Apple's new Handoff feature in iOS 8 and OS X Yosemite not only lets users pick up on one app from where they left off on another, but it can "forward" them to a website on an iPhone, iPad or Mac, according to Apple's documentation.

Handoff, part of "Continuity," a term Apple's used to describe several features of iOS and OS X, allows users to begin an activity -- writing an email, browsing the Web, creating a document -- and then resume it on another device.

The feature relies on proximity awareness -- powered by Bluetooth -- on Apple hardware to recognize devices registered to the same iCloud account. Once that ad hoc pairing takes place, users can hand off in-progress tasks. Apple will support Handoff on many of its own iOS apps and OS X applications bundled with iOS 8 and Yosemite, including the iWork troika -- Pages, Numbers and Keynote -- Contacts, Mail, Maps, Notes, Reminders and the Safari browser.

But it will also open up Handoff to third-party developers via several APIs (application programming interfaces), giving them a chance to add the feature to their own wares.

Although Apple demonstrated the feature last week using its software, developers can bake Handoff "awareness" into their apps and applications. For example, someone who started a document on the iPad version of the Byword text editor could finish it on the OS X application, assuming the program's developer added Handoff support.

But not every iOS or OS X app has a corresponding sibling. There may be an OS X version, but not one for mobile, or one for the iPhone but not for the Mac.

"There can be a situation where the user is using a native application on the originating device, and the user wants to continue the activity on another device that does not have a corresponding native application, but there is a Web page corresponding to the activity," Apple stated on one page of its preliminary Handoff developer documentation.

In that case, developers can create links between an iOS or OS X app, and the developer's website. For example, Feedly, the RSS service that supplanted Google Reader last year, has an iOS app but not a native application on OS X. For the latter, a browser-based interface -- slick though it is -- is all that's available.

Feedly could provide Handoff support in its iOS app; users would be able to pick up where they left off on the Feedly UI (user interface) on the Mac within Safari.

According to public documentation for Handoff -- and a 50-minute WWDC session that was recorded and is available for playback -- Feedly's engineers would have to prove that they own the domain they will pass from their iOS app to Safari. Browser developers may also direct the in-progress command sent from an app so that a non-Apple browser opens rather than Safari, assuming the user has set the other browser as their default.

Google, for instance, could direct that a handoff from its iOS app for Gmail opens in Chrome, not Safari on a Mac, if the user had installed Chrome and set it as their default browser.

The opposite direction, browser-to-native-app, is also supported by Handoff.

Even software developers with corresponding apps on both iOS and OS X can implement app-to-browser and browser-to-app Handoff to cover cases when the user has just one of the apps, say on iOS, but has not paid for, downloaded and installed the partnered OS X application.

Data representing Handoff activities will be sent via Bluetooth from one device to another, so Bluetooth must be enabled on both ends of the conversation for the feature to work.

Both iOS 8 and OS X Yosemite will be free upgrades, and while Apple has not firmed up a delivery date, it said last week that the two would be available this fall.

Developers can bake 'Handoff' into their native iOS apps, but then let users resume tasks in a browser-based UI on OS X Yosemite. (Image: Apple.)

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is gkeizer@computerworld.com.

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