Add IDs to all headings on a page in WordPress

Add a ID attribute for all heading

<?php
add_filter('the_content', 'add_id_attribute_to_headings');

function add_id_attribute_to_headings($content): string {
  return preg_replace_callback('#<(h[1-6])(.*?)>(.*?)</(h[1-6])>#', 'add_id_attribute_to_heading_callback', $content);
}

function add_id_attribute_to_heading_callback($match): string {
  [$full, $el_start, $attributes, $content, $el_end] = $match;

  if (str_contains($full, ' id="')) {
    return $full;
  }

  $id = sanitize_title_with_dashes($content);
  return '<{$el_start} id="{$id}" {$attributes}>{$content}</{$el_end}>';
}