code: func (c *Client) renderOptions(opts []grpc.CallOption) (*Options, error) {
  	var options *Options
  	if c.Options != nil {
  		cpy := *c.Options
  		options = &cpy
  	} else {
  		options = DefaultOptions()
  	}
  	if err := options.apply(opts); err != nil {
  		return nil, err
  	}
  	return options, nil
  }
docs: // renderOptions copies client options and applies opts.