Apple CEO Tim Cook. Getty Images/Stephen Lam It looks as if Apple is about to allow its users to block ads from their iPhones and iPads.

As Nieman Lab reports, Apple's developer documentation detailing "What's New in Safari" (Apple's internet browser) highlights the change. The document (which you find read in full here) reads: "The new Safari release brings Content Blocking Safari Extensions to iOS. Content Blocking gives your extensions a fast and efficient way to block cookies, images, resources, pop-ups, and other content."

Business Insider has contacted Apple for clarification as to whether this means it will allow developers to build ad-blocking apps and browser extensions. We'll update this article once we hear back. But sources within the ad-blocking community, and other news outlets such as the Financial Times and The Next Web, have interpreted the update to mean Apple will allow users to block ads in some form.

That would be a huge blow for online publishers, many of whom rely on advertising for most of their revenue, and to create content that readers can consume for free.

Apple allowing ad blocking would further push the technology into the mainstream. The number of people with ad blockers installed worldwide grew 70% year-on-year to 144 million in 2014 and is expected to rise another 50% this year, according to PageFair and Adobe.

There is the argument that, because it looks as if Apple will allow ad blocking only as an opt-in (i.e., people will have to choose to download a browser extension such as Adblock Plus), it is only the existing ad-blocking crowd that will get on board with ad blocking on iPhones and iPads. But that's still worrisome for publishers, most of which now report that more than 50% of their audiences come from mobile — and iPhone and iPad users are generally seen as the most valuable of the lot.

Previously, ad-blocking companies have found it difficult to build for mobile. One of the reasons one of the most popular ad blockers, Adblock Plus, recently created its own Android browser is because its previous Android browser extension was removed by Google from the Play Store (Google's app store) for violating rules on interfering with other apps' functionality. And Adblock Plus operations and communications manager Ben Williams told Business Insider last month that iOS had been "harder to develop on," describing it as a "walled garden that's more difficult to get an API." Not so anymore, it seems.

Apple CEO Tim Cook has recently launched attacks against Silicon Valley technology companies that collect data about users to serve them ads. In a speech earlier this month, Cook — fairly obviously taking a swipe at Facebook and Google — said:

Our privacy is being attacked on multiple fronts. I'm speaking to you from Silicon Valley, where some of the most prominent and successful companies have built their businesses by lulling their customers into complacency about their personal information. They're gobbling up everything they can learn about you and trying to monetize it. We think that's wrong. And it's not the kind of company that Apple wants to be.

Cook, however, has been accused of being "disingenuous" in this argument. Apple itself has a division that is in the business of serving ads: iAd. True, it's a tiny part of the company's business, generating just $487 million last year, or 0.3% of Apple's total revenue, according to eMarketer.

But it could be about to become a lot more important to Apple. At its big developers conference earlier this week, Apple announced a Flipboard-style News app as part of the iOS9 update that's coming later this year. Publishers including The New York Times, Wired, and ESPN have signed up as launch partners.

Publishers can choose to earn 100% of the revenue from the ads they sell, or 70% if Apple's iAd sells the ads for them. As Nieman Lab points out, all but the biggest publishers will most likely rely on Apple to do the ad selling on their behalf.

A cynic could infer that by allowing ad blocking Apple is hoping it can shift news and magazine consumption away from the browser and directly into its app, where it has a chance of monetizing the content. Or even away from the mobile web and to publishers' own news apps, which arguably offer a better experience than the browser. It's a stretch — most people don't necessarily fire up a news app each morning; they get their content from Facebook, Twitter, search, WhatsApp and so on — but until Apple provides further clarification on exactly what its "content blocking Safari extensions" have actually been designed for, publishers are on high alert.