/**
* Sets the dom tree and the css selector to compare against
* @param mixed $dom Dom tree to search into.
* @param mixed $selector Css selector to match element.
* @param string $message Customised message on failure.
* @access public
*/
function CssSelectorExpectation($dom, $selector, $message = '%s')
{
$this->SimpleExpectation($message);
$this->_dom = $dom;
$this->_selector = $selector;
$css_selector = new CssSelector($this->_dom);
$this->_value = $css_selector->getTexts($this->_selector);
}