Just when you thought Apple had browbeaten every app developer into submission, along comes a social network brazenly defying Apple’s “no porn” rule.

Actually, maybe not so brazenly. According to Tumblr, the recent app update that installed a “porn switch” in the iOS settings was implemented “per Apple’s content guidelines.”

The move likely will test the semantics of Apple’s developer guidelines, which state (emphasis at the end added):

To prevent abuse, apps with user-generated content or social networking services must include:

• A method for filtering objectionable material from being posted to the app
• A mechanism to report offensive content and timely responses to concerns
• The ability to block abusive users from the service
• Published contact information so users can easily reach you

Apps with user-generated content or services that end up being used primarily for pornographic content, objectification of real people (e.g. “hot-or-not” voting), making physical threats, or bullying do not belong on the App Store and may be removed without notice. If your app includes user-generated content from a web-based service, it may display incidental mature “NSFW” content, provided that the content is hidden by default and only displayed when the user turns it on via your website.

So how was Tumblr able to install an OS-level switch for its app? So far, neither Apple nor Tumblr have commented, but it’s been suggested that Tumblr may have jumped the gun on a planned change to parental control features in iOS 11, due to drop this summer.

If Tumblr’s app is allowed to remain in the App Store, Tumblr will have managed a coup — and perhaps that’s why Tumblr called out Apple in the app’s description. Tumblr is particularly susceptible to Apple’s censorship, considering the network is relatively heavy on porn thanks to its mostly hands-off policy regarding adult content. Although the network declines to host explicit videos, Tumblr advises users to embed the videos from another server.

SimilarWeb’s stats indicate the “adult” category is among the top direct traffic drivers for the site, accounting for more than 20 percent of clicks. The next two categories, “arts and entertainment” and “books and literature,” account for only 7.61 percent each.

Apple never has permitted apps whose sole purpose is to distribute pornography. The store is finicky even about accepting mainstream apps from known pornographers, although Pornhub recently got a kitschy mainstream app in, albeit under a pseudonym.

Social networks provide a unique challenge for censors, though. The networks are insanely popular, and users demand they be portable. For Apple to deny App Store space to Tumblr, Facebook, Twitter, Instagram and others very well might turn a significant number of iOS devotees away from a company that already is struggling to maintain market share against much-less-expensive and equally glittery Android devices.