I haven't seen this linked before – and I certainly didn't see it when I first wrote about iOS 9 search – but Apple has a new validation tool to test websites for App Search, coming with iOS 9 in Spotlight.
Test your webpage for iOS 9 Search APIs. Enter a URL and Applebot will crawl your webpage and show how you can optimize for best results.
As I wrote, iOS 9 won't be limited to searching for local app content:
To enhance web crawling with structured data and, again, give developers control of indexed content, Apple has announced support for various types of web markup. Developers who own websites with content related to an app will be able to use Smart App Banners to describe deep links to an app (more on this in a bit) as well as open standards such as schema.org and Open Graph.
Apple calls these “rich results”: by reading metadata based on existing standards, Apple's web crawler can have a better understanding of key information called out on a webpage and do more than simply parsing a title and a link. With support for schema.org, for instance, Applebot will be able to recognize tagged prices, ratings, and currencies for individual listings on Airbnb, while the Open Graph image tag could be used as the image thumbnail in iOS search results. An app like Songkick could implement structured data to tag concert dates and prices in their related website, and popular concerts could show up for users with rich descriptions in the iOS 9 search page.
The validation tool does indeed analyze information that will be used to power iOS 9 search results – such as thumbnails, descriptions, and deep links to apps. You can try it out here.