As of version 2.0, PHP/FI also supports this variation:
Notice that the end tag now consists of a question mark and a
greater-than character instead of just greater-than. However, if
you plan on using XML on your server, you will get problems with
the first new variant, because PHP may try to execute the XML
markup in XML documents as PHP code. Because of this, the
following variation was introduced:
Some people have had problems with editors that don't understand
the processing instruction tags at all. Microsoft FrontPage is
one such editor, and as a workaround for these, the following
variation was introduced as well: