docs: def _parse(self):
          """ Performs parsing process against token stream to generate the
              internal abstract syntax tree (AST) for general purpose use.
  
              * Raises a ``ParseError`` exception upon failure.
              """
          try:
              # parse token stream into abstract syntax tree (AST)
              self._ast = self._rule_container()
  
          except ParseError:
              raise
  
          except Exception as exc:
              raise ParseError(u'Unexpected error: {0}'.format(unicode(exc)))