e.g. to ensure that
<meta name="robots" content="noindex" />
does not exists on the page.
$I->wantTo('Check that page can be indexed');
$I->amOnPage('/');
$I->dontSeeInPageSource('<meta name="robots" content="noindex" />');
but it returns the error
Call to undefined method WebGuy::dontSeeInPageSource
$I->dontSeeElement('meta[name=robots]');