The format template interpetation engine.  See the comment at the
        beginning of this module for the how we interpret format
        specifications such as %c, %C, and so on.

def template_engine(self, entry, startnode):
        """The format template interpetation engine.  See the comment at the
        beginning of this module for the how we interpret format
        specifications such as %c, %C, and so on.
        """

        # print("-----")
        # print(startnode)
        # print(entry[0])
        # print('======')

        startnode_start = len(self.f.getvalue())
        start = startnode_start

        fmt = entry[0]
        arg = 1
        i = 0
        lastC = -1
        recurse_node = False

        m = escape.search(fmt)
        while m:
            i = m.end()
            self.write(m.group('prefix'))

            typ = m.group('type') or '{'
            node = startnode
            try:
                if m.group('child'):
                    node = node[int(m.group('child'))]
                    node.parent = startnode
            except:
                print(node.__dict__)
                raise

            if typ == '%':
                start = len(self.f.getvalue())
                self.write('%')
                self.set_pos_info(node, start, len(self.f.getvalue()))

            elif typ == '+': self.indent_more()
            elif typ == '-': self.indent_less()
            elif typ == '|': self.write(self.indent)
            # no longer used, since BUILD_TUPLE_n is pretty printed:
            elif typ == 'r': recurse_node = True
            elif typ == ',':
                if lastC == 1:
                    self.write(',')
            elif typ == 'b':
                finish = len(self.f.getvalue())
                self.set_pos_info(node[entry[arg]], start, finish)
                arg += 1
            elif typ == 'c':
                start = len(self.f.getvalue())

                index = entry[arg]
                if isinstance(index, tuple):
                    assert node[index[0]] == index[1], (
                        "at %s[%d], expected %s node; got %s" % (
                            node.kind, arg, node[index[0]].kind, index[1])
                        )
                    index = index[0]
                assert isinstance(index, int), (
                    "at %s[%d], %s should be int or tuple" % (
                        node.kind, arg, type(index)))
                self.preorder(node[index])

                finish = len(self.f.getvalue())
                self.set_pos_info(node, start, finish)
                arg += 1
            elif typ == 'p':
                p = self.prec
                (index, self.prec) = entry[arg]
                node[index].parent = node
                start = len(self.f.getvalue())
                self.preorder(node[index])
                self.set_pos_info(node, start, len(self.f.getvalue()))
                self.prec = p
                arg += 1
            elif typ == 'C':
                low, high, sep = entry[arg]
                lastC = remaining = len(node[low:high])
                start = len(self.f.getvalue())
                for subnode in node[low:high]:
                    self.preorder(subnode)
                    remaining -= 1
                    if remaining > 0:
                        self.write(sep)

                self.set_pos_info(node, start, len(self.f.getvalue()))
                arg += 1
            elif typ == 'D':
                low, high, sep = entry[arg]
                lastC = remaining = len(node[low:high])
                for subnode in node[low:high]:
                    remaining -= 1
                    if len(subnode) > 0:
                        self.preorder(subnode)
                        if remaining > 0:
                            self.write(sep)
                            pass
                        pass
                    pass
                arg += 1
            elif typ == 'x':
                src, dest = entry[arg]
                for d in dest:
                    self.set_pos_info_recurse(node[d], node[src].start, node[src].finish)
                    pass
                arg += 1
            elif typ == 'P':
                p = self.prec
                low, high, sep, self.prec = entry[arg]
                lastC = remaining = len(node[low:high])
                start = self.last_finish
                for subnode in node[low:high]:
                    self.preorder(subnode)
                    remaining -= 1
                    if remaining > 0:
                        self.write(sep)
                self.prec = p
                arg += 1

            elif typ == '{':
                d = node.__dict__
                expr = m.group('expr')

                # Line mapping stuff
                if (hasattr(node, 'linestart') and node.linestart
                    and hasattr(node, 'current_line_number')):
                    self.source_linemap[self.current_line_number] = node.linestart
                # Additional fragment-position stuff
                try:
                    start = len(self.f.getvalue())
                    self.write(eval(expr, d, d))
                    self.set_pos_info(node, start, len(self.f.getvalue()))
                except:
                    print(node)
                    raise
            m = escape.search(fmt, i)
            pass

        self.write(fmt[i:])
        fin = len(self.f.getvalue())
        if recurse_node:
            self.set_pos_info_recurse(startnode, startnode_start, fin)
        else:
            self.set_pos_info(startnode, startnode_start, fin)

        # FIXME rocky: figure out how to get these casess to be table driven.
        # 2. subroutine calls. It the last op is the call and for purposes of printing
        # we don't need to print anything special there. However it encompases the
        # entire string of the node fn(...)
        if startnode.kind == 'call':
            last_node = startnode[-1]
            self.set_pos_info(last_node, startnode_start, self.last_finish)
        return