This GPL implementation expects all external character data to be encoded in UTF-8. Since 7-bit ASCII characters are a subset of UTF-8, all data will be properly interpreted if you confine your data to the 7-bit ASCII subset.
In addition, XML text files include certain special characters to delimit data sections. The critical characters are " (double quote), & (ampersand), ' (apostrophe), < (less than), and > (greater than). You must not use these characters in any name or data fields when creating tree nodes or setting node values. For efficiency, GPL does not automatically check for these characters or convert them. If you need to use these characters, you can encode them with the method XmlDoc.EncodeEntities. If you receive data with encoded entities, you can change them to normal 7-bit ASCII with the method XmlDoc.DecodeEntities.