, ,  tags.
  // We don't apply any processing to the contents of these tags to avoid messing
  // up code. We look for matched pairs and allow basic nesting. For example:
  // "processed 
 ignored  ignored 
 processed"
  $chunks = preg_split('@(]*>)@i', $text, -1, PREG_SPLIT_DELIM_CAPTURE);
  // Note: PHP ensures the array consists of alternating delimiters and literals
  // and begins and ends with a literal (inserting NULL as required).
  $ignore = FALSE;
  $ignoretag = '';
  $output = '';
  foreach ($chunks as $i => $chunk) {
    if ($i % 2) {
      // Opening or closing tag?
      $open = ($chunk[1] != '/');
      list($tag) = preg_split('/[ >]/', substr($chunk, 2 - $open), 2);
      if (!$ignore) {
        if ($open) {
          $ignore = TRUE;
          $ignoretag = $tag;
        }
      }
      // Only allow a matching tag to close it.
      elseif (!$open && $ignoretag == $tag) {
        $ignore = FALSE;
        $ignoretag = '';
      }
    }
    elseif (!$ignore) {
      $chunk = preg_replace('|\n*$|', '', $chunk) . "\n\n"; // just to make things a little easier, pad the end
      $chunk = preg_replace('|
\s*
|', "\n\n", $chunk);
      $chunk = preg_replace('!(<' . $block . '[^>]*>)!', "\n$1", $chunk); // Space things out a little
      $chunk = preg_replace('!()!', "$1\n\n", $chunk); // Space things out a little
      $chunk = preg_replace("/\n\n+/", "\n\n", $chunk); // take care of duplicates
      // switch ...
      if ($style == 'new') {
        $chunk = preg_replace('/^\n/', '', $chunk);
        $chunk = '
' . preg_replace('/\n\s*\n\n?(.)/', "
\n
$1", $chunk) . '
'; // make paragraphs, including one at the end
      } else {
        $chunk = preg_replace('/\n?(.+?)(?:\n\s*\n|\z)/s', "
$1
\n", $chunk); // make paragraphs, including one at the end
      }
      
      $chunk = preg_replace("|
(|", "$1", $chunk); // problem with nested lists
      $chunk = preg_replace('|
]*)>|i', "
", $chunk);
      $chunk = str_replace('
', '
', $chunk);
      $chunk = preg_replace('|
\s*
\n?|', '', $chunk); // under certain strange conditions it could create a P of entirely whitespace
      $chunk = preg_replace('!
\s*(]*>)!', "$1", $chunk);
      $chunk = preg_replace('!(]*>)\s*
!', "$1", $chunk);
      $chunk = preg_replace('|(?)\s*\n|', "
\n", $chunk); // make line breaks
      $chunk = preg_replace('!(]*>)\s*
!', "$1", $chunk);
      $chunk = preg_replace('!
(\s*)!', '$1', $chunk);
      $chunk = preg_replace('/&([^#])(?![A-Za-z0-9]{1,8};)/', '&$1', $chunk);
    }
    $output .= $chunk;
  }
  return $output;
}

/**
 * new regex for filter.module  issue http://drupal.org/node/133188
 */
$chunk = "Hello,

Lorem ipsum.

Lorem ipsum.

Last paragraph

";
// this is from _filter_autp
echo "INPUT===============\n";
echo $chunk;
// the two new lines from the patch
$chunk_new = _filter_autop($chunk, 'new');
// 
$chunk_old = _filter_autop($chunk, 'old');
echo "\nNEW REGEX=============\n";
echo $chunk_new;
echo "\nOLD REGEX BACKTRACKING=============\n";
echo $chunk_old;

if ($chunk_new !== $chunk_old) {
  echo "\nWARNING - NEW != OLD\n"; 	
}