public FilterTextExpression(string text, FilterTextMatching matching)
 {
     if (text == null)
     {
         throw new ArgumentNullException(nameof(text));
     }
     _text     = text;
     _matching = matching;
 }
 protected static bool UseCaseInsensitiveRegexMatching(FilterTextExpression optTxt, FilterTextMatching matching)
 {
     return(!(matching == FilterTextMatching.RegularExpression ||
              optTxt?.Matching == FilterTextMatching.Exact));
 }