https://learn.microsoft.com/en-us/dotnet/api/system.configuration.configurationelement.ondeserializeunrecognizedelement?view=netframework-4.8.1&redirectedfrom=MSDN
ConfigurationElement.OnDeserializeUnrecognizedElement Method (System.Configuration) | Microsoft...
Gets a value indicating whether an unknown element is encountered during deserialization.
system configurationmethodmicrosoft