The .NET Framework XML serialization infrastructure dynamically generates derivations of System.Xml.Serialization.XmlSerializer that are optimized to serialize user-defined types. The serializers are stored in assemblies that can be reused for efficient serialization.

The System.Xml.Serialization.XmlSerializerVersionAttribute attribute stores version information about the parent assembly for which a set of serializers is generated. Later, when the System.Xml.Serialization.XmlSerializer constructor is called, the infrastructure attempts to locate the pre-generated assembly. If the infrastructure finds an assembly with a matching name, the assembly is loaded and the infrastructure checks System.Xml.Serialization.XmlSerializerVersionAttribute for a match between the found assembly's version and the current version of the parent assembly. If the version does not match, the found assembly is not used. Instead, a temporary assembly is generated for the serialization.