Infrequently Noted

Recent posts here covering the slow pace of WebKit development and ways the mobile browser market has evolved to disrespect user choice have sparked conversations with friends and colleagues. Many discussions have focused on Apple's rationales, explicit and implied, in keeping the iOS versions of Edge, Firefox, Opera, and Chrome less capable than they are on every other platform.

How does Apple justify such a policy? Particularly since last winter, when it finally (albeit haltingly and eventually) became possible to set a browser other than Safari as the default?

Two categories of argument are worth highlighting: those offered by Apple and claims made by others in Apple's defence^[1].

Apple's Arguments #

The decision to ban competing browser engines is as old as iOS, but Apple has only attempted to explain itself in recent years. I'm only aware of a few such instances:

• Apple's 2019 response to the U.S. House Judiciary Committee's Subcommittee on Antitrust, Commercial and Administrative Law (PDF)
• Apple's February 2021 response to the Australian Competition & Consumer Commission (PDF)
• 2021 court arguments in the case of EPIC Games vs. Apple (slide image)

Experts tend to treat Apple's arguments with disdain, but understanding why isn't instantly apparent to a non-technical audience. Apple's response to the U.S. House Antitrust Subcommittee includes their most specific responses to the set of claims:

4. Does Apple restrict, in any way, the ability of competing web browsers to deploy their own web browsing engines when running on Apple's operating system? If yes, please describe any restrictions that Apple imposes and all the reasons for doing so. If no, please explain why not.

All iOS apps that browse the web are required to use "the appropriate WebKit framework and WebKit Javascript" pursuant to Section 2.5.6 of the App Store Review Guidelines <https://developer.apple.com/app-store/review/guidelines/#software-requirements>.

The purpose of this rule is to protect user privacy and security. Nefarious websites have analysed other web browser engines and found flaws that have not been disclosed, and exploit those flaws when a user goes to a particular website to silently violate user privacy or security. This presents an acute danger to users, considering the vast amount of private and sensitive data that is typically accessed on a mobile device.

By requiring apps to use WebKit, Apple can rapidly and accurately address exploits across our entire user base and most effectively secure their privacy and security. Also, allowing other web browser engines could put users at risk if developers abandon their apps or fail to address a security flaw quickly. By requiring use of WebKit, Apple can provide security updates to all our users quickly and accurately, no matter which browser they decide to download from the App Store.

WebKit is an open-source web engine that allows Apple to enable improvements contributed by third parties. Instead of having to supply an entirely separate browser engine (with the significant privacy and security issues this creates), third parties can contribute relevant changes to the WebKit project for incorporation into the WebKit engine.

It's worth assessing these claims from most easily falsified to most contested.

Apple's Open Source Claim #

The open source nature of WebKit is indisputable as a legal technicality. Anyone who cares to download and fork the code can do so. To the extent they are both skilled in browser construction and endowed with the freedom to distribute binaries with modifications, the WebKit project can serve as the basis for modified engines of all sorts, fulfilling the chief rights and liberties guaranteed by open source licensing.

Apple, however, goes further in this claim, asserting that the open source nature of the WebKit project extends to open governance regarding feature additions. Apple must know this is misleading.

Presumably, Apple's counsel included this specious filigree to distract from the reality that half of the conditions necessary for driving progress through open source are foreclosed by iOS policies preventing browsers from shipping their own engines.

Anyone can modify WebKit, but the chances of Apple actually accepting changes to their engine are, historically, relatively low — and here I speak from experience.

From 2008 to 2013, the Chrome project was based on WebKit, and a growing team of Chrome engineers began to contribute heavily "upstream." The eventual Blink fork was precipitated by an insurmountable difficulty in doing precisely what Apple suggested to Congress: contributing code upstream to WebKit to enable new features.

Far from being straightforward, the differing near-term objectives of browser teams ensure that potential additions are contentious. Project owners are territorial, fiercely guarding the integrity of their codebases. Until and unless they become convinced of the utility of a feature, "no" is the usual response.

Large projects like browser engines also exercise governance through a hierarchy of "OWNER bits," which explicitly name engineers empowered to permit changes in a section of the codebase. There tend to be very few experts in each area versus the number of engineers attempting to contribute code, and sign-off of an OWNER is frequently required before the project accepts changes.

For example, OWNERs and experts in video and audio codecs can agree to extensive changes in their domain but cannot green-light changes in areas such as layout, networking, storage, or JavaScript engines. The collaboration required to approve changes in an area can quickly look like a drain or tax on scarce resources better spent elsewhere, at least from the perspective of a company employing these very senior engineers. If the organisation finds its most senior engineers are spending a great deal of time reviewing code for features they have no interest in — and may "flag off" in their own products^[2] — it becomes inevitable that managers will communicate disinterest. The pace of reviews needed to finish a feature in this state can taper off or dry up completely, frustrating collaborators on both sides.

This was exactly the experience of Chrome while developing Web Components.

When browsers provide integrated engines (an "integrated browser"), then it's possible to disagree in standards venues, return to one's corner, and deliver (hopefully and responsibly) the best design to developers. Developers can provide feedback from using features and lobby other browsers to adopt (or re-design) them. This process can be messy and slow, but it never creates a political blockage for developing new capabilities for the web.

WebKit, by contrast, has in recent years gone so far as to publicly state that they pre-emptively "decline to implement" a veritable truckload of useful new features that some browser vendors feel are essential to the future of productivity on the web.

The signal to parties who might contribute code for these features could scarcely be clearer: your patch is unlikely to be accepted.

Suppose by some miracle a "controversial" feature is merged into WebKit. Such features have lingered behind feature flags for years, never to be flagged on by default in Safari or even made available to competing iOS browsers.

When priority disagreements inevitably arise, alternative iOS browsers cannot even demonstrate through contributions to WebKit that a feature is safe or well received by web developers on iOS. Potential contributors won't dare the expense of an attempt. Apple's opacity and history of challenging collaboration have done more than enough to discourage adventurous developers.

Other mechanisms for extending features of third party browsers may be possible (and in some areas, with low fidelity on iOS; more on that below), but contributions to WebKit are not a viable path for a majority of potential additions.

It is both shocking and unsurprising that Apple felt compelled to mislead Congress on these points, given the facts are not in their favour and few legislative staffers have enough context to see through a browser internals smoke screen.

Apple's Security Argument #

The most convincing argument in Apple's 2019 response to the U.S. House Judiciary Committee is rooted in security. Apple argues it bans other engines from iOS because:

Nefarious websites have analysed other web browser engines and found flaws that have not been disclosed, and exploit those flaws when a user goes to a particular website to silently violate user privacy or security.

Like all browsers, WebKit and Safari are under constant attack, including the construction of "zero day" attacks that Apple insinuates WebKit is immune to.

As a result of this threat landscape, responsible browser vendors work to put untrusted code (everything downloaded from the web) in "sandboxes"; restricted execution environments that are given fewer privileges than regular programs. Modern browsers layer protections on top of OS-level sandboxes, bolstering the default configuration with further limits on "renderer" processes.

Some engines go further, adopting safer systems languages in their first lines of defence, or using a larger number of sandboxes to strictly isolate individual websites from each other. Thanks to Apple's policy, none of these protections were in place for iOS users in the most recent Solar Winds incident, not even folks who use browsers other than Safari. The beefy devices Apple sells provide more than enough resources to raise such software defences, yet iOS users are years behind for no other reason than Apple's own under-investment in — and disinterest about letting others deliver — better security.

Leading browsers are also adopting more robust processes for closing the "patch gap". Since all engines — even the ones given the most care — contain latent security bugs, precautions to insulate users from partial failure (e.g., sandboxing), and the velocity with which fixes reach end-user devices are paramount in determining the security posture of modern browsers. Apple's rather larger patch gap serves as an argument in favour of engine choice, all things equal. Apple's industry-lagging delays are hardly confidence inspiring.

This brings us to the final link in the chain of structural security mitigations: the speed of delivering updates to end-users. Issues being fixed in the source code of an engine's project has no impact on its own; only when those fixes are rolled into new binaries and those binaries are delivered to user's devices do patches become fixes.

Apple's reply hints at the way its model for delivering fixes differs from all of its competitors:

[...] By requiring apps to use WebKit, Apple can rapidly and accurately address exploits across our entire user base and most effectively secure their privacy and security.

[...]

By requiring use of WebKit, Apple can provide security updates to all our users quickly and accurately, no matter which browser they decide to download from the App Store.

Aside from Chrome on Chrome OS (and not for much longer), I'm aware of no modern browser that continues the medieval practice of requiring users download and install updates to their Operating System to apply browser patches. Lest the Chrome OS situation seem like a defence of the iOS position, it's not; the cost to end-users of these updates in terms of time and effort is night-and-day, thanks to near-instant, transparent updates on restart. If only my (significantly faster) iOS devices updated this transparently and quickly!

All other browsers update "out of band" from the OS, including the WebView system component on Android. The result is, that for users endowed with equivalent connectivity and disk space, out-of-band patches are installed on the devices significantly faster.

This makes intuitive sense: iOS updates are often very large and can disrupt of a device for as much as a half an hour. Users understandably hesitate at these sorts of interruptions. Browser updates delivered out-of-band can be smaller and faster to apply, often without any explicit user intervention. In many cases, simply restarting the browser delivers improved security updates.

Differences in uptake rates matter because it's only by updating a program on the user's devices that fixes can begin to protect users. iOS's high friction engine updates are a double strike against its security posture; albeit ones Cupertino has attempted to spin as a positive.

The philosophical differences underlying software update mechanisms run deep. All other projects have learned through long experience to treat operating systems as soft targets that must be defended by the browser, rather than as the ultimate source of user defence. To the extent that the OS is trustworthy, that's a "nice to have" property that can add additional protection, but it is not treated as a fundamental protection in and of itself. Browser engineers outside the WebKit and Safari projects are habituated to thinking of OS components as systems not designed for handling unsafe third-party input. Mediating layers are therefore built to insulate the OS from malicious sites.

Apple, by contrast, tends to rely on OS components directly, leaning on fixes within the OS to repair issues which other projects can patch at a higher level. Apple's insistence on treating the OS as a single, hermetic unit slows the pace of fixes reaching users, and results in reduced flexibility in delivering features to web developers. While iOS has decent baseline protections, being unable to layer on extra levels of security is a poor trade.

This arrangement is, however, maximally efficient in terms of staffing, as it means less expertise is duplicated across teams, requiring fewer engineers. But is HR cost efficiency for Apple the most important feature of a web engine? And shouldn't users be able to choose engines that are willing to spend more on engineering to prevent latent OS issues from becoming security problems? By maintaining a thin artifice of perfect security, Apple's iOS monoculture renders itself brittle in the face of new threats, leaving users without the benefits of the layered paranoia that the most secure browsers running on the best OSes can provide.^[3] As we'll see in a moment, Apple's claim to keep users safe when using alternative browsers by fusing engine updates to the OS is, at best, contested.

Instead of raising the security floor, Apple has set a cap while breeding a monoculture that ensures all iOS browsers are vulnerable to identical attacks, no matter whose icon is on the home screen.

Introducing Apple to developer.apple.com #

Given Apple's response to Congress, it seems Cupertino is unfamiliar with the way iOS browsers other than Safari are constructed. Because it forbids integrated browsers, developers have no choice but to use Apple's own APIs to construct message-passing mechanisms between the privileged Browser Process and Renderer Processes sandboxed by Apple's WebKit framework.

These message-passing systems make it possible for WebKit-based browsers to add a limited subset of new features, even within the confines of Apple's WebKit binary. With this freedom comes the exact sort of liabilities that Apple insists it protects users from by fixing the full set of features firmly at the trailing edge.

To drive the point home: alternative browsers can include security issues every bit as severe as those Apple nominally guards against because of the side-channels provided by Apple's own WebKit framework. Any capability or data entrusted to the browser process can, in theory, be put at risk by extensions. Even more worrisome is that these extensions are built in a way that is different to the mechanisms used by browser teams on every other platform. This means that any browser that delivers a feature on every other platform, then tries to bring it to iOS through script extensions, has now doubled the security analysis surface area. None of this is theoretical; needing to re-develop features through a straw, using less-secure and more poorly tested and analyzed mechanisms, has led to serious security issues in alternative iOS browsers over the years. Apple's policy, far from insulating responsible WebKit browsers from security issues, is a veritable bug farm for the projects wrenched between the impoverished feature set of WebKit and the features they can securely deliver with high fidelity on every other platform.

This is, of course, a serious problem for Apple's argument as to why it should be exclusively responsible for delivering updates to browser engines on iOS.

The Abandonware Problem #

Apple cautions against poor browser vendor behaviour in its response, and it deserves special mention:

[...] Also, allowing other web browser engines could put users at risk if developers abandon their apps or fail to address a security flaw quickly.

Ignoring the extent to which WebKit represents precisely this scenario to vendors who would give favoured appendages to deliver stronger protections to their users on iOS, the justification for Apple's security ceiling has a (very weak) point: browsers are a serious business, and doing a poor job has bad consequences. One must wonder, of course, how Apple treats applications with persistent security issues that aren't browsers. Are they un-published from the App Store? And if so, isn't that a reasonable precedent here?

Whatever the precedent, Apple is absolutely correct that browsers shouldn't be distributed without commitments to maintenance, and that vendors who fail to keep the pace with security patches shouldn't be allowed to degrade the security posture of end-users. Fortunately, these are terms that nearly every reputable browser developer can easily agree to.

Indeed, reputable browser vendors would very likely be willing to sign up to terms that only allow use of the (currently proprietary and private) APIs that Apple uses to create sandboxed renderer processes for WebKit if their patch and CVE-fix rates matched some reasonable baseline. Apple's recently-added Browser Entitlement provides a perfect way to further contain the risk: only browsers that can be set as the system default could be allowed to bring alternative engines. Such a solution preserves Apple's floor on abandonware and embedded WebViews without capping the potential for improved experiences.

There are many options for managing the clearly-identifiable case of abandonware browsers, assuming Apple managers are genuinely interested solutions rather than sandbagging the pace of browser progress. Setting high standards has broad support.

Just-In-Time Pretexts #

An argument that Apple hasn't made, but that others have derived from Apple's App Store Review Guidelines and instances of rejected app submissions, including Just-In-Time Compilers (JITs), has been that alternative browser engines are forbidden on iOS because they include JITs.

The history of this unstated policy is long, winding, and less enlightening than a description of the status quo:

• All major browser engines support both a JIT "fast path" for running JavaScript, as well as an "interpreted mode" that trades a JITs large gains in execution speed for faster start-up and lower memory use.
• JIT compilers are frequent sources of bugs, and a key reason why all responsible browser vendors put code downloaded from the web in sandboxes.
• Other iOS applications can embed non-JITing interpreters for JavaScript, if they like.
• Safari on iOS has been endowed with JIT for many years, whereas competing browsers were prevented from approaching similar levels of performance. More recently, WebView browsers on iOS have been able to take advantage of WebKit's JIT-ing JavaScript engine, but are prevented from bringing their own.

In addition to WebKit's lack of important JavaScript engine features (e.g. WASM Threads) and protections (Site Isolation), Apple's policy makes little sense on its visible merits.

Obviously, the speed delivered by JITs is important in browser competition, but it's also a fallacy to assume competitors wouldn't prefer the freedom to improve the performance, compatibility, and capabilities of the rest of their engines because they might not be able to JIT JavaScript. Every modern browser can run without a JIT, and many would prefer that to being confined to Apple's trailing-edge, low-quality engine.

So what does the prohibition on JITs actually accomplish?

As far as I can tell, disallowing other engines and their JIT-ing JavaScript runtimes mints Apple (but not users) two key benefits:

• Allowing other engines would mean providing access to the currently-private APIs that allow the creation of sandboxed subprocesses.^[4]
• Re-using the WebKit binary maximizes the sharing of "code pages" across processes. Practically speaking, this allows more programs to run simultaneously without the need for Apple to add more RAM to their devices. This, in turn, pads Apple's (considerable) margins in the construction of phones.

Blessing Safari as the only app allowed to mint sandboxed subprocesses, while preventing other from doing so, is clearly unfair. This one-sided situation has persisted because the details of sandboxing and process creation have been obscured by a blanket prohibition on alternative engines. Should Apple choose (or be required) to allow higher-quality engines, this private API should surely be made public, even if it's restricted to browsers.

Similarly, skimping on RAM in thousand-dollar phones seems a weak reason to deny users access to faster, safer browsers. The Chromium project has a history of strengthening the default sandboxes provided by OSes (including Apple's), and would no doubt love the try its hand at improving Apple's security floor qua ceiling.

The relative problems with JITs — very much including Apple's — are, if anything, an argument for opening the field to vendors who will to put in the work Apple has not to protect users. If the net result is that Cupertino sells safer devices while accepting a slightly lower margin (or an even more eye-watering price) on its super-premium devices, what's the harm? And isn't that something the market should sort out?

High-modernism may mean never having to admit you're wrong, but it doesn't keep one from errors that functional markets would discipline. You only learn about them, however, at the greatest of delays.

Diversity Perversity #

A final argument made by others, (but not by Apple who surely knows better), is that:

• Diversity in browser engines is desirable because, without competition, there is little reason for engines to keep improving.
• Apple's restrictions on iOS ensure that a heavily-used engine has a different codebase to the growing use of Blink/Chromium in other browsers.
• Therefore, Apple's policies are — despite their clear restrictions on engine choice — promoting the cause of engine diversity.

This is a slap-dash line of reasoning along several axes.

First, it fails to account for the different sorts of diversity that are possible within the browser ecosystem. Over the years, developers have suffered mightily under the thumb of entirely unwanted browser diversity in the form of trailing-edge browsers; most notably Internet Explorer 6).

The point of diversity and competition is to propel the leading edge forward by allowing multiple teams to explore alternative approaches to common problems. Competition at the frontier enables the market and competitive spirits to push innovation forward. What isn't beneficial is unused diversity potential. That is, browsers occupying market share but failing to push the state of the art forward in any meaningful way.

The solution to this sort of deadweight diversity has been market pressure. Should a browser fall far enough behind, and for long enough, developers will begin to suggest (and eventually require) users to adopt more modern options to access their services at the highest fidelity.

This is a beneficial market mechanism (despite its unseemly aspects) because it creates pressure on browsers to keep pace with user and developer needs. The threat of developers encouraging users to "vote with their feet" also helps ensure that no party can set a hard cap on the web's capabilities over time. This is essential to ensure that oligopolists cannot weaponise a feature gap to tax all software. The effect is to re-privatise standards-based low-level features and APIs by making them available only through proprietary frameworks and distribution channels while denying them to the web.

Apple's playbook has been to preserve the commons as a historical curiosity. Having blockaded every road to upgrading the web, Apple have made it impossible for an open platform to keep pace with Apple's own modern-but-proprietary options. The game's simple once pointed out, but hard to see at first because it depends on consistent inaction. This sort deadweight loss is hard to spot on short time horizons. Disallowing competitive engines that might upgrade the carrying capacity of freely-available alternatives may have been accidental at introduction of iOS, but it's value to Apple now can scarcely be overstated. After all, it's hard to extract ruinous taxes on a restive population with straightforward emigration options. No wonder Cupertino continues to perform new showings of the "web apps are a credible alternative on iOS!" pantomime.

In this understanding, the web helps maintain a fair market for software services. Web standards and open source web engines combine to create an interoperable commons across closed operating systems upon which services can be built without taxation; but only to the extent it's capable enough to meet user needs over time. Continuing to bring previouly proprietary features into the commons is the core mechanism by which this progress is delivered. Push notifications may have been new and shiny in 2011 but, a decade later, there's no reason to think that a developer should pay an ongoing tax for a feature that is offered by every major OS and device. The same goes for access to a phone's menagerie of sensors, as well as more efficient codecs.

The sorts of diversity we have come to value in the web ecosystem all live at the leading edge. Intense disputes about the best ways to standardize a use-case or feature are a strong sign of a healthy dynamic. It's rancid, however, when a single vendor can prevent progress across a wide swathe of domains that are critical to delivering better user experiences, and suffer no market consequence.

Apple has cut the fuel lines of progress by requiring use of WebKit in every iOS browser; choice without competition, distinction without difference. Users can have any sort of web they like, so long as it's as trailing-edge as Apple likes.

The sorts of diversity we have come to value in the web ecosystem all live at the leading edge. Intense disputes about the best ways to standardise some use-case or feature are a strong sign of a healthy dynamic. It's rancid, however, when a single vendor can prevent progress across a wide swathe of domains that are critical to delivering better user experiences and suffer no market consequence.

Yet this sort of participation-prize diversity is exactly what some (purported) defenders of Apple's policies would have us believe is, instead, healthy for the web.

It's a curious sort of argument. It seems to admit that Apple's engine is deeply sub-par (which it is) by way of excusing future failure to compete. It's not as though Apple is wanting for the funds and talent to build a competitive engine, however. It simply chooses not to. Apple's 2 trillion dollar market cap is paired with nearly $200 billion in cash on hand. One could produce a competitive browser for the spare change in Cupertino's Eames lounges.

Claims that foot-dragging must be protected because otherwise capable engines might win share is inadvertently back-handed. Excusing poor performance is to suggest that Apple does not possess the talent, skill, and resources to ever construct a competitive web engine. I, at least, think better of Apple's engineering acumen than do many of these nominal defenders.

More confusingly, it's unclear whether or not there should be any eclipse of WebKit in the offing, even if Apple were to allow other engines onto iOS while continuing to take up the rear on features, performance, and standards conformance. We have a natural experiment to this effect in Safari for MacOS. It continues to enjoy a high share of the Mac browser market despite stiff and legitimate browser competition on MacOS. Are Apple's defenders so certain that this won't be the natural result should iOS eventually provide a fair marketplace for browsers?

What is the worst-case scenario, exactly? That Safari loses share and Apple must respond by funding the WebKit team adequately? That the Safari team feels compelled to switch to another open source rendering engine (e.g. Gecko or Blink), preserving their ability to fork down the road, just as they did with KHTML, and as the Blink project did with WebKit?

None of these are close ended scenarios, nor must they result in a reduction in constructive, leading edge diversity. Edge, Brave, Opera, and Samsung Internet consistently innovate on privacy and other features without creating undue drag on core developer interests. Should the Chromium project become an unwelcome host for this sort of work, all of these organisations can credibly consider a fork, adding another new branch to the lineage of browser engines.

All of this has been in Apple's control. It's not a foregone conclusion the world's most valuable tech firm should produce the lowest-quality browser engine. The narratives in this space would surely be different if Apple's coercion about engine choice weren't paired with failure to keep pace across a wide variety of platform areas and features. A festering combination of low-quality and arm-twisting has created the current morass.

The point of diversity at the leading edge is progress through competition. The point of diversity amid laggards is the freedom to replace them — that's the market at work.

End Notes #

Nobody wishes it had come to this.

Apple's polices against browser choice were, at some point, relatively well grounded in the low resource limits of early smartphones. But those days are long gone. Sadly, the legacy of a closed choice, back when WebKit was still a leader in many areas, is an industry-wide hangover. We accepted a bad deal because the situation seemed convivial, and ignored those who warned it was a portent of a more closed, more extractive future for software.

Only if we had listened.

Joining a new team has surfaced just how much I've relied on a few lenses to explain the incredible opportunities and challenges of platform work. This post is the second in an emergent series towards a broader model for organisational and manager maturity in platform work, the first being last year's Platform Adjacency Theory. That article sets out a temporal model that focuses on trust in platforms. That trust has a few dimensions:

• Trust in reach. Does the platform deliver access to the users an app or service caters to? Will reach continue to expand at the rate computing does?
• Trust in capabilities. Can the platform enable the core use-cases of most apps in a category?
• Trust in governance. Often phrased as fear of lock-in, the goal of governance is to marry stability in the tax rate of a platform with API stability and reach.^[1]

These traits are primarily developer-facing for a simple reason: while the products that bring platforms to market have features and benefits, the real draw comes from safely facilitating trade on a scale the platform vendor can't possibly bootstrap on their own.

Search engines, for example, can't afford to fund producing even a tiny sliver of the content they index. As platforms, they have to facilitate interactions between consumers and producers outside their walls — and continue to do so on reasonably non-extractive terms.

Thinking about OSes and browsers gives us the same essential flavour: to make a larger market for the underlying product (some OS, browsers in general), the platform facilitates a vast range of apps and services by maximising developer reach from a single codebase at a low incremental cost. Those services and apps convince users to obtain the underlying products. This is the core loop at the heart of software platforms:

Cycles around the loop take time, and the momentum added or lost in one turn of the loop creates or destroys opportunity for the whole ecosystem at each successive step. Ecosystems are complex systems and grow and shrink through multi-party interplay.

Making progress through intertemporal effects is maddening to product-focused managers who are used to direct build ⇒ launch ⇒ iterate cycles. They treat ecosystems as static and immutable because, on the timescales they operate, that is apparently true. The lens of Pace Layering reveals the disconnect:

Products that include platforms iterate their product features on the commerce or fashion timescale, while platform work is the slower, higher-leverage movement of infrastructure and governance. Features added in a release for end-users have impact in the short run, while features added for developers may add cumulative momentum to the flywheel many releases later as developers pick up the new features and build new types of apps that, in turn, attract new users.

This creates a predictable bias in managers towards product-only work. Iterating on features around an ecosystem becomes favoured, even when changing the game (rather than learning to play it incrementally better) would best serve their interests. In extreme versions, product-only work leads to strip-mining ecosystems for short-term product advantage, undermining long-term prospects. Late-stage capitalism loves this sort of play.

The second common bias is viewing ecosystems that can't be fully mediated as somebody else's problem or as immovable. Collective action problems in open ecosystem management are abundant. Managers without much experience or comfort in complex spaces tend to lean on learned helplessness about platform evolution. "Standards are slow" and "we need to meet developers where they are" are the reasonable-sounding refrains of folks who misunderstand their jobs as platform maintainers to be about opportunities one can unlock in a single annual OKR cycle. The upside for organisations willing to be patient and intentional is that nearly all your competitors will mess this up.

Failure to manage platform work at the appropriate time-scale is so ingrained that savvy platform managers can telegraph their strategies, safe in the knowledge they'll look like mad people.

One might as well be playing cricket in an American park; the actions will look familiar to passers-by, but the long game will remain opaque. They won't be looking hard enough, long enough to discern how to play — let alone win.

At first glance, the market for mobile browsers looks roughly functional. The 85% global-share OS (Android) has historically facilitated browser choice and diversity in browser engines. Engine diversity is essential, as it is the mechanism that causes competition to deliver better performance, capability, privacy, security, and user controls. More on that when we get to iOS.

Tech pundits and policymakers form expectations of browsers on the desktop and think about mobile browser competition the same way. To recap:

• Users can freely choose desktop browsers with differing features, search engines, privacy features, security properties, and underlying engines.
• Browsers update quickly, either through integrated auto-update mechanisms or via fast OS updates (e.g., ChromeOS).
• Browsers bundled with desktop OSes represent the minority of browser usage, indicating a healthy market for replacements.
• Popular native apps usually open links in users' chosen browsers and don't undermine the default behaviour of link clicks.^[1]

Each point highlights a different aspect of ecosystem health. Together, these properties show how functioning markets work: clear and meaningful user choice creates competitive pressure that improves products over time. Users select higher quality products in the dimensions they care about most, driving quality and progress.

The mobile ecosystem appears to retain these properties, but the resemblance is only skin deep. Understanding how mobile OSes undermine browser choice requires a nuanced understanding of OS and browser technology. It's no wonder that few commenters are connecting the dots.^[2]

How bad is the situation? It may surprise you to learn that until late last year only Safari could be default browser on iOS. It may further disorient you to know that competing vendors are still prevented from delivering their own engines on iOS. Meanwhile, on Android, the #2 and #3 sources of web traffic do not respect browser choice. Users can have any browser with any engine they like, but it's unlikely to be used. The Play Store is little more than a Potemkin Village of browser choice; a vibrant facade to hide the rot.

Registering to handle link taps is only half the battle. For a browser to serve as the user's agent, it must also receive navigations. Google's Search App and Facebook's various apps for Android undermine these choices in slightly different ways.^[3] This reduces the effectiveness of privacy and security choices users entrust in their browsers. Developers also suffer higher costs and reduced opportunities to escape Google, Facebook, and Apple's walled gardens.

Web engineers frequently refer to browsers as "User Agents", a nod to their unique role as interpreters of developer intent that give users the final say over how the web is experienced. A silent erosion in the effectiveness of browser choice has transferred this power away from users, re-depositing it with dominant platforms and app publishers. To understand how this sell-out happened (quite literally) under our noses, we must look closely at how mobile and desktop differ.

The Baseline Scenario #

The predominant desktop situation is relatively straightforward:

Browsers handle links, and non-browsers defer loading http and https URLs to the system, which in turn invokes the default browser. This flow is the central transaction that gives links power and utility. If any of the players involved (OSes, browsers, or referring apps) violate aspects of the contract, user choice in browsers becomes less effective.

"What, then, is a 'browser'?" you might ask? I've got a long blog post brewing on this, but jumping to the end, an operable definition is:

A browser is an application that can register with an OS to handle http and https navigations by default.

On Android this is expressed via specific intent filters in the manifest and listing in the BROWSABLE category. iOS gained browser support in late 2020 (a dozen years late) via an Entitlement.^[4] Windows and other Desktop OSes have similar (if less tidy) mechanisms.

No matter how an OS technically facilitates user choice, it's this ability to choose that defines browsers as a class. How often links lead users to their preferred browser controls the meaningfulness of this choice.

Android's "In-App Browser" Problem(s) #

The history of mobile computing starts from an incredibly resource-constrained point. First-generation iOS and Android smartphones were slow single-core, memory-impoverished affairs, leading mobile OSes to learn new tricks to facilitate responsive computing. Android and iOS adopted heuristics to kill and reclaim RAM used by non-foreground apps when resource pressure intensified.

This background task killing behaviour created unique problems for link-heavy apps. Launching the user's browser placed linking apps in the background, increasing friction in returning to the sending app, as browser UI did not provide affordances for returning to referring applications. Being put in the background also increases the likelihood of being killed.^[5] Returning to the source app while in this state can feel excruciating. It can take seconds to re-start the original app and restore the UI state, an experience that gets worse on low-end devices that are most likely to evict apps in the first place.

Engagement-thirsty apps began including "In-App Browsers" ("IABs") to address these challenges. Contrary to any plain-language understanding of "a browser", these IABs cannot generally be installed as the default handler for links, even when OSes support browser choice. Instead, they load content referred by their hosting native app in system-provided WebViews.

The benefits to apps that adopt WebView-based IABs are numerous:

• WebViews are system components designed for use within other apps. They do not place embedders in the background where the system may kill them to reclaim resources. This reduces friction and commensurately increases "engagement" metrics.^[6]
• As they are now "the browser", they can provide UI that makes returning to the host application easier than continuing on the web.
• Because they lean on the system-provided WebView component, they do not need to pay the expense of a heavier app download to support rendering HTML, running JavaScript, decoding images, or loading network resources.
• Apps can customise UI to add deeper integrations, e.g., "pinning" images from a hosted page to Pinterest.
• On Android today and early iOS versions, WebViews allow embedders to observe and modify all network traffic (regardless of encryption). Apps can also monitor user input, resulting DOM, and system auto-filled credentials.

To the extent that users are comfortable with apps not remembering their previously-stored passwords, login state, privacy preferences, extensions, or accessibility configurations, this can be a win-win.

Conversely, the web feels broken when any one of those conditions is not met.

Thanks to the light (bordering on non-existent) attribution back to the hosting app, along with disjoint and buried user controls to disable this misfeature, users may think the web isn't worth visiting, or that their browser broke.^[7]

1...2...3...Party Time! #

WebViews are the source of much confusion in debates around apps and browser choice. Thankfully, the situation is only complicated rather than complex.

There are two dimensions in play:

• Can the app register with an OS to handle http/https navigations by default?
  • If so, it's a browser regardless of the underlying engine.
  • If not, it's something else; a "content renderer" or an IAB.
• Does the app include its own web engine?
  • If so, it's integrated — e.g., an "Integrated Browser".
  • If not, it's WebView-powered, e.g. a "WebView Browser" or "WebView IAB".

So, a browser can be WebView-based, and so can an IAB. But neither has to be.

What is a WebView? To quote the Android documentation, a WebView is...:

A View that displays web pages. ... In most cases, we recommend using a standard web browser, like Chrome, to deliver content to the user.

WebViews have a long history in mobile OSes, filling several roles:

• Rendering HTML on behalf of the first-party application developer.
• Displaying cooperating, second-party content like ads.
• Providing the core of browsers, whose job is to display third-party content. The original Android Browser used early-Android's system WebView, for instance.

The power dynamics of these situations are starkly different, even though "web technology" is used to render content in each case.

The use of a "raw" WebView is entirely appropriate for first and second-party content. Here, native apps are doing work related to their core function; storage and tracking of user data are squarely within the four corners of the app's natural responsibilities. Furthermore, the content developer is unlikely to find limits presented by the WebView to be unwelcome or unreasonably immutable (via collaboration with the app developer). Instead of breaking content, WebViews are likely to facilitate it in these scenarios faithfully.

All bets are off regarding WebViews and third-party content, however. To understand why it helps to know that WebViews are not browsers.

WebViews contain core browser features, along with hooks that allow embedders to "light up" many more. However, producing a complete and competitive WebView-based browser requires additional UI and glue code. In particular, features that require permission-gated access to privileged services need explicit support from embedders to work as specified.

Features in this category include:

• Privacy and site quality support, including "acceptable ads" enforcement and browser history clearing.
• Security indicators (TLS padlock, interstitial warnings, etc.)
• Basic navigation and window management features to (e.g. window.open() and <a target="_blank"> which are critical to some site monetization features).
• Friction reducing OS integrations such as:
  • Web Payments (streamlined e-commerce checkout)
  • Web OTP (for easier/faster sign-in)
  • Web Share
• Hardware access APIs, notably:
  • Geolocation
  • Camera/mic (getUserMedia())
  • Web Bluetooth
  • WebUSB
  • Web Serial
  • WebHID
  • WebMIDI
  • Web NFC
  • Filesystem Access
• Re-engagement features including:
  • PWA installation and home screen shortcuts for sites
  • Push Notifications

Few (if any) WebView browsers implement all of these features, even when their underlying WebViews support bindings for them.

The situation is even more acute in WebView IABs, which tend not to fully support features from these categories even when they appear available to developers via script. Worse, debugging from these IABs is challenging, compounded by a lack of awareness about how much traffic may come from these sources.

How can that be? Web developers are accustomed to real browsers in the desktop mould. Standard tools, analytics packages, and feature availability dashboards do not make mention of IABs, and the largest WebView IAB promulgators (Facebook, Pinterest, Snap, etc.) have invested almost nothing in clarifying the situation.

It's vital to understand that neither users nor developers chose Facebook, Pinterest, or Google Go as a browser. The flow that WebView IABs present denies users agency over their choices, and technical limits imposed by them often prevent developers from opening content in real browsers.

No documentation is available for third-party web developers from any of the largest WebView IAB (ab)users. This absence mirrors the scandalous free-riding of these app publishers regarding browser feature support, which is perhaps not surprising. It is, however, all the more egregious for the subtlety and scale of breakage.

If Facebook, the third largest "browser"-maker for Android, employs a single developer relations engineer or doc writer to cover these issues, I'm unaware of it. Meanwhile, forums are full of melancholy posts recounting myriad ways these submarine renderers break features that work in other browsers.

Having been given "the first 80%" of a browser, with development and distribution of critical components subsidised by OS vendors, WebView IABs near-universally fail to keep up their end of the bargain with either users or developers. First-party webdevs can collaborate with their app-development colleagues to build custom access for any exotic feature supported by the OS. Second-party developers expect less (ads are generally not given broad feature access). But third-party developers? They are as helpless as users are to understand why an otherwise browser-presenting environment appears subtly, yet profoundly, broken.

Maximiliano Firtman @firt

There are still users browsing with a Chrome 37 engine (7 years ago), not because they don't update their browsers but because it's Facebook Mobile Browser on Android 5 using a webview. Facebook does NOT honor user browser choice leaving that user with an old engine. +

52 12:12 PM · Jul 15, 2021

These same app publishers request (and heavily use) features within real browsers they do not enable for others, even when spotted the bulk of the work. Perhaps browser and platform vendors should consider denying these apps access to capabilities they undermine for others.

WebView IAB User Harms #

The consequences of WebView IABs on developers are noteworthy, but it's the impacts on users that inspire confusion and rage.

Consider again the desktop reference scenario:

Clicking links from apps transfers control to an external browser which dutifully applies the user's stored preferences and accumulated state. Login credentials for example.com are not forgotten when a link is followed from an email. The same unified experience ensures that saved addresses and payment information are readily available. Most importantly, accessibility settings and privacy preferences are consistently applied.

By contrast, WebView IABs fracture user state, storing it in silos within each hosting application, creating a continuous partial amnesia.

The confusion that reliably results is the consequence of an inversion of the power relationship between apps and websites.

Does any user expect that everything one does on any website loaded from a link in the Facebook app, Instagram, or Google Go can be fully monitored by those apps? That all passwords shared and the full scope of sites visited from the first page can potentially be recorded and tracked?^[8] To be clear, there's no record of these apps using this extraordinary access in overtly hostile ways, but even the unintended side-effects reduce user control over data and security.

Retaining onward links is not objectionable in programs that also offer themselves as browsers, but the WebView IAB sleight of hand is to act as a browser when users least expect it, but never to cop to the power and privacy implications of the responsibilities browsers accept.

CCT: A New Hope? #

Libraries emerged to facilitate the construction of WebView IABs, leading to a recognition by OS and browser vendors that users were becoming confused and developers irate.

To address this challenge, Apple introduced SFSafariViewController and Google followed suit with the inartfully-named Chrome Custom Tabs protocol and helper library. Both systems allow native app developers to skip the drudge work of building a WebView IAB system and instead work with the OS to invoke the user's default browser to load web pages within the context of the host app. Similarly to WebView IABs, CCT and SFSVC address background eviction and lost app state. However, because they invoke the user's actual browser, they also prevent user confusion whilst delivering the complete set of features supported by proper browsers.

These solutions come at the cost of some flexibility for app developers who lose access to read network traffic between users and third-party sites. They also cannot inspect and change page content trivially, removing the ability to add new, non-standard features to their IABs. Counterbalancing these concerns, CCT and SFSVC restore user choice^[9] and ensure developers access to the complete set of browser features.

Et Tu, Google? #

CCT sounds pretty great, huh?

Well, it is. At least in the default configuration. Despite the clunky inclusion of "Chrome" in the name, the CCT library and protocol are browser-agnostic. A well-behaved CCT-invoking-app (e.g., Twitter for Android) will open URLs in the CCT-provided IAB-alike UI via Firefox, Brave, Samsung Internet, Edge, or Chrome if they are the system default browser.

That is unless the native app overrides the default behaviour and invokes a specific browser.

Ada Rose Cannon @AdaRoseCannon

@slightlylate I recently was talking to my Dad about the Web and asked what browser he uses and he showed me what he does:
He searches for the Web site in the Google search widget and then just uses the results page Chrome tab as his entire browser.
His default browser is not set to Chrome.

5 06:21 PM · Jul 15, 2021

Who would do this, you might ask? None other than Google's own Search App; you know the one that comes on every reputable Android device via the ubiquitous home screen search widget.

Known as the "Android Google Search App" ("AGSA", or "AGA"), this humble text input is the source of a truly shocking amount of web traffic; traffic that all goes to Chrome, no matter the user's choice of browser.

There were justifiable reasons to add code like this. Early in the life of the CCT protocol, before support was widespread, many browsers exhibited showstopper bugs. 2021 is far advanced from those early days, however, and so the primary effect of calling to Chrome is to distort the market for browsers and undermine user choice. This behaviour subverts user privacy, undermines the ecosystem benefits of engine diversity, and makes it hard for alternative browsers to compete on a level playing field.

This situation is admittedly better than the wholesale neutering of important developer-facing features by WebView IABs, but a Hobson's Choice none the less.

WebLayer: New Frontiers In User Confusion #

Google can (and should) revert to the system default of affirmatively respecting user choice in browsers by deleting the offending choice override. Given that AGSA uses CCT to load web pages rather than a WebView, this is nearly trivial today. CCT's core design is sound and has enormous potential if made mandatory in place of WebView IABs by the Android and Play teams.

There's reason to worry that this is unlikely.

Instead of addressing frequent developer requests for features in the CCT library, the Chrome for Android team has invested heavily in the "WebLayer" project. You can think of WebLayer like a WebView-with-batteries-included, repairing issues related to missing features but continuing to fracture state and user choice.

There is a positive case for WebLayer: as a replacement for WebViews in the context of browsers, it's a major step forward. In the context of IABs, however, WebLayer looks set to entrench user-hostile patterns further.

This subversion of choice extends a dispiriting trend in search apps that fancy themselves browsers without even attempting to earn a user's business as a browser.

In addition to Google Go, the Google app for iOS as well as Microsoft's Bing app for Android both capture outbound links in WebView IABs, subverting both browser choice and feature availability for developers. If there's any mercy, it's that their relatively lower use somewhat limits their impact on the overall ecosystem. Adopting WebLayer will not meaningfully improve the user experience or privacy of these amnesiac browsing experiences.

Google and Apple have the chance to lead, to show they aren't hostile to users, and remove the permission structure for lousy behaviour that less scrupulous players exploit. More on that in a moment.

iOS's Outsized, Malign Influence #

Imagine if automakers could only use one government-mandated engine model across all cars and trucks. Different tires and upholstery only go so far. If the engine is underpowered, many tasks might not be possible, rendering whole vehicle classes pointless. That's the situation iOS creates for browser makers and the browser-downloading public, and the only recourse it to buy a new phone.

iOS matters because wealthy users carry iPhones. It's really as simple as that. Even when Apple's products fail to gain a numerical majority of users in a market, the margin contribution of iOS users can dominate all other business considerations.

From at least 2012, Apple has deigned to allow "competing browsers" in its App Store. Those applications could not be browsers in any meaningful sense as they could not supplant Safari as the default handler of http/https links. The long charade of choice without effect finally ended with the release of iOS 14.2 in late 2020, bringing iOS into line with every other significant OS in supporting alternative browsers.^[10]

But Apple has taken explicit and extensive care to ensure that this choice is only ever skin deep on iOS. Browsers on Windows, Linux, ChromeOS, Android, and MacOS can be Integrated Browsers. iOS, meanwhile, restricts browsers to shells over the system-provided WebView.

Unlike WebView browsers on other OSes, Apple locks down these components in ways that prevent competition in additional areas, including restrictions on network stacks that block improved performance, new protocols, or increased privacy. These restrictions make some sense in the context of WebView IABs, but extending them to browsers only serves to deflect pressure from Apple to improve their browser.

Perhaps it would be reasonable for iOS to foreclose competition from integrated browsers and insist on uniquely constrained WebViews. Such policies would represent a different view of what computing should be if native apps were required to live within similar limits. However, Apple is happy to provide a much wider variety of features to unsafe native applications so long as they comply with the coercive terms of its App Store.

Integrated browsers present a model that, if allowed to flourish, pose a threat to the fundamentals of Apple and Google's whale-based, dopamine fueled, "casual" gaming monetisation rackets.

Unlike other native apps, integrated browsers are principally concerned with user safety. A safe-by-default, capable platform with low-friction discovery could obviate the core justification for app stores: that they're necessary to keep in check the over-powered-by-default apps built to an OS's proprietary platform.

Apple forestalls this bottom-line threat by keeping the web on iOS from gaining reasonable feature parity. Outlawing integrated browser choice leaves only Apple's own, farcially under-powered, Safari/WebKit browser/engine...and there's precious little that other WebView browsers can do to improve the situation at a deep level.^[11]

Web developers are understandably livid:

Ada Rose Cannon @AdaRoseCannon

Seeing a Web App I worked on used by *Apple* to justify that the Web is a viable platform on iOS is bullshit

The Web can be an ideal place to build apps but Apple is consistently dragging their heals on implementing the Web APIs that would allow them to compete with native apps twitter.com/stopsatgreen/status/1389593307219701760

692 06:05 PM · May 4, 2021

Ada Rose Cannon @AdaRoseCannon

In addition, by refusing to let any other Web browser engines run on iOS. They are preventing any other browser filling in the feature gap. Truly holding back Web Apps on iOS.

149 06:05 PM · May 4, 2021

Ada Rose Cannon @AdaRoseCannon

I have defended Apple's choice to restrict web browsers on their platform before and I still do but they can't have their cake and eat it to.

They should not hold back Web Apps with one hand and then turn around and say that Web Apps can compete with native apps.

153 06:10 PM · May 4, 2021

Pointing to a site of serial developer mistreatment to justify other developer-hostile App Store policies takes next-level chutzpah.

Developer anger only hints at the underlying structural rot. 25+ years of integrated browser competition has driven waves of security, capability, and performance improvements. Competition has been so effective in delivering these benefits that browsers now represent most computing time on OSes with meaningful and integrated browser choice.

Hollowing out browser choice while simultaneously starving Safari and WebKit of resources, somewhat miraculously, put the genie back in the bottle. Privacy, security, performance, and feature evolution all suffer when the competition is less vibrant — and that's how Apple likes it.

Mark(et)d Impacts #

A vexing issue for commentators regarding Apple's behaviour in this area is that of "market definition". What observers should understand is that, in the market for browsers, the costs that a browser vendor can inflict on web developers extend far beyond the market penetration for their specific product.

A typical (but misleading) shorthand for this is "standards compliance". While Apple's engine falls woefully short on support for ratified standards, that isn't even the beginning of the negative impacts.^[12] Because the web is an open, interoperable platform, web developers build sites to reach the vast majority of browsers from a single codebase.

When browsers with more than ~10% share fail to add a feature or exhibit nasty bugs, web developers must pay attention and work around these limitations. In the case of outright missing APIs, entire classes of content may simply be viewed as unworkable. The cost of these capability gaps is steep. When the web cannot deliver experiences that iOS native apps can (a very long list), businesses must build entirely different apps using Apple's proprietary tools. These apps, not coincidentally, can only be distributed via Apple's high-tax App Store.

A lack of meaningful user choice in browsers leads directly to higher costs for users and developers across the entire digital ecosystem even if they don't use Apple's products. The permission structure Apple's norm-eroding policies have constructed has served to justify some of the worst privacy and choice-undermining behaviour of tech giants. Apple's leadership in the race to the bottom has inspired a burgeoning field of fast-followers.

Beyond direct harms, interested parties should not consider browser choice as somehow orthogonal to other objectionable App Store policies; they are part and parcel of an architecture of control that tilts commerce into coercive, centralising App Stores. No matter how Apple wants to define the market, its actions distort and undermine competition.

Small Changes to Restore Choice #

Here's a quick summary of the systems and variations we've seen thus far, as well as their impacts on user choice:

Proposals to repair this profoundly broken situation must centre first on the effectiveness of browser choice. Some policymakers have suggested returning to browser choice ballots, however these will not be effective in a world where user choice is undermined no matter which browser they choose. Interventions to encourage informed browser choice cannot have a positive effect until the impact of choices can be assured.

Thankfully, repairing the integrity of browser choice in the mobile ecosystem can be accomplished with relatively small interventions. We only need to ensure that integrated browsers are universally available and that when third-party content is displayed, user choice of browser is respected.

Android #

Repairing the IAB situation will likely require multiple steps, given the extreme delay in new Android OS revisions gaining a foothold in the market. Thankfully, many fixes don't need OS updates:

• Google should update the CCT system to respect browser choice when loading third-party content and require updates to CCT-using apps to this new behaviour within six months.

  • Verification of first-party content for use with specific engines is possible thanks to the Digital Asset Links infrastructure that underpins Trusted Web Activities, the official mechanism for putting web apps in the Play Store.

• AGSA and Google Go should respect user choice via CCT.

• Android's WebView and WebLayer should be updated with code to detect a new HTTP header value sent with top-level documents that cause the URL to be opened in the user's default browser (or a CCT for that browser) instead.

  • These systems update out-of-band every six weeks on 90+% of devices, delivering quick relief.
  • As a straw-person design, the existing Content Security Policy system's frame-ancestors mechanism can be extended with a new 'system-default' value.
  • Such an opt-out mechanism preserves WebViews for first-party and second-party use-cases (those sites will simply not set the new header) while giving third-parties a fighting chance at being rendered in the user's default browser.
  • Apps that are themselves browsers (can be registered as default http/https handlers) would be exempt, preserving the ability to build WebView browsers. "Browserness" can be cheaply verified via an app's manifest.

• Google should provide access to all private APIs currently reserved to Chrome, including but not limited to the ability to install web applications to the system (a.k.a. "WebAPKs").

Future releases of Android should bolster these improvements by creating system-wide opt-out of WebView and WebLayer IABs.

Play policy enforcement of rules regarding CCT, WebView, and WebLayer respect for user and developer choice will also be necessary. Such enforcement is not challenging for Google, given its existing binary analysis infrastructure.

Together, these small changes can redress the worst anti-web, anti-user, anti-developer, and anti-choice behaviour of Google and Facebook regarding Android browsers, putting users back in control of their data and privacy along the way.

iOS #

iOS begins from a more troubling baseline but with somewhat better IAB policies. What's undermining user choice there require deeper, OS-level fixes, including:

• Integrated browser choice, including access to APIs that iOS restricts to Safari today, such as:

  • The ability to create sandboxed subprocesses for renderers.
  • Push Notifications APIs.
  • Adding web apps to the home screen, including PWA installation.
  • Support in Web.app for alternative engine runtimes to ensure that home screen shortcuts and PWAs run in the correct context.

• SFSafariViewController support for browsers other than Safari.

• All apps that load non-consenting third-party websites (outside of edge cases like authentication flows) in IABs should be required to update to SFSafariViewController,

• Apple's WebViews should support Content-Security-Policy: frame-ancestors 'system-default'

Allowing integrated browsers will require updates to Apple's App Store policies to clarify that alternative engines are permitted in the context of com.apple.developer.web-browser entitled applications.

For Markets To Work, Choice Must Matter #

The mobile web is a pale shadow of its potential because the vehicle of progress that has delivered consistent gains for two decades has silently been eroded to benefit native app platforms and developers. These attacks on the commons have at their core a shared disrespect for the sanctity of user choice, substituting the agenda of app and OS developers for mediation by a user's champion.

This power inversion has been as corrosive as it has been silent, but it is not too late. OSes and app developers that wish to take responsibility can start today to repair their own rotten, choice-undermining behaviour and put users back in control of their browsing, their data, and their digital lives.

The ball's in your court, platforms.

Git Worktrees appear to solve a set of challenges I encounter when working on this blog:

1. Maintenance branches for 11ty and other dependencies come and go with some frequency.
2. Writing new posts on parallel branches isn't fluid when switching frequently.
3. If I incidentally mix some build upgrades into a content PR, it can be difficult to extract and re-apply if developed in a single checkout.

Worktrees hold the promise of parallel working branch directories without separate backing checkouts. Tutorials I've found seemed to elide some critical steps, or required deeper Git knowledge than I suspect is common (I certainly didn't have it!).

After squinting at man pages for more time than I'd care to admit and making many mistakes along the way, here is a short recipe for setting up worktrees for a blog repo that, in theory, already exists at github.com/example/workit:

##
# Make a directory to hold a branches, including main
##

$ cd /projects/
$ mkdir workit
$ cd workit
$ pwd
# /projects/workit

##
# Next, make a "bare" checkout into `.bare/`
##

$ git clone --bare git@github.com:example/workit.git .bare
# Cloning into bare repository '.bare'...
# remote: Enumerating objects: 19601, done.
# remote: Counting objects: 100% (1146/1146), done.
# ...

##
# Tell Git that's where the goodies are via a `.git`
# file that points to it
##

$ echo "gitdir: ./.bare" > .git

##
# Now we can use worktrees.
#
# Start by checking out main; will fetch repo history
# and may therefore be slow.
##

$ git worktree add main
# Preparing worktree (checking out 'main')
# ...
# Filtering content: 100% (1226/1226), 331.65 MiB | 1.17 MiB/s, done.
# HEAD is now at e74bc877 do stuff, also things

##
# From here on out, adding new branches will be fast
##

$ git worktree add test
# Preparing worktree (new branch 'test')
# Checking out files: 100% (2216/2216), done.
# HEAD is now at e74bc877 do stuff, also things

##
# Our directory structure should now look like
##

$ ls -la
# total 4
# drwxr-xr-x 1 slightlyoff eng   38 Jul  7 23:11 .
# drwxr-xr-x 1 slightlyoff eng  964 Jul  7 23:04 ..
# drwxr-xr-x 1 slightlyoff eng  144 Jul  7 23:05 .bare
# -rw-r--r-- 1 slightlyoff eng   16 Jul  7 23:05 .git
# drwxr-xr-x 1 slightlyoff eng  340 Jul  7 23:11 main
# drwxr-xr-x 1 slightlyoff eng  340 Jul  7 23:05 test

##
# We can work in `test` and `main` independently now
##

$ cd test
$ cat "yo" > test.txt
$ git add test.txt
$ git commit -m "1, 2, 3..." test.txt
# [test 2e3f30b9] 1, 2, 3...
#  1 file changed, 1 insertion(+)
#  create mode 100644 test.txt

$ git push --set-upstream origin test
# ...

Thankfully, commands like git worktree list and git worktree remove are relatively WYSIWYG by comparison to the initial setup.

Perhaps everyone else understands .git file syntax and how it works with --bare checkouts, but I didn't. Hopefully some end-to-end exposition can help drive adoption of this incredibly useful feature.

Update (June 16th, 2021): Folks attempting to build mobile web games have informed me that the Fullscreen API remains broken on iOS for non-video elements. This hobbles gaming and immersive media experiences in a way that is hard to overstate. Speaking of being hobbled, the original post gave Apple credit for eventually shipping a useable implementation of IndexedDB. It seems this was premature.

Three facts...

1. Apple bars web apps from the only App Store allowed on iOS.^[1]
2. Apple forces developers of competing browsers to use their engine for all browsers on iOS, restricting their ability to deliver a better version of the web platform.
3. Apple claims that browsers on iOS are platforms sufficient to support developers who object to the App Store's terms .

...and a proposition:

Apple's iOS browser (Safari) and engine (WebKit) are uniquely under-powered. Consistent delays in the delivery of important features ensure the web can never be a credible alternative to its proprietary tools and App Store.

This is a bold assertion, and proving it requires overwhelming evidence. This post mines publicly available data on the pace of compatibility fixes and feature additions to assess the claim.

Steve & Tim's Close-up Magic #

Misdirections often derail the debate around browsers, the role of the web, and App Store policies on iOS. Classics of the genre include:

Apple's just focused on performance!

...that feature is in Tech Preview

Apple's trying, they just added <long-awaited feature>

These points can be simultaneously valid and immaterial to the web's fitness as a competent alternative to native app development on iOS.

To understand the gap Apple created and maintains between the web and native, we should look at trends rather than individual releases. To know if we're in a drought, we have to check reservoir levels and seasonal rainfall. It might be raining features right this instant, but weather isn't climate.

Before we get to measuring water levels, I want to make some things excruciatingly clear.

First, what follows is not a critique of individuals on the Safari team or the WebKit project; it is a plea for Apple to fund their work adequately^[2]. They are, pound for pound, some of the best engine developers globally and genuinely want good things for the web. Apple Corporate is at fault, not Open Source engineers or the line managers who support them.

Second, browser projects having different priorities at the leading edge is natural and healthy. So is speedy resolution and agreement. What's unhealthy is an engine trailing far behind for many years. Even worse are situations that cannot be addressed through browser choice. It's good for teams to be leading in different areas, assuming that the "compatible core" of features continues to expand at a steady pace. We should not expect uniformity in the short run — it would leave no room for leadership^[3].

Lastly, while this post does measure the distance Safari lags, let nobody mistake that for the core concern: iOS App Store policies that prevent meaningful browser competition are at issue here.

Safari trails competing MacOS browsers by roughly the same amount, but it's not a crisis because genuine browser choice enables meaningful alternatives.

MacOS Safari is compelling enough to have maintained 40-50% share for many years amidst stiff competition. Safari has many good features, and in an open marketplace, choosing it is entirely reasonable.

The Performance Argument #

As an engineer on a browser team, I've been privy to the blow-by-blow of various performance projects, benchmark fire drills, and the ways performance marketing impacts engineering priorities.

All modern browsers are fast, Chromium and Safari/WebKit included. No browser is always fastest. As reliably as the Sun rises in the East, new benchmarks launch projects to re-architect internals to pull ahead. This is as it should be.

Healthy competitions feature competitors trading the lead with regularity. Spurious reports of "10x worse" performance merit intense scepticism.

After 20 years of neck-in-neck competition, often starting from common code lineages, there just isn't that much left to wring out of the system. Consistent improvement is the name of the game, and it can still have positive impacts, particularly as users lean on the system more heavily over time.

All browsers are deep into the optimisation journey, forcing complex tradeoffs. Improving things for one type of device or application can regress them for others. Significant gains today tend to come from (subtly) breaking contracts with developers in the hopes users won't notice. There isn't a massive gap in focus on performance engineering between engines.

Small gaps and a frequent hand-off of the lead imply differences in capability and correctness aren't the result of one team focusing on performance while others chase different goals^[4].

Finally, the choice to fund feature and correctness work is not mutually exclusive to improving performance. Many delayed features on the list below would allow web apps to run faster on iOS. Internal re-architectures to improve correctness often yield performance benefits too.

The Compatibility Tax #

Web developers are a hearty bunch; we don't give up at the first whiff of bugs or incompatibility between engines. Deep wells of knowledge and practice centre on the question: "how can we deliver a good experience to everyone despite differences in what their browsers support?"

Adaptation is a way of life for skilled front enders.

The cultural value of adaptation has enormous implications. First, web developers don't view a single browser as their development target. Education, tools, and training all support the premise that supporting more browsers is better (ceteris paribus), creating a substantial incentive to grease squeaky wheels. Therefore, bridging the gap between leading and trailing-edge browsers is an intense focus of the web development community. Huge amounts of time and effort are spent developing workarounds (preferably with low runtime cost) for lagging engines^[5]. Where workarounds fail, cutting features and UI fidelity is understood to be the right thing to do.

Compatibility across engines is key to developer productivity. To the extent that an engine has more than 10% share (or thereabouts), developers tend to view features it lacks as "not ready". It's therefore possible to deny web developers access to features globally by failing to deliver them at the margin.

A single important, lagging engine can make the whole web less competitive this way.

To judge the impact of iOS along this dimension, we can try to answer a few questions:

1. How far behind both competing engines is Safari regarding correctness?
2. When Safari has implemented essential features, how often is it far ahead? Behind?

Thanks to the Web Platform Tests project and wpt.fyi, we have the makings of an answer for the first:

The yellow Safari line is a rough measure of how often other browsers are compatible, but Safari's implementation is wrong. Conversely, the much lower Chrome and Firefox lines indicate Blink and Gecko are considerably more likely to agree and be correct regarding core web standards^[6].

wpt.fyi's new Compat 2021 dashboard narrows this full range of tests to a subset chosen to represent the most painful compatibility bugs:

In almost every area, Apple's low-quality implementation of features WebKit already supports requires workarounds. Developers would not need to find and fix these issues in Firefox (Gecko) or Chrome/Edge/Brave/Samsung Internet (Blink). This adds to the expense of developing for iOS.

Converging Views #

The Web Confluence Metrics project provides another window into this question.

This dataset is derived by walking the tree of web platform features exposed to JavaScript, an important subset of features. The available data goes back further, providing a fuller picture of the trend lines of engine completeness.

Engines add features at different rates, and the Confluence graphs illuminate both the absolute scale of differences and the pace at which releases add new features. The data is challenging to compare across those graphs, so I extracted it to produce a single chart:

In line with Web Platform Tests data, Chromium and Firefox implement more features and deliver them to market more steadily. From this data, we see that iOS is the least complete and competitive implementation of the web platform, and the gap is growing. At the time of the last Confluence run, the gap had stretched to nearly 1000 APIs, doubling since 2016.

Perhaps counting APIs gives a distorted view?

Some minor additions (e.g. CSS's new Typed Object Model) may feature large expansions in API surface. Likewise, some transformative APIs (e.g. webcam access via getUserMedia() or Media Sessions) may only add a few methods and properties.

To understand if intuitions formed by the Web Confluence data are directionally correct, we need to look more deeply at the history of feature development and connect APIs to the types of applications they enable.

Material Impacts #

Browser release notes and caniuse tables since Blink forked from WebKit in 2013^[7] capture the arrival of features in each engine over an even longer period than either WPT or the Confluence dataset. This record can inform a richer understanding of how individual features and sets of capabilities unlock new types of apps.

Browsers sometimes launch new features simultaneously (e.g., CSS Grid and ES6). More often, there is a lag between the first and the rest. To provide a sizeable "grace period", and account for short-run differences in engine priorities, we look primarily at features with a gap of three years or more^[8].

What follows is an attempt at a full accounting of features launched in this era. A summary of each API and the impact of its absence accompanies every item.

Where Chrome Has Lagged #

It's healthy for engines to have different priorities, leading every browser to avoid certain features. Chrome has missed several APIs for 3+ years:

Storage Access API

Introduced in Safari three years ago, this anti-tracking API was under-specified, leading to significant divergence in API behaviour across implementations. The low quality of Apple's initial versions of "Intelligent Tracking Prevention" created a worse tracking vector(pdf) (subsequently repaired)^[9].

On the positive side, this has spurred a broader conversation around privacy on the web, leading to many new, better-specified proposals and proposed models.

CSS Snap Points

Image carousels and other touch-based UIs are smoother and easier to build using this feature. Differences within the Blink team about the correct order to deliver this vs. Animation Worklets led to regrettable delays.

Initial Letter

An advanced typography feature, planned in Blink once the LayoutNG project finishes.

position: sticky

Makes "fixed" elements in scroll-based UIs easier to build. The initial implementation was removed from Blink post-fork and re-implemented on new infrastructure several years later.

CSS color()

Wide gamut colour is important in creative applications. Chrome does not yet support this for CSS, but is under development for <canvas> and WebGL.

JPEG 2000

Licensing concerns caused Chrome to ship WebP instead.

HEVC/H.265

Next-generation video codecs, supported in many modern chips, but also a licensing minefield. The open, royalty-free codec AV1 has been delivered instead.

Where iOS Has Lagged #

Some features in this list were launched in Safari but were not enabled for other browsers forced to use WebKit on iOS (e.g. Service Workers, getUserMedia). In these cases, only the delay to shipping in Safari is considered.

getUserMedia()

Provides access to webcams. Necessary for building competitive video experiences, including messaging and videoconferencing.

These categories of apps were delayed on the web for iOS by five years.

WebRTC

Real-time network protocols for enabling videoconferencing, desktop sharing, and game streaming applications.

Delayed five years.

Gamepad API

Fundamental for enabling the game streaming PWAs (Stadia, GeForce NOW, Luna, xCloud) now arriving on iOS.

Delayed five years.

Audio Worklets

Audio Worklets are a fundamental enabler for rich media and games on the web. Combined with WebGL2/WebGPU and WASM threading (see below), Audio Worklets unlock more of a device's available computing power, resulting in consistently good sound without fear of glitching.

After years of standards discussion and the first delivered to other platforms in 2018, iOS 14.5 finally shipped Audio Worklets this week.

IndexedDB

A veritable poster-child for the lateness and low quality of Safari amongst web developers, IndexedDB is a modern replacement for the legacy WebSQL API. It provides developers with a way to store complex data locally.

Initially delayed by two years, first versions of the feature were so badly broken on iOS that independent developers began to maintain lists of show-stopping bugs.

Had Apple shipped a usable version in either of the first two attempts, IndexedDB would not have made the three-year cut. The release of iOS 10 finally delivered a workable version, bringing the lag with Chrome and Firefox to four and five years, respectively.

Pointer Lock

Critical for gaming with a mouse. Still not available for iOS or iPadOS.

Media Recorder

Fundamentally enabling for video creation apps. Without it, video recordings must fit in memory, leading to crashes.

This was Chrome's most anticipated developer feature ever (measured by stars). It was delayed by iOS for five years.

Pointer Events

A uniform API for handling user input like mouse movements and screen taps that is important in adapting content to mobile, particularly regarding multi-touch gestures.

First proposed by Microsoft, delayed three years by Apple^[10].

Service Workers

Key API enabling modern, reliable offline web experiences and PWAs.

Delayed three years (Chrome 40, November 2014 vs. Safari 11.1, April 2018, but not usable until several releases later).

WebM and VP8/VP9

Royalty-free codecs and containers; free alternatives to H.264/H.265 with competitive compression and features. Lack of support forces developers to spend time and money transcoding and serving to multiple formats (in addition to multiple bitrates).

They are supported only for use in WebRTC but not the usual mechanisms for media playback (<audio> and <video>).

CSS Typed Object Model

A high-performance interface to styling elements. A fundamental building block that enables other "Houdini" features like CSS Custom Paint.

Not available for iOS.

CSS Containment

Features that enable consistently high performance in rendering UI, and a building block for new features that can dramatically improve performance on large pages and apps.

Not available for iOS.

CSS Motion Paths

Enables complex animations without JavaScript.

Not available for iOS.

Media Source API (a.k.a. "MSE")

MSE enables the MPEG-DASH video streaming protocol. Apple provides an implementation of HLS, but prevents use of alternatives.

Only available on iPadOS.

element.animate()

Browser support for the full Web Animations API has been rocky, with Chromium, Firefox, and Safari all completing support for the full spec the past year.

element.animate(), a subset of the full API, has enabled developers to more easily create high-performance visual effects with a lower risk of visual stuttering in Chrome and Firefox since 2014.

EventTarget Constructor

Seemingly trivial but deceptively foundational. Lets developers integrate with the browser's internal mechanism for message passing.

Delayed by nearly three years on iOS.

Web Performance APIs

iOS consistently fails to provide modern APIs for measuring web performance by three or more years. Delayed or missing features are not limited to:

• navigator.sendBeacon()
• Paint Timing (delayed two-to-four years)
• User Timing
• Resource Timing
• Performance Observers

The impact of missing Web Performance APIs is largely a question of scale: the larger the site or service one attempts to provide on the web, the more important measurement becomes.

fetch() and Streams

Modern, asynchronous network APIs that dramatically improve performance in some situations.

Delayed two to four years, depending on how one counts.

Not every feature blocked or delayed on iOS is transformative, and this list omits cases that were on the bubble (e.g., the 2.5 year lag for BigInt). Taken together, the delays Apple generates, even for low-controversy APIs, makes it challenging for businesses to treat the web as a serious development platform.

The Price #

Suppose Apple had implemented WebRTC and the Gamepad API in a timely way. Who can say if the game streaming revolution now taking place might have happened sooner? It's possible that Amazon Luna, NVIDIA GeForce NOW, Google Stadia, and Microsoft xCloud could have been built years earlier.

It's also possible that APIs delivered on every other platform, but not yet available on any iOS browser (because Apple), may unlock whole categories of experiences on the web.

While dozens of features are either currently, or predicted to be, delayed multiple years by Apple, a few high-impact capabilities deserve particular mention:

WebGL2

The first of two modern 3D graphics APIs currently held up by Apple, WebGL2 dramatically improves the visual fidelity of 3D applications on the web, including games. The underlying graphics capabilities from OpenGL ES 3.0 have been available in iOS since 2013 with iOS 7.0. WebGL 2 launched for other platforms on Chrome and Firefox in 2017. While WebGL2 is in development in WebKit, the anticipated end-to-end lag for these features is approaching half a decade.

WebGPU

WebGPU is a successor to WebGL and WebGL2 that improves graphics performance by better aligning with next-gen low-level graphics APIs (Vulkan, Direct3D 12, and Metal).

WebGPU will also unlock richer GPU compute for the web, accelerating machine learning and media applications. WebGPU is likely to ship in Chrome in late 2021. Despite years of delay in standards bodies at the behest of Apple engineers, the timeline for WebGPU on iOS is unclear. Keen observers anticipate a minimum of several years of additional delay.

WASM Threads and Shared Array Buffers

Web Assembly ("WASM") is supported by all browsers today, but extensions for "threading" (the ability to use multiple processor cores together) are missing from iOS.

Threading support enables richer and smoother 3D experiences, games, AR/VR apps, creative tools, simulations, and scientific computing. The history of this feature is complicated, but TL;DR, they are now available to sites that opt in on every platform save iOS. Worse, there's no timeline and little hope of them becoming available soon.

Combined with delays for Audio Worklets, modern graphics APIs, and Offscreen Canvas, many compelling reasons to own a device have been impossible to deliver on the web.^[11]

WebXR

Now in development in WebKit after years of radio silence, WebXR APIs provide Augmented Reality and Virtual Reality input and scene information to web applications. Combined with (delayed) advanced graphics APIs and threading support, WebXR enables immersive, low-friction commerce and entertainment on the web.

Support for a growing list of these features has been available in leading browsers across other platforms for several years. There is no timeline from Apple for when web developers can deliver equivalent experiences to their iOS users (in any browser).

These omissions mean web developers cannot compete with their native app counterparts on iOS in categories like gaming, shopping, and creative tools.

Developers expect some lag between the introduction of native features and corresponding browser APIs. Apple's policy against browser engine choice adds years of delays beyond the (expected) delay of design iteration, specification authoring, and browser feature development.

These delays prevent developers from reaching wealthy users with great experiences on the web. This gap, created exclusively and uniquely by Apple policy, all but forces businesses off the web and into the App Store where Apple prevents developers from reaching users with web experiences.

Just Out Of Reach #

One might imagine five-year delays for 3D, media, and games might be the worst impact of Apple's policies preventing browser engine progress. That would be mistaken.

The next tier of missing features is relatively uncontroversial proposals in development in standards groups that Apple participates in or has enough support from web developers to be "no-brainers". Each enables better quality web apps. None are expected on iOS any time soon:

Scroll Timeline for CSS & Web Animations

Likely to ship in Chromium later this year, enables smooth animation based on scrolling and swiping, a key interaction pattern on modern mobile devices.

No word from Apple on if or when this will be available to web developers on iOS.

content-visibility

CSS extensions that dramatically improve rendering performance for large pages and complex apps.

WASM SIMD

Coming to Chrome next month, WASM SIMD enables high performance vector math for dramatically improved performance for many media, ML, and 3D applications.

Form-associated Web Components

Reduces data loss in web forms and enables components to be easily reused across projects and sites.

CSS Custom Paint

Efficiently enables new styles of drawing content on the web, removing many hard tradeoffs between visual richness, accessibility, and performance.

Trusted Types

A standard version of an approach demonstrated in Google's web applications to dramatically improve security.

CSS Container Queries

A top request from web developers and expected in Chrome later this year, CSS Container Queries enable content to better adapt to varying device form-factors.

<dialog>

A built-in mechanism for a common UI pattern, improving performance and consistency.

inert Attribute

Improves focus management and accessibility.

Browser assisted lazy-loading

Reduces data use and improves page load performance.

Fewer of these features are foundational (e.g. SIMD). However, even those that can be emulated in other ways still impose costs on developers and iOS users to paper over the gaps in Apple's implementation of the web platform. This tax can, without great care, slow experiences for users on other platforms as well^[12].

What Could Be #

Beyond these relatively uncontroversial (MIA) features lies an ocean of foreclosed possibility. Were Apple willing to allow the sort of honest browser competition for iOS that MacOS users enjoy, features like these would enable entirely new classes of web applications. Perhaps that's the problem.

Some crucial features (shipped on every other OS) that Apple is preventing any browser from delivering to iOS today, in no particular order:

Push Notifications

In an egregious display of anti-web gate-keeping, Apple has implemented for iOS neither the long-standard Web Push API nor Apple's own, entirely proprietary push notification system for MacOS Safari

It's difficult to overstate the challenges posed by a lack of push notifications on a modern mobile platform. Developers across categories report a lack of push notifications as a deal-killer, including:

• Chat, messaging, and social apps (for obvious reasons)
• e-commerce (abandoned cart reminders, shipping updates, etc.)
• News publishers (breaking news alerts)
• Travel (itinerary updates & at-a-glance info)
• Ride sharing & delivery (status updates)

This omission has put sand in the web's tank — to the benefit of Apple's native platform, which has enjoyed push notification support for 12 years.

PWA Install Prompts

Apple led the way with support for installing certain web apps to a device's homescreen as early as iOS 1.0. Since 2007, support for these features has barely improved.

Subsequently, Apple added the ability to promote the installation of native apps, but has not provided equivalent "install prompt" tools for web apps.

Meanwhile, browsers on other platforms have developed both ambient (browser provided) promotion and programmatic mechanisms to guide users in saving frequently-used web content to their devices.

Apple's maintenance of this feature gap between native and web (despite clear underlying support for the mechanism) and unwillingness to allow other iOS browsers to improve the situation^[13], combined with policies that prevent the placement of web content in the App Store, puts a heavy thumb on the scale for discovering content built with Apple's proprietary APIs.

PWA App Icon Badging

Provides support for "unread counts", e.g. for email and chat programs. Not available for web apps added to the home screen on iOS.

Media Session API

Enables web apps to play media while in the background. It also allows developers to plug into (and configure) system controls for back/forward/play/pause/etc. and provide track metadata (title, album, cover art).

Lack of this feature prevents entire classes of media applications (podcasting and music apps like Spotify) from being plausible.

In development now, but if it ships this fall (the earliest window), web media apps will have been delayed more than five years.

Navigation Preloads

Dramatically improve page loading performance on sites that provide an offline experience using Service Workers.

Multiple top-10 web properties have reported to Apple that lack of this feature prevents them from deploying more resilient versions of their experiences (including building PWAs) for users on iOS.

Offscreen Canvas

Improves the smoothness of 3D and media applications by moving rendering work to a separate thread. For latency-sensitive use-cases like XR and games, this feature is necessary to consistently deliver a competitive experience.

TextEncoderStream & TextDecoderStream

These TransformStream types help applications efficiently deal with large amounts of binary data. They may have shipped in iOS 14.5 but the release notes are ambiguious.

requestVideoFrameCallback()

Helps media apps on the web save battery when doing video processing.

Compression Streams

Enable developers to compress data efficiently without downloading large amounts of code to the browser.

Keyboard Lock API

An essential part of remote desktop apps and some game streaming scenarios with keyboards attached (not uncommon for iPadOS users).

Declarative Shadow DOM

An addition to the Web Components system that powers applications like YouTube and Apple Music. Declarative Shadow DOM can improve loading performance and help developers provide UI for users when scripts are disabled or fail to load.

Reporting API

Indispensable for improving the quality of sites and avoid breakage due to browser deprecations. Modern versions also let developers know when applications crash, helping them diagnose and repair broken sites.

Permissions API

Helps developers present better, more contextual options and prompts, reducing user annoyance and "prompt spam".

Screen Wakelock

Keeps the screen from going dark or a screen saver taking over. Important for apps that present boarding passes and QR codes for scanning, as well as and presentation apps (e.g. PowerPoint or Google Slides).

Intersection Observer V2

Reduces ad fraud and enables one-tap-sign-up flows, improving commerce conversion rates.

Content Indexing

An extension to Service Workers that enables browsers to present users with cached content when offline.

AV1/AVIF

A modern, royalty-free video codec with near-universal support outside Safari.

PWA App Shortcuts

Allows developers to configure "long press" or "right-click" options for web apps installed to the home screen or dock.

Shared Workers and Broadcast Channels

Coordination APIs allow applications to save memory and processing power (albeit, most often in desktop and tablet form-factors).

getInstalledRelatedApps()

Helps developers avoid prompting users for permissions that might be duplicative with apps already on the system. Particularly important for avoiding duplicated push notifications.

Background Sync

A tool for reliably sending data — for example, chat and email messages — in the face of intermittent network connections.

Background Fetch API

Allows applications to upload and download bulk media efficiently with progress indicators and controls. Important for reliably syncing playlists of music or videos for offline or synchronising photos/media for sharing.

Periodic Background Sync

Helps applications ensure they have fresh content to display offline in a battery and bandwidth-sensitive way.

Web Share Target

Allows installed web apps to receive sharing intents via system UI, enabling chat and social media apps to help users post content more easily.

The list of missing, foundational APIs for media, social, e-commerce, 3d apps, and games is astonishing. Essential apps in the most popular categories in the App Store are impossible to attempt on the web on iOS because of feature gaps Apple has created and perpetuates.

Device APIs: The Final Frontier #

An area where browsers makers disagree fervently, but where Chromium-based browsers have forged ahead (Chrome, Edge, Samsung Internet, Opera, UC, etc.) is access to hardware devices. While not essential to most "traditional" web apps, these features are foundational for vibrant categories like education and creative music applications. iOS Safari supports none of them today, while Chromium browsers on other OSes enable these apps on the web:

Web Bluetooth

Allows Bluetooth Low Energy devices to safely communicate with web apps, eliminating the need to download heavyweight applications to configure individual IoT devices.

Web MIDI

Enables creative music applications on the web, including synthesisers, mixing suites, drum machines, and music recording.

Web USB

Provides safe access to USB devices from the web, enabling new classes of applications in the browser from education to software development and debugging.

Web Serial

Supports connections to legacy devices. Particularly important in industrial, IoT, health care, and education scenarios.

Web Serial, Web Bluetooth, and Web USB enable educational programming tools to help students learn to program physical devices, including LEGO.

Independent developer Henrik Jorteg has written at length about frustration stemming from an inability to access these features on iOS, and has testified to the way they enable lower cost development. The lack of web APIs on iOS isn't just a frustration for developers. It drives up the prices of goods and services, shrinking the number of organisations that can deliver them.

Web HID

Enables safe connection to input devices not traditionally supported as keyboards, mice, or gamepads.

This API provides safe access to specialised features of niche hardware over a standard protocol they already support without proprietary software or unsafe native binary downloads.

Web NFC

Lets web apps safely read and write NFC tags, e.g. for tap-to-pay applications.

Shape Detection

Unlocks platform and OS provided capabilities for high-performance recognition of barcodes, faces, text in images and video.

Important in videoconferencing, commerce, and IoT setup scenarios.

Generic Sensors API

A uniform API for accessing sensors standard in phones, including Gyroscopes, Proximity sensors, Device Orientation, Acceleration sensors, Gravity sensors, and Ambient Light detectors.

Each entry in this inexhaustive list can block entire classes of applications from credibly being possible on the web. The real-world impact is challenging to measure. Weighing up the deadweight losses seems a good angle for economists to investigate. Start-ups not attempted, services not built, and higher prices for businesses forced to develop native apps multiple times could, perhaps, be estimated.

Incongruous #

The data agree: Apple's web engine consistently trails others in both compatibility and features, resulting in a large and persistent gap with Apple's native platform.

Apple wishes us to accept that:

• It is reasonable to force iOS browsers to use its web engine, leaving iOS on the trailing edge.
• The web is a viable alternative on iOS for developers unhappy with App Store policies.

One or the other might be reasonable. Together? Hmm.

Parties interested in the health of the digital ecosystem should look past Apple's claims and focus on the differential pace of progress.

Full disclosure: for the past twelve years I have worked on Chromium at Google, spanning both the pre-fork era where potential features for Chrome and Safari were discussed within the WebKit project, as well as the post-fork epoch. Over this time I have led multiple projects to add features to the web, some of which have been opposed by Safari engineers.

Today, I lead Project Fugu, a collaboration within Chromium that is directly responsible for the majority of the device APIs mentioned above. Microsoft, Intel, Google, Samsung, and others are contributing to this work, and it is being done in the open with the hope of standardisation, but my interest in its success is large. My front-row seat allows me to state unequivocally that independent software developers are clamouring for these APIs and are ignored when they request support for them from Apple. It is personally frustrating to be unable to deliver these improvements for developers who wish to reach iOS users — which is all developers. My interests and biases are plain.

Previously, I helped lead the effort to develop Service Workers, Push Notifications, and PWAs over the frequent and pointed objections of Apple's engineers and managers. Service Worker design was started as a collaboration between Google, Mozilla, Samsung, Facebook, Microsoft, and independent developers looking to make better, more reliable web applications. Apple only joined the group after other web engines had delivered working implementations. The delay in availability of Service Workers (as well as highly-requested follow-on features like Navigation Preload) for iOS users and developers interested in serving them well, likewise, carries an undeniable personal burden of memory.