Comment 2 for bug 1708138

The link in the Wikipedia article (http://www.is-thought.co.uk/book/sgml-8.htm#PI) is a 404. But https://www.w3.org/TR/NOTE-sgml-xml seems to indicate that the PI terminators in XML and SGML are indeed different. However this would mean that the _ProcessingInstruction object might have to remember whether it is an XML or an SGML PI?