code: function sh_extractTags(element, tags) {
    var result = {};
    result.text = [];
    result.tags = tags;
    result.pos = 0;
    sh_extractTagsFromNodeList(element.childNodes, result);
    return result.text.join('');
  }
docs: Extracts the tags from the text of an HTML element. The extracted tags will be
  returned as an array of tag objects. See sh_highlightString for the format of
  the tag objects.
  @param  element  a DOM element
  @param  tags  an empty array; the extracted tag objects will be returned in it
  @return  the text of the element
  @see  sh_highlightString