static function evaluate($xpath)
{
if (!self::$xml) {
self::$xml = new DOMDocument();
self::$xpath = new DOMXPath(self::$xml);
}
return self::$xpath->evaluate($xpath);
}
private function group($name, $args)
{
$mangled = xpression::mangle($name, $args);
isset($this->groups[$mangled]) or runtime_error('Group not found: ' . $mangled);
return $this->groups[$mangled];
}
