Attribute encoders convert the internal representation of an IdPAttribute into a particular protocol format. The supported encoders currently support SAML 1, SAML 2, and CAS representations. The mechanism is inherently limited to XML-based output formats.
Attribute encoders are specified with the xsi:type attribute within the <AttributeEncoder> element.
General purpose attribute encoding is best achieved by using the Attribute Registry. Explicit per-attribute encoding continues to be useful when you want to associate an ActivationCondition with the encoder (though this is also possible via rules in the registry).
Note that a source of confusion is that because of the changes to how this code operates, when you add or remove encoders to your resolver configuration, the changes won't take effect until/unless the AttributeRegistryConfiguration is reloaded.