public static void AddElementEventFeature(this OpenXmlPackage package)
{
if (package.Features.Get <IElementEventFeature>() is null)
{
package.AddPartRootEventsFeature();
var rootEvent = package.Features.GetRequired <IPartRootEventsFeature>();
package.Features.SetDisposable <IElementEventFeature>(new ElementEventFeature(rootEvent));
}
}