https://learn.microsoft.com/en-us/dotnet/api/system.xml.xmlwriter.writebase64?view=netframework-4.8.1&viewFallbackFrom=net-8.0
XmlWriter.WriteBase64(Byte[], Int32, Int32) Method (System.Xml) | Microsoft Learn
When overridden in a derived class, encodes the specified binary bytes as Base64 and writes out the resulting text.
xmlwriterbytemethodsystemmicrosoft