How to get sharing source similar to Reminders share extension?

In Mail or Safari, user can select text to bring up the edit menu..

When sharing the text selection to Reminders using Share Extension, Reminders App's share extension is able to identify the "source" and show the app icon linking back to the original web page or email. (Please check attached screenshots)

In my own Share Extension, how do I get, say, an URL object linking to the sharing source?

I've looked at NSExtentionContext, NSExtensionItem and NSItemProvider documentation. It doesn't look like there's a public interface to retrieve that info.

Do u guys have any suggestion?

Thanks Bill