private function _unset() {
    $statement_node = new UnsetStatementNode();
    $node = new UnsetNode();
    $this->mustMatch(T_UNSET, $node, 'name');
    $arguments = new CommaListNode();
    $this->mustMatch('(', $node, 'openParen');
    $node->addChild($arguments, 'arguments');
    do {
      $arguments->addChild($this->variable());
    } while ($this->tryMatch(',', $arguments));
    $this->mustMatch(')', $node, 'closeParen', FALSE);
    $statement_node->addChild($node, 'functionCall');
    $this->endStatement($statement_node);
    return $statement_node;
  }