Apple brings ad-blocker extensions to Safari on iPhones
Faster iPhones and a new TV box are likely to dominate Apple's launch event on Wednesday, but a tweak to the firm's mobile web browser will arguably be just as far-reaching.
For the first time, Apple will allow adverts to be blocked by the iPhone and iPad versions of Safari.
The move is likely to please users, but will concern the many companies that depend on advertising.
What is an ad-blocker?
In a nutshell, the term covers a variety of technologies used to prevent adverts appearing on internet-connected devices.
They are already widely used on PCs, where the most common technique is to install a browser plug-in, but are relatively rare on smartphones and tablets.
That's not to say it's impossible to use them on mobile kit.
Apple and Android devices can already run specialised third-party ad-blocking browsers or be made to stop ads appearing by altering their network settings, but the point is that only a small percentage of people do this.
Apple's decision to open up Safari, however, could take the activity mainstream.
What's the benefit to users?
Webpages should be decluttered of distracting content.
Pages should also load more quickly, mobile data allowances should come under less strain and iPhone batteries could also last longer between charges.
So, what exactly is Apple doing?
Apple's iOS 9 operating system will allow content blocking extensions to be added to Safari.
These browser add-ons can be set to block certain cookies, images, pop-ups and other content from being downloaded.
Until now, the only way to do something similar was to "jailbreak" the handsets, which also made them more vulnerable to malware.
Apple will not offer its own ad-blocking software.
Instead, people will be able to download extensions made by others from its App Store in a similar way to how they can already install third-party keyboards.
How will the extensions work?
By detecting and stripping out scripts in the code of web pages meant to make browsers pull content from ad networks' computer servers.
They will also act to prevent scripts from doing things like tracking how long a user has been looking at a webpage and monitoring how far they have scrolled down a page in order to serve up more ads.
Presumably this is going to worry those who rely on ads to make money?
Absolutely. There have already been loud complaints about the spread of ad-blockers on PCs and several of Germany's leading publishers have tried and failed to block their spread via the courts.
Their fear is that the practice could now become widespread on mobile.
About 198 million people - representing roughly one in 20 internet users - already use ad-blockers on desktop computers, according to a recent study by Pagefair, a company that sells a workaround to the extensions.
iPhones and iPads may be outsold by Android devices, but they represent "52% of the mobile browsing market and 14% of total web browsing", its report states, adding that Apple's move could be a "game changer".
The Interactive Advertising Bureau (IAB) trade association also warns that the consequences could be calamitous for some sites.
"If you are a medium or small-sized website operating on very tight margins, this could make or break the business," suggests Stephen Chester.
"Particularly news organisations - whose revenues are under fire at the moment as their print circulations diminish but online audiences grow. Those organisations are having to reshape to adapt to the digital world and ultimately this could break them or put them at risk."
So, will no ads get through at all?
Cologne-based Eyeo makes Adblock Plus, a free PC plug-in that is the most popular of its kind.
It operates a "white list" of adverts that are still permitted to appear. Such ads must meet certain criteria - for instance they cannot be pop-ups or automatically start playing sounds.
Google, Amazon and Microsoft are among those reported to have paid the firm for "support services" to ensure ads on their sites get through.
Eyeo says it is "confident that our years of experience" will help it compete against others when it brings the service to iOS 9.
But one rival is hoping to prosper by taking a more open approach.
Teesside-based developer Dean Murphy plans to sell the extension Crystal for about £3 and let its users create and maintain their own white lists.
"A lot of websites I love rely on ad revenue, but at the back of my mind I just think advertising needs to change," he explains.
"There's so many terrible ads out there that auto-load videos, and show lots of images and lots of banners.
"And there's often multiple ad networks being used on a single page.
"I tested 10 popular news websites. With Crystal enabled they loaded four times quicker and used half the amount of data."
Of course, marketers try to make adverts obtrusive for a reason - they are more likely to be noticed.
Wait a second. Apple runs its own ad platform. Won't this hurt that business?
No - it might have the opposite effect.
Apple's iAd service places adverts in apps rather than websites, so won't be affected by the extensions.
In fact, the facility gets a boost in iOS 9 because of its use in a new News app where it will be used to place adverts alongside publishers' articles in curated topic feeds.
Rival app-based platforms - including MoPub and Google's AdMob - as well as social networks that sell space in their own apps - such as Facebook and Twitter - could also scoop up more business.
But Google's hugely profitable website-based AdSense business will be hit. How's it taking this?
You might be surprised to hear the firm's view isn't all that different from the ad-blockers themselves.
"The industry needs to do better at producing ads that are less annoying and that are quicker to load," said chief executive Larry Page at a recent shareholders meeting.
"I think we need to do a better job of that as an industry."
It's worth being aware, however, that a recent study by the IAB indicated that the majority of people who had installed ad-blocking extensions on PCs did so because they wanted to be free of all ads, not just certain ones.
Isn't there a start-up planning a wider-reaching ad blocker?
Right. Israel-based Shine says it can block ads from appearing in both apps and mobile websites on all handsets.
However, the technology is targeted at mobile operators, rather than consumers, who must add the start-up's software to their data centres.
The firm launched a publicity campaign for its innovation on Monday, somewhat ironically, by placing an ad in the Financial Times.