The default StAX parser does not produce the correct events when the input document is:

<?xml-stylesheet href="bar.xsl" type="text/xsl"?>
<foo/>

In this case, the XMLStreamReader (com.sun.xml.internal.stream.XMLInputFactoryImpl) starts on a PROCESSING_INSTRUCTION event.  Instead, it should start on a START_DOCUMENT event.

 From JSR 173, 1.0, Section 5.1, XMLStreamReader:
"At any moment in time an XMLStreamReader instance has a current event that the methods of the interface access. Instances are created in the START_DOCUMENT state and this is set to the current event type."

Here is a reproducer:

---------- BEGIN SOURCE ----------
import java.io.StringReader;

import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamReader;

public class TestStAX {

   public static void main(String[] args) throws Exception {
       String xml = "<?xml-stylesheet href=\"bar.xsl\" type=\"text/xsl\"?>" +
                    "<foo/>";
       XMLInputFactory factory = XMLInputFactory.newFactory();

       // class com.sun.xml.internal.stream.XMLInputFactoryImpl
       System.err.println(factory.getClass());
       XMLStreamReader reader = factory.createXMLStreamReader(new StringReader(xml));

       // prints false, should print true
       System.err.println(reader.getEventType() == XMLStreamConstants.START_DOCUMENT);

       // prints true, should print false
       System.err.println(reader.getEventType() == XMLStreamConstants.PROCESSING_INSTRUCTION);

       // From JSR 173, 1.0, Section 5.1, XMLStreamReader:
       //  "At any moment in time an XMLStreamReader instance has a current event that the
       //   methods of the interface access. Instances are created in the START_DOCUMENT
       //   state and this is set to the current event type."
   }

}
---------- END SOURCE ----------