I don't disagree with you, I didn't get what you mean by "XML error" and I'm afraid I still don't get it. If you mean that with "missing attributes" you can still parse the file because it remains "well formed" I agree. A XML parser can parse any wellformed XML document, otherwise it would not be compliant. Missing attributes won't make a difference.
In order for a XML document to be wellformed you need at least a root element though. What got me on the wrong foot is that the OP mentions he knows what attributes to expect, I sort of assumed he has schema(s) and/or DTD(s) and therefore a validating parser. Validation is optional of course.