<?php
class MarkdownWithoutMarkup_Parser extends MarkdownExtra_Parser{
  // allowed HTML tags
  var $allowed_tags;
  // constructor
  function MarkdownWithoutMarkup_Parser() {
    $this->MarkdownExtra_Parser();
    $this->no_markup = true;
    $this->no_entities = true;
  }
  // overload to allow only some HTML tags
  function hashHTMLBlocks($text) {
    return preg_replace_callback('{<('.$this->allowed_tags.')>.*?</\1>}',
      array(&$this, '_hashBlock'),
    $text);
  }
  function _hashBlock($matches) {
    return $this->hashBlock($matches[0]);
  }
  // overload to accept allowed tags
  function transform($input, $allowed_tags) {
    $allowed_tags = preg_split('#[^a-zA-Z1-6]+#', $allowed_tags);
    $this->allowed_tags = implode('|', $allowed_tags);
    return parent::transform($input);
  }
}

function MarkdownWithoutMarkup($text, $allowed_tags = '') {
  static $parser;
  if (!isset($parser)) {
    $parser = new MarkdownWithoutMarkup_Parser;
  }
  $return = $parser->transform($text, $allowed_tags);
  return $return;
}