public XlFieldAttribute(XlContentType contentType, bool isRequired, params string[] captions) : this(contentType, isRequired) => captions.ForEach(Captions.Add);
 //=================================================
 XlFieldAttribute(XlContentType contentType, bool isRequired)
 {
     ContentType = contentType;
     IsRequired  = isRequired;
     Captions    = new List <string>();
 }