docs: def slugify(string):
      """Return a slug for the unicode_string.
  
      (lowercase, only letters and numbers, hyphens replace spaces)
      """
      filtered_string = []
      if isinstance(string, str):
          string = unicode(string, 'utf-8')
      for i in unicodedata.normalize('NFKC', string):
          cat = unicodedata.category(i)[0]
          # filter out all the non letter and non number characters from the
          # input (L is letter and N is number)
          if cat in 'LN' or i in '-_':
              filtered_string.append(i)
          elif cat in 'Z':
              filtered_string.append(' ')
      return re.sub('\s+', '-', ''.join(filtered_string)).lower()