SCE — XSD copied the wrong extension elements from BPMN and lacks the important ones

SCE copied extension classes from BPMN that were meant for extensibility of the metamodel and are explicitly declared to not show in the XML schema because the XML already has built-in extension mechanisms. That's what the X in XML stands for

The XSD is missing the extensionElements container that BPMN, CMMN & DMN are using to store XML extension elements in a way that schema validation is not ambigious.

The SCE XSD even includes the statements that BPMN made about these classes, e.g.:

ExtensionDefinition: This type is not applicable when the XML schema interchange is used, since XSD Complex Types already satisfy this requirement.

ExtensionAttributeDefinition/ExtensionAttributeValue: This type is not applicable when the XML schema interchange is used; since the XSD mechanisms for supporting "AnyAttribute" and "Any" type already satisfy this requirement.

extensionDefinitionRef/extensionAttributeValueRef: This association is not applicable when the XML schema interchange is used, since the XSD mechanisms for supporting anyAttribute and any element already satisfy this requirement.

BPMN had the classes ExtensionDefinition, ExtensionAttributeDefinition, ExtensionAttributeValue only in the UML metamodel but not in the XML schema. During the RFP phase, SCE had already removed the classes from its UML metamodel and specification text because UML also has built-in extension mechanisms. However, it seems like they were automatically generated into the XML schema and are still in there.

In addition, the XSD also contains Adornment types that are based on the extension type, which should have not been in the XSD.