code: func (f *Field) createBSIGroup(bsig *bsiGroup) error {
  	f.mu.Lock()
  	defer f.mu.Unlock()
  
  	// Append bsiGroup.
  	if err := f.addBSIGroup(bsig); err != nil {
  		return err
  	}
  	if err := f.saveMeta(); err != nil {
  		return errors.Wrap(err, "saving")
  	}
  	return nil
  }
docs: // createBSIGroup creates a new bsiGroup on the field.