Fix .NET XML serialisation bugs by preventing it from passing XML 1.1-only entities in XML 1.0. This is a replacement for the use of the String class.

XmlString.cs

/// <summary>
/// Prevents .NET's XML serialiser from outputting XML 1.0-invalid entities.
/// 
/// Even though none of the .NET Framework supports XML 1.1, it still returns XML 1.1-only
/// entities (like &#x1B;).
/// 
/// This class acts as a wrapper around strings to automatically remove those unsafe escape
/// characters from the string before it is passed to the XML serialiser classes.
/// 
/// In order to use, simply replace instances of the "string" type in your serialised objects
/// with "XmlString".  This will automatically filter out the characters silently in the
/// background.
/// </summary>
[XmlType("string", Namespace = "http://www.w3.org/2001/XMLSchema")]
public class XmlString
{
    private string value;

    [XmlText()]
    public string Value
    {
        get
        {
            return this.value;
        }

        set
        {
            this.value = filterString(value);
        }
    }

    public XmlString()
    {
        // XML serialiser needs a no-args constructor.
    }

    public XmlString(string value)
    {
        this.value = filterString(value);
    }

    private static string filterString(string input)
    {
        string output = "";

        foreach (char c in input)
        {
            // Filter out bad XML characters.
            if (c < '\x20' && c != '\x09' && c != '\x0A' && c != '\x0D')
                // No control characters but TAB, LF and CR are allowed
                continue;
            if (c > '\xD7FF' && c < '\xE000')
                continue;
            output += c;
        }

        return output;
    }

    #region string conversion operators
    public static implicit operator string(XmlString value)
    {
        return value.Value;
    }

    public static implicit operator XmlString(string value)
    {
        return new XmlString(value);
    }
    #endregion
}