In his More Color column at Macworld this week, Jason Snell writes about hidden features in Sierra.
This one regarding using Apple Pay on the Web—available only in Safari—caught my eye:
On stage, Federighi said that Apple Pay works with either an Apple Watch or an iPhone to let you buy stuff on the Web from right within Safari. What he didn’t mention is that since your Mac is aware if there’s an Apple-Pay eligible device within range, Safari can actually be instructed by web pages to show or hide Apple Pay buttons based on a device’s proximity to the Mac. That’s right, if you’re browsing an Apple Pay-enabled web site without your iPhone or Apple Watch nearby, a website can opt to make the Apple Pay button vanish. And then if you bring your iPhone within range, the Apple Pay button can magically reappear.