'Now detect some relative URL\'s (also using regexs)'

def _extract_relative_urls(self, doc_string):

    relative_urls = RELATIVE_URL_RE.finditer(doc_string)
    filter_false_urls = self._filter_false_urls
    for url_mo in filter(filter_false_urls, relative_urls):
        if self._require_quotes:
            if (not self._is_quoted(url_mo, doc_string)):
                continue
        try:
            url = self._base_url.url_join(url_mo.group(0)).url_string
            url = URL(self._decode_url(url), encoding=self._encoding)
        except ValueError:
            pass
        else:
            url_lower = url.url_string.lower()
            if (url_lower.startswith('http://') or url_lower.startswith('https://')):
                self._re_urls.add(url)
