Most of us (myself included) would probably see nothing wrong with the following XML processing instruction:
<?xml version="1.0" standalone="no" encoding="UTF-8"?>
Well, we'd be wrong! Although I have never seen it explicitly called out, the attributes of the XML processing instruction are order dependent and must appear in the following order:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
Of course, only the version attribute is required; encoding and standalone are optional.