Break a string without losing html tags in PHP

<?php
/**
* Using this function, we can break(substr) a string without losing html tags,
*
* @param $text
*    String which is to be shortened.
*
* @param $length
*    The length of the string .
*
* @param $ending
*    The string that is to be appended after shortening.  Defaults to &hellip;
*
* @param boolean $exact
*   If false, $text will not be cut mid-word
*
* @param boolean $considerHtml
*   If true, HTML tags would be handled correctly
*
*
* @return
*     string Trimmed string..
*/
Function _html_substr ($text, $length = 100, $ending = '...', $exact = false, $considerHtml = true) {
    if ($considerHtml) {
      // If the plain text is shorter than the maximum length, return the whole text
      if (strlen(preg_replace('/<.*?>/', '', $text)) <= $length) {
        return $text;
      }
      // splits all html-tags to scanable lines
      preg_match_all('/(<.+?>)?([^<>]*)/s', $text, $lines, PREG_SET_ORDER);
      $total_length = strlen($ending);
      $open_tags = array();
      $truncate = '';
      foreach ($lines as $line_matchings) {
        // if there is any html-tag in this line, handle it and add it (uncounted) to the output
        if (!empty($line_matchings[1])) {
          // if it's an "empty element" with or without xhtml-conform closing slash (f.e. <br/>)
          if (preg_match('/^<(\s*.+?\/\s*|\s*(img|br|input|hr|area|base|basefont|col|frame|isindex|link|meta|param)(\s.+?)?)>$/is', $line_matchings[1])) {
            // do nothing
            // if tag is a closing tag (f.e. </b>)
          }
                                  elseif (preg_match('/^<\s*\/([^\s]+?)\s*>$/s', $line_matchings[1], $tag_matchings)) {
            // delete tag from $open_tags list
            $pos = array_search($tag_matchings[1], $open_tags);
            if ($pos !== FALSE) {
              unset($open_tags[$pos]);
            }
              // if tag is an opening tag (f.e. <b>)
          }
                                  elseif (preg_match('/^<\s*([^\s>!]+).*?>$/s', $line_matchings[1], $tag_matchings)) {
            // add tag to the beginning of $open_tags list
            array_unshift($open_tags, strtolower($tag_matchings[1]));
          }
            // add html-tag to $truncate'd text
            $truncate .= $line_matchings[1];
        }
        // calculate the length of the plain text part of the line; handle entities as one character
        $content_length = strlen(preg_replace('/&[0-9a-z]{2,8};|&#[0-9]{1,7};|&#x[0-9a-f]{1,6};/i', ' ', $line_matchings[2]));
        if ($total_length+$content_length> $length) {
          // the number of characters which are left
          $left = $length - $total_length;
          $entities_length = 0;
          // search for html entities
          if (preg_match_all('/&[0-9a-z]{2,8};|&#[0-9]{1,7};|&#x[0-9a-f]{1,6};/i', $line_matchings[2], $entities, PREG_OFFSET_CAPTURE)) {
          // calculate the real length of all entities in the legal range
            foreach ($entities[0] as $entity) {
              if ($entity[1]+1-$entities_length <= $left) {
                $left--;
                                                    $entities_length += strlen($entity[0]);
              }
                                                  else {
                // no more characters left
                break;
              }
            }
          }
          $truncate .= substr($line_matchings[2], 0, $left+$entities_length);
          // maximum lenght is reached, so get off the loop
          break;
        }
                    else {
          $truncate .= $line_matchings[2];
          $total_length += $content_length;
        }
        // if the maximum length is reached, get off the loop
        if ($total_length>= $length) {
          break;
        }
      }
    }
                else {
      if (strlen($text) <= $length) {
        return $text;
      }
                  else {
        $truncate = substr($text, 0, $length - strlen($ending));
      }
    }
    // if the words shouldn't be cut in the middle...
    if (!$exact) {
      // ...search the last occurance of a space..
                  $spacepos = strrpos($truncate, ' ');
      if (isset($spacepos)) {
        // ...and cut the text in this position
        $truncate = substr($truncate, 0, $spacepos);
      }
    }
    // add the defined ending to the text
    $truncate .= $ending;
    if ($considerHtml) {
      // close all unclosed html-tags
      foreach ($open_tags as $tag) {
        $truncate .= '</' . $tag . '>';
      }
    }
    return $truncate;
}
?>