protected function processBlock($block) {
        foreach ($block->getContents() as $node) {
            if ($node instanceof AtRule) {

                $name = $node->atRuleName();
                if (isset(self::$atrules[$name])) {
                    foreach (self::$atrules[$name] as $prefix) {
                        $newname = $prefix . $name;
                        $newnode = clone $node;

                        if ($node instanceof KeyFrame) {
                            $newnode->setVendorKeyFrame($newname);
                            $block->insert($newnode, $node);

                        } else {
                            debugging('Unhandled atRule prefixing.', DEBUG_DEVELOPER);
                        }
                    }
                }
            }

            if ($node instanceof CSSList) {
                $this->processBlock($node);

            } else if ($node instanceof RuleSet) {
                $this->processDeclaration($node, $block);
            }
        }
    }