for _, override := range contentTypeDefinition.Overrides {
	f := zipFiles[override.PartName]

	switch {
	case override.ContentType == "application/vnd.openxmlformats-package.core-properties xml":
		rc, err := f.Open()
		if err != nil {
			return "", nil, fmt.Errorf("error opening '%v' from archive: %v", f.Name, err)
		}
		defer rc.Close()
}