How to use the podcastparser.EpisodeAttrRelativeLink function in podcastparser

# If you modify the mapping, don't forget to also update the documentation
# section "Supported XML Elements and Attributes" in doc/index.rst
MAPPING = {
    'rss': RSS(),
    'rss/channel': PodcastItem(),
    'rss/channel/title': PodcastAttr('title', squash_whitespace),
    'rss/channel/link': PodcastAttrRelativeLink('link'),
    'rss/channel/description': PodcastAttr('description', squash_whitespace),
    'rss/channel/image/url': PodcastAttrRelativeLink('cover_url'),
    'rss/channel/itunes:image': PodcastAttrFromHref('cover_url'),
    'rss/channel/atom:link': PodcastAtomLink(),

    'rss/channel/item': EpisodeItem(),
    'rss/channel/item/guid': EpisodeGuid('guid'),
    'rss/channel/item/title': EpisodeAttr('title', squash_whitespace),
    'rss/channel/item/link': EpisodeAttrRelativeLink('link'),
    'rss/channel/item/description': RSSItemDescription(),
    'rss/channel/item/itunes:summary': EpisodeAttr('description', squash_whitespace),
    'rss/channel/item/media:description': EpisodeAttr('description', squash_whitespace),
    'rss/channel/item/itunes:subtitle': EpisodeAttr('subtitle', squash_whitespace),
    'rss/channel/item/content:encoded': EpisodeAttr('description_html'),
    'rss/channel/item/itunes:duration': EpisodeAttr('total_time', parse_time),
    'rss/channel/item/pubDate': EpisodeAttr('published', parse_pubdate),
    'rss/channel/item/atom:link': AtomLink(),

    'rss/channel/item/media:content': Enclosure('fileSize'),
    'rss/channel/item/enclosure': Enclosure('length'),
    'rss/channel/item/psc:chapters': PodloveChapters(),
    'rss/channel/item/psc:chapters/psc:chapter': PodloveChapter(),

    # Basic support for Atom feeds
    'atom:feed': PodcastItem(),

def end(self, handler, text):
        text = urlparse.urljoin(handler.base, text)
        super(EpisodeAttrRelativeLink, self).end(handler, text)