code: func ParseFile(files ...string) ([]*Group, error) {
  	var groups []*Group
  	for _, file := range files {
  		if err := func(file string) error {
  			f, err := os.Open(file)
  			if err != nil {
  				return err
  			}
  			defer f.Close()
  			gs, err := Parse(file, f)
  			if err != nil {
  				return err
  			}
  			groups = append(groups, gs...)
  			return nil
  		}(file); err != nil {
  			return nil, err
  		}
  	}
  	return groups, nil
  }
docs: // ParseFile parses the specified files.