Having a stax source such as a streaming result from a web service that is processed by xmltable that contains comments will result in an exception such as:

14:39:23,673 ERROR [org.teiid.PROCESSOR] (Worker0_QueryProcessorQueue2) TEIID30019 Unexpected exception for request Wel3MG40y9Hs.0: java.lang.UnsupportedOperationException: append() method is not supported in this class
at net.sf.saxon.event.ProxyReceiver.append(ProxyReceiver.java:229) [saxonhe-9.2.1.5.jar:]
at net.sf.saxon.evpull.EventIteratorToReceiver.copy(EventIteratorToReceiver.java:50) [saxonhe-9.2.1.5.jar:]
at net.sf.saxon.event.Sender.sendPullEventSource(Sender.java:523) [saxonhe-9.2.1.5.jar:]
at net.sf.saxon.event.Sender.send(Sender.java:148) [saxonhe-9.2.1.5.jar:]
at net.sf.saxon.Configuration.buildDocument(Configuration.java:3317) [saxonhe-9.2.1.5.jar:]
at net.sf.saxon.Configuration.buildDocument(Configuration.java:3262) [saxonhe-9.2.1.5.jar:]
at org.teiid.query.xquery.saxon.XQueryEvaluator.evaluateXQuery(XQueryEvaluator.java:152) [teiid-engine-8.7.3.redhat-2.jar:8.7.3.redhat-2]