private string ItemToPattern(ISingleCharRx expr)
 {
     var subClass = expr as IClassRx;
     if (subClass != null && Positive != subClass.Positive)
     {
         throw new ArgumentException("Cannot mix positive and negative character classes", "expr");
     }
     return expr.PatternInsideClass;
 }
        private string ItemToPattern(ISingleCharRx expr)
        {
            var subClass = expr as IClassRx;

            if (subClass != null && Positive != subClass.Positive)
            {
                throw new ArgumentException("Cannot mix positive and negative character classes", "expr");
            }
            return(expr.PatternInsideClass);
        }