docs: def execute_with_style_LEGACY(template, style, data, callback, body_subtree='body'):
      """OBSOLETE old API."""
      try:
          body_data = data[body_subtree]
      except KeyError:
          raise EvaluationError('Data dictionary has no subtree %r' % body_subtree)
      tokens_body = []
      template.execute(body_data, tokens_body.append)
      data[body_subtree] = tokens_body
      tokens = []
      style.execute(data, tokens.append)
      _FlattenToCallback(tokens, callback)