/// <summary>
/// Add alternate content
/// </summary>
/// <param name="alternateContent"></param>
/// <returns></returns>
private string AddAlternateContent(AlternateContent alternateContent)
{
foreach (OpenXmlElement element in alternateContent.Elements())
if (element is AlternateContentFallback)
return AddAlternateContentFallback((AlternateContentFallback)element);
return "";
}