_do_pi(self, node) -> None
        Process a PI node. Render a leading or trailing #xA if the
        document order of the PI is greater or lesser (respectively)
        than the document element.

def _do_pi(self, node):
        '''_do_pi(self, node) -> None
        Process a PI node. Render a leading or trailing #xA if the
        document order of the PI is greater or lesser (respectively)
        than the document element.
        '''
        if not _in_subset(self.subset, node): return
        W = self.write
        if self.documentOrder == _GreaterElement: W('\n')
        W('<?')
        W(node.nodeName)
        s = node.data
        if s:
            W(' ')
            W(s)
        W('?>')
        if self.documentOrder == _LesserElement: W('\n')