Declare support for Auto Load Next Post in a theme. Last two values are for Auto Load Next Post v1.5.0+ only!

alnp-add-theme-support.php

/**
 * Add theme support for Auto Load Next Post by setting the 
 * theme selectors to be applied once the theme is activated. 
 */
function add_alnp_theme_support() {
  add_theme_support( 'auto-load-next-post', array( 
    'content_container' => 'main.site-main',
    'title_selector' => 'h1.entry-title',
    'navigation_container' => 'nav.post-navigation',
    'comments_container' => 'div#comments',
    'load_js_in_footer' => 'no',
    'lock_js_in_footer' => 'no',
  ) );
}
add_action( 'after_setup_theme', 'add_alnp_theme_support' );