => '<ul class="my-paginated-posts"><ul><li>' . __( 'Section:', 'textdomain' ),
    'after'            => '</li></ul>',
    'link_before'      => '<span class="page-link">',
    'link_after'       => '</span>',
    'separator'        => ' ',
    'nextpagelink'     => __('Next &raquo', 'textdomain'),
    'next_or_number'   => '',
    'previouspagelink' => __( '&laquo Previous', 'textdomain' ),
    'pagelink'         => '%',
    'echo'             => 1
);

$r = wp_parse_args($args, $defaults);

return $r;
}
add_filter('wp_link_pages_args','custom_nextpage_links');