/// <summary>
/// Get Non-Main Part of current package
/// </summary>
/// <param name="package">current package</param>
/// <returns>Return non-main part of current package, null if not exist.</returns>
public static IEnumerable <OpenXmlPart> NonMainParts(this OpenXmlPackage package)
{
return(package.DescendantParts()
.Where(p => p.IsReflectable() && !p.IsMainPart()));
}