code: def merge_annotations(system, document):
          
          if not Path(document).exists():
              return
          meta = FileSystem.load_yaml(document)
          click.secho('merge: {0}'.format(document.name), fg='blue')
          for identifier, data in meta.items():
              symbol = system.lookup(identifier)
              if symbol:
                  merge(symbol.tags, data)
docs: Read a YAML document and for each root symbol identifier
          updates the tag information of that symbol