browser.php
protected function load($url, $parameters)
    {
        $frame = $url->getTarget();
        if (! $frame || ! $this->page->hasFrames() || (strtolower($frame) == '_top')) {
            return $this->loadPage($url, $parameters);
        }

        return $this->loadFrame(array($frame), $url, $parameters);
    }
protected function load($url, $parameters)
    {
        $frame = $url->getTarget();
        if (! $frame || ! $this->page->hasFrames() || (strtolower($frame) == '_top')) {
            return $this->loadPage($url, $parameters);
        }

        return $this->loadFrame(array($frame), $url, $parameters);
    }
Fetches a page or a single frame if that is the current focus.

@param SimpleUrl $url                   Target to fetch.
@param SimpleEncoding $parameters       GET/POST parameters.

@return string                          Raw content of page.