Snapchat also hopes to make Discover more kid-friendly. A tool arriving in February will let publishers set age gates for content, and in some cases block underage users from seeing content in the first place. This wouldn't prevent determined teens from looking at racy or graphic stories, but it would reassure nervous parents -- not to mention advertisers worried that their promos might run alongside salacious material.

The stricter guidelines say a lot about Snapchat's long-term plans for Discover. It's determined to treat the service much like TV, and that means both raising expectations and filtering what you see. Yes, it means that Discover will be a tamer place than before, but look at it this way -- Twitter is struggling in part because it's having trouble with trolls and other nasty content. The Snapchat crew likely doesn't want to risk a similar outcome.

The rules are coming at an appropriate time, too. Snapchat is now rolling out its updated design to everyone, not just a handful of Android users. As before, the centerpiece is a universal search that helps you find whatever you're looking for, whether it's a friend to chat with or a Discover story. You'll also see an overall visual upgrade and a greater emphasis on Bitmoji avatars. The software improvements will definitely be the most noticeable thing you'll see today, but don't be surprised if the Discover guidelines make a greater impact in the long run.