private function _global() {
    $node = new GlobalStatementNode();
    $this->mustMatch(T_GLOBAL, $node);
    $variables = new CommaListNode();
    do {
      $variables->addChild($this->globalVar());
    } while ($this->tryMatch(',', $variables));
    $node->addChild($variables, 'variables');
    $this->endStatement($node);
    return $node;
  }