docs: def __attrs_str(self, tag, attrs):
          """
          Build string of attributes list for tag
          """
          enabled = self.whitelist.get(tag, ['*'])
          all_attrs = '*' in enabled
          items = []
          for attr in attrs:
              key = attr[0]
              value = attr[1] or ''
              if all_attrs or key in enabled:
                  items.append( u'%s="%s"' % (key, value,) )
          return u' '.join(items)