public boolean isStartOfDocument() throws XMLStreamException {
        return eventReader.peek().isStartDocument();
    }
Returns true if this unmarshaller context is at the very beginning of a
source document (i.e. no data has been parsed from the document yet).

@return true if this unmarshaller context is at the very beginning of a
        source document (i.e. no data has been parsed from the document
        yet).
aws-java-sdk-core/src/main/java/com/amazonaws/transform/StaxUnmarshallerContext.java