code: func (c *Client) RegionList(lr *ListRange) ([]Region, error) {
  	req, err := c.NewRequest("GET", "/regions", nil, nil)
  	if err != nil {
  		return nil, err
  	}
  
  	if lr != nil {
  		lr.SetHeader(req)
  	}
  
  	var regionsRes []Region
  	return regionsRes, c.DoReq(req, &regionsRes)
  }
docs: // List existing regions.
  //
  // lr is an optional ListRange that sets the Range options for the paginated
  // list of results.