A wildcard element represents an element which does not appear in the message model, but which could appear at the same position as the wildcard element in the input message.
Wildcard elements provide a means of adding flexibility to the message model, so that messages can be parsed even if they do not exactly match the message model.
Wildcard elements can only appear within a type or group with composition of sequence. If you want to allow unmodeled content to appear within a choice or all group, you must set the Content Validation to Open or Open Defined.