PHPTableOfContents.php

<?php
/**
   * Use whatever method you like to grab your HTML string. We'll use a site I mentioned in this post
   * as an example.
   */
$remote_site_data = file_get_contents('http://www.10stripe.com/articles/automatically-generate-table-of-contents-php.php');
$dom_document = new DomDocument();
@$dom_document->loadHTML($remote_site_data);
$headers = $dom_document->getElementsByTagName('h2');
foreach ($headers as $header) {
   $table_of_contents[] = trim($header->nodeValue);
}
var_dump($table_of_contents);
/**
array(5) {
  [0]=>
  string(10) "Motivation"
  [1]=>
  string(11) "This script"
  [2]=>
  string(12) "How it works"
  [3]=>
  string(3) "Fin"
  [4]=>
  string(17) "About the Author"
}
*/
/* Pull out one class
foreach ($headers as $header) {
   if ($header->getAttribute('class') == 'specialclassname') {
      $table_of_contents[] = trim($header->nodeValue);
   }
}
*/