XmlSchemaChoice.getItems() should probably return XmlSchemaChoiceMember instead of XmlSchemaObject.

XmlSchemaSequence.getItems() returns XmlSchemaSequenceMember. IMHO XmlSchemaChoice.getItems() should return XmlSchemaChoiceMember.
Also XmlSchemaChoiceMember could inherit XmlSchemaObjectBase (as XmlSchemaSequenceMember does), so both XmlSchemaSequence.getItems() and XmlSchemaChoice.getItems() will return XmlSchemaObjectBase type that facilitates parsing.