code: func (extr *ContentExtractor) GetTags(document *goquery.Document) *set.Set {
  	tags := set.New(set.ThreadSafe).(*set.Set)
  	selections := document.Find(aRelTagSelector)
  	selections.Each(func(i int, s *goquery.Selection) {
  		tags.Add(s.Text())
  	})
  	selections = document.Find("a")
  	selections.Each(func(i int, s *goquery.Selection) {
  		href, exists := s.Attr("href")
  		if exists {
  			for _, part := range aHrefTagSelector {
  				if strings.Contains(href, part) {
  					tags.Add(s.Text())
  				}
  			}
  		}
  	})
  
  	return tags
  }
docs: // GetTags returns the tags set in the source, if the article has them