ExcelFormulaParser.Engine.ExcelUtilities.NumericExpressionEvaluator.GetNonNumericStartChars C# (CSharp) Method

        private string GetNonNumericStartChars(string expression)
        {
            if (!string.IsNullOrEmpty(expression))
            {
                if (Regex.IsMatch(expression, @"^([^\d]{2})")) return expression.Substring(0, 2);
                if (Regex.IsMatch(expression, @"^([^\d]{1})")) return expression.Substring(0, 1);
            }
            return null;
        }