Add Custom Allowed Tags to WordPress Function File

wp_custom_allowed_tags.php

if(!function_exists('custom_add_allowed_tags')) {
  function custom_add_allowed_tags($tags) {

    // iframe
    $tags['iframe'] = array(
      'src'             => array(),
      'height'          => array(),
      'width'           => array(),
      'frameborder'     => array(),
      'allowfullscreen' => array(),
    );
    // form fields - input
    $tags['input'] = array(
      'class' => array(),
      'id'    => array(),
      'name'  => array(),
      'value' => array(),
      'type'  => array(),
    );
    // select
    $tags['select'] = array(
      'class'  => array(),
      'id'     => array(),
      'name'   => array(),
      'value'  => array(),
      'type'   => array(),
    );
    // select options
    $tags['option'] = array(
      'selected' => array(),
    );
    // style
    $tags['style'] = array(
      'types' => array(),
    );
  
    return $tags;
  }
  add_filter('wp_kses_allowed_html', 'custom_add_allowed_tags');
}