code: def _add_tags(self, tags):
          # type: (List[str]) -> bool
          
          alltagsadded = True
          for tag in tags:
              if not self._add_tag(tag):
                  alltagsadded = False
          return alltagsadded
docs: Add a list of tag
  
          Args:
              tags (List[str]): list of tags to add
  
          Returns:
              bool: True if all tags added or False if any already present.