'A stub version of ``_parse`` that sets the parsers current
state to the given arguments.  In ``RecursiveDescentParser``,
the ``_parse`` method is used to recursively continue parsing a
text.  ``SteppingRecursiveDescentParser`` overrides it to
capture these recursive calls.  It records the parser\'s old
state in the history (to allow for backtracking), and updates
the parser\'s new state using the given arguments.  Finally, it
returns ``[1]``, which is used by ``match`` and ``expand`` to
detect whether their operations were successful.
:return: ``[1]``
:rtype: list of int'

def _parse(self, remaining_text, tree, frontier):

    self._history.append((self._rtext, self._tree, self._frontier))
    self._rtext = remaining_text
    self._tree = tree
    self._frontier = frontier
    if ((len(frontier) == 0) and (len(remaining_text) == 0)):
        self._parses.append(tree)
        self._trace_succeed(self._tree, self._frontier)
    return [1]
