_filter_autop

_filter_autop($text)

function _filter_autop($text) {
  // All block level tags
  $block = '(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|select|option|form|map|area|blockquote|address|math|input|p|h[1-6]|fieldset|legend|hr|article|aside|details|figcaption|figure|footer|header|hgroup|menu|nav|section|summary)';

  // Split at opening and closing PRE, SCRIPT, STYLE, OBJECT, IFRAME tags
  // and comments. 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 <pre> ignored <script> ignored </script> ignored </pre> processed"
  $chunks = preg_split('@(<!--.*?-->|</?(?:pre|script|style|object|iframe|!--)[^>]*>)@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) {
      $comment = (substr($chunk, 0, 4) == '<!--');
      if ($comment) {
        // Nothing to do, this is a comment.
        $output .= $chunk;
        continue;
      }
      // 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('|<br />\s*<br />|', "\n\n", $chunk);
      $chunk = preg_replace('!(<' . $block . '[^>]*>)!', "\n$1", $chunk); // Space things out a little
      $chunk = preg_replace('!(</' . $block . '>)!', "$1\n\n", $chunk); // Space things out a little
      $chunk = preg_replace("/\n\n+/", "\n\n", $chunk); // take care of duplicates
      $chunk = preg_replace('/^\n|\n\s*\n$/', '', $chunk);
      $chunk = '<p>' . preg_replace('/\n\s*\n\n?(.)/', "</p>\n<p>$1", $chunk) . "</p>\n"; // make paragraphs, including one at the end
      $chunk = preg_replace("|<p>(<li.+?)</p>|", "$1", $chunk); // problem with nested lists
      $chunk = preg_replace('|<p><blockquote([^>]*)>|i', "<blockquote$1><p>", $chunk);
      $chunk = str_replace('</blockquote></p>', '</p></blockquote>', $chunk);
      $chunk = preg_replace('|<p>\s*</p>\n?|', '', $chunk); // under certain strange conditions it could create a P of entirely whitespace
      $chunk = preg_replace('!<p>\s*(</?' . $block . '[^>]*>)!', "$1", $chunk);
      $chunk = preg_replace('!(</?' . $block . '[^>]*>)\s*</p>!', "$1", $chunk);
      $chunk = preg_replace('|(?<!<br />)\s*\n|', "<br />\n", $chunk); // make line breaks
      $chunk = preg_replace('!(</?' . $block . '[^>]*>)\s*<br />!', "$1", $chunk);
      $chunk = preg_replace('!<br />(\s*</?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)>)!', '$1', $chunk);
      $chunk = preg_replace('/&([^#])(?![A-Za-z0-9]{1,8};)/', '&amp;$1', $chunk);
    }
    $output .= $chunk;
  }
  return $output;
}