C # filters invalid characters for XML (hexadecimal value 0x1d)

The exception that is thrown when the XML is loaded or saved. System.ArgumentException: "(hexadecimal value 0x1d) is an invalid character.
The reason for this is that the XML file contains low nonprinting characters
Processing method: When the XML file is generated, filter low nonprinting characters

Replaces the Low-order ASCII character in a string with the & #x character
Convert ASCII 0-8->-
Convert ASCII 11-12->-
Convert ASCII 14-31->- [HTML] view plain copy return System.Text.RegularExpressions.Regex.Replace (httputilit Y.htmlencode (str), @ "[\x00-\x08]| [\x0b-\x0c]| [\x0e-\x1f] "," "");

[CSharp]   View plain copy/// <summary>  ///  replaces the   low-order bit  ASCII  character   in a string     character   ///  conversion   ASCII  0 - 8  ->   -   ///  Conversion   ASCII 11 - 12 ->   -    ///  Conversion   ASCII 14 - 31 ->  -   ///  </summary>  /// <param name= "tmp" ></param>  ///  <returns></returns>   Public static string replaceloworderasciicharacters ( string tmp)    {       StringBuilder info = new  StringBuilder ();       foreach  (char cc in tmp)        {           int ss =  ( INT) cc;           if  ((ss >= 0)  & &  (ss <= 8))  | |   ((ss >= 11)  &&  (ss <= 12))  | |   ((ss >= 14)  &&  (ss <= 32))                 info. AppendFormat ("{0:x};",  ss);           else info. Append (cc);       }       return info. ToString ();  }  /// <summary>  ///  replaces the following characters in a string with the   Low-order bit  ASCII  character   ///  conversion     -   -> ascii  0  - 8  ///  conversion     -    -> ascii 11 -  12  ///  Conversion &NBSP;&NBSP;&NBSP;-&NBSP;&NBsp;-> ascii 14 - 31  /// </summary>  /// <param  name= "Input" ></param>  /// <returns></returns>   public  static string getloworderasciicharacters (string input)    {        if  (String. IsNullOrEmpty (input))  return string. empty;       int pos, startIndex = 0, len =  Input. length;       if  (len <= 4)  return input;       stringbuilder result = new stringbuilder ();        while  (Pos = input. IndexOf ("",  startindex)  >= 0)        {            bool needReplace = false;    &Nbsp;      string roldv = string. Empty, rnewv = string. empty;           int le =  (Len - pos &NBSP;&LT;&NBSP;6)  ? len - pos : 6;            int p = input. IndexOf (";",  pos, le);