'Pop a nonterminal.  (Internal)'

def _pop(self):

    (popdfa, popstate, (type_, children)) = self.stack.pop()
    if (len(children) == 1):
        newnode = children[0]
    else:
        newnode = self.convert_node(self.grammar, type_, children)
    try:
        self.stack[(-1)][2][1].append(newnode)
    except IndexError:
        self.rootnode = newnode
