Infrequently Noted

Update (September 25th, 2021): Commenters appear confused about Apple's many options to ensure safety in a world of true browser competition, JITs and all. This post has been expanded to more clearly enunciate a few of these alternatives.

Update (April 29th, 2022): Since this post was first published, Google's Project Zero released an overview regarding browser security trends. This post has been updated to capture their finding that iOS and Safari continues to lag the industry in delivering fixes to issues that Project Zero finds.

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 and compatible than they are on every other platform.

How does Apple justify such a policy? Particularly since last winter, when it finally (ham-fistedly, 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 recently and only when compelled:

• 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 this skepticism is expressed in technical terms that can obscure deeper issues. Apple's response to the U.S. House Antitrust Subcommittee includes its fullest response and it provides a helpful, less-technical framing to discuss how browser engine choice relates to power over software distribution:

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.

Let's address 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 have the freedom to distribute modified binaries, WebKit's source code can serve as the basis for new engines. Anyone can fork WebKit and improve it, but they cannot ship enhancements to iOS users of their products.

Apple asserts this is fine becase WebKit's openness extends to open governance regarding feature additions. It must know this is misleading.

Presumably, Apple's counsel included this specious filigree to distract from the reality that Apple rarely accepts outside changes that push the state of the art forward. Here I speak from experience.

From 2008 to 2013, the Chromium project was based on WebKit, and a growing team of Chrome engineers began to contribute heavily "upstream." I helped lead the team that developed Web Components. Our difficulty in trying to develop these features in WebKit cannot be overstated. The eventual Blink fork was precipitated by an insurmountable difficulty in doing precisely what Apple suggested to Congress: contributing new features to WebKit.

The differing near-term objectives of browser teams often make potential additions contentious, and only competition has been shown to reliably drive consensus. Every team has more than enough to do, and time spent even considering new features can be seen as a distraction. Project owners fiercely guard the integrity of their codebases. Until and unless they become convinced of the utility of a feature, "no" is the usual response. If there is no competition to force the issue, it can also be the final answer.

Browser engines are large projects, necessitating governance through senior engineer code review. There tend to be very few experts empowered to do reviews in each area relative to number of engineers contributing code.

It's inevitable that managers will communicate disinterest in continuing collaboration if they find their most senior engineers spending a great deal of time reviewing code for features they have no interest in and will disable ("flag off") in their own products^[2]. The pace of code reviews needed to finish a feature in this state can taper off or dry up completely, frustrating collaborators on both sides.

When browsers provide their own engines (an "integrated browser"), then it's possible to disagree in standards venues, return to one's corner, and deliver their best design to developers (responsibly, hopefully). Developers can then provide feedback and lobby other vendors 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, pre-emptively "decline to implement" a veritable truckload features that some vendors feel are essential and would be willing to ship in their products.

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

Suppose by some miracle a "controversial" feature is merged into WebKit. This is no gaurantee that iOS browsers will gain access to it. Features in this state have lingered behind flags for years, ensuring they are not available in either Safari or competing iOS browsers.

When priority disagreements inevitably arise, competing iOS browsers cannot reliably demonstrate a feature is safe or well received by web developers by contributing to WebKit. Potential sponsors of this work won't dare the expense of an attempt. Apple's opacity and history of challenging collaboration have done more than enough to discourage ambitious participants.

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

It is shocking, but unsurprising, that Apple felt compelled to mislead Congress on these points. The facts are not in their favour, but few legislative staffers have enough context to see through debates about browser internals.

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 and aggressive mitigations in their first lines of defence, in addition to more strictly isolating individual websites from each other. None of these protections were in place for iOS users in the most recent Solar Winds incident thanks to Apple's policy against engine choice, even for folks using browsers other than Safari.

The incredibly powerful devices Apple sells provide more than enough resources to raise such software defences, yet iOS users are years behind in recieving them and can't access them by switching browser. Apple's under-investment in security combine with its uniquely anti-competitive polices to ensure these gaps cannot be filled, no matter how contientious iOS users are about their digital hygiene.

Leading browsers are also adopting more robust processes for closing the "patch gap". Since all engines 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. Cupertino's industry-lagging pace in adding additional layers of defence do not inspire confidence, either.

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 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 Chrome OS's status quo seem a defence of iOS, know that 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!

Lower-friction updates lead to faster patch application, keeping users safer, and Chrome OS is miles ahead of iOS in this regard.

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

This makes intuitive sense: iOS update downloads are large and installing them can disrupt using a device for as much as a half hour. Users are understandably hesitant to incur these interruptions. Browser updates delivered out-of-band can be smaller and faster to apply, often without 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 for Apple in terms of staffing. 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.

Preventable insecurity, iOS be thy name.

Update: In February 2022, Google's Project Zero posted a report on the metrics they track regarding product bug and patch rates. This included a section on browsers, which included the following — incredibly damning — chart:

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 these additional features.

More troublingly, these features are built in a way that is different to the mechanisms used by browser teams on every other platform. Any browser that delivers a feature to other platforms, then tries to bring it to iOS through script extensions, has doubled the security analysis and attack surface area.

None of this is theoretical; needing to re-develop features through a straw, using less-secure, more poorly tested and analyzed mechanisms, has led to serious security issues in alternative iOS browsers. 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 Apple's 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 had 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 do learn about them, but at the greatest of delays.

Policy Options #

Apple may genuinely believe it is improving security by preventing other engines, not just padding its bottom line. For instance, beyond the abandonware problem, what of threats from "legitimate" browsers that abuse JIT priviledges? Or vendors that drag their heels in responding to security issues?

No OS vendor wants third parties exposing users to risks it feels helpless to mitigate. Removing browsers from user's devices is an existing option, but would be a drastic step that raises serious governance questions about the power Apple wields (and on whose behalf).

As middle-ground policy options go, Apple is far from helpless.

It has already created a bright line between browsers and other apps that embed WebViews, thanks to the Browser Entitlement, and could continue to require the latter use Apple's system-provided WebKit.

For browsers slow to fix security bugs, there also options short of dissalowing other engines and their JITs. Every engine on the market today also contains a non-JITing mode. Apple could require that vendors submit both JITful and JITless builds for each version they wish to publish and could, as a matter of policy and with warning, update user devices with non-JITing versions of these browsers should users be opened to widespread attack through vendor negligence.

In the process of opening up the necessary private APIs to build truly competitive browsers, Apple can set design quality standards. For example, if Apple's engine uses a now-private mechanism to ensure that code pages are not both writeable and executable, it could require other engines adopt the same techniques. Apple could further compel vendors to aggressively adopt protections from new hardware capabilities (e.g. Control Flow Integrity (pdf)) as it releases them.

Lastly, Apple can mandate all code loaded into sandboxed renderer processes be published as open source, along with build configurations, so that Apple can verify the supply chain integrity of browsers granted these capabilities.

Apple can maintain protections for users in the face of competition. Hiding behind security concerns to deny its users access to better, safer, faster browsers is indefensible.

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 engine 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 meaningfully advance the state of the art.

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.

Taxation of software occurs through re-privatisation of low-level, standards-based features and APIs. By restricting use of previously-free features (e.g. Bluetooth, USB, Serial, MIDI, and HID) to proprietary frameworks and distribution channels, a successful would-be monopolist can extract outsized rents on any application that requires even one of these features. Impoverishing the commons through delay and obstruction is, over time, indistinguishable from active demolition.

Apple's playbook is in line with this diagnosis, preserving the commons as a historical curiosity at best. 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 over short time horizons. Disallowing competitive engines may have been accidental at introduction of iOS, but its value to Apple now cannot be overstated. After all, it's hard to extract ruinous taxes on a restive population with straightforward emigration options. No wonder Cupertino continues to put on 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. This commons allows services to be built without taxation; but only to the extent it's capable enough to meet user and developer needs over time.

Continuous integration of previouly-proprietary features into the commons is the mechanism by which progress is delivered. Push notifications may have been 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, or more efficient codecs.

The sorts of diversity we have come to value in the web ecosystem exist exclusively at the leading edge.

Intense disputes about the best ways to standardise 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 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.

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

It's a curious argument.

In the first instance, it admits that Apple's engine is deeply sub-par, failing to achieve the level of quality that even Mozilla's investments have produced. Having given up the core claim of product superiority, this failure is rhetorically pivoted into a defense of the ongoing failure to compete: because Apple's product is bad, it shouldn't be forced to allow competition, as people might then choose better products.^[5]

Apple is not lacking funds or talent to build a competitive product, 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 not much of a defence. Excusing poor performance is to suggest that Apple does not possess the talent, skill, and resources to ever construct a competitive engine. I, at least, think better of Apple's engineering acumen than these nominal defenders.

Would WebKit really dissapear if Apple were to allow other engines onto iOS? We have a natural experiment in Safari for macOS. It continues to enjoy a high share of that browser market despite stiff and competition from browsers that include higher-quality engines. Why are Apple's defenders so certain that this won't be the result for iOS?

And what is the worst-case scenario, exactly?

That Safari loses share such that 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.

It's not a foregone conclusion the world's most valuable tech firm must produce the lowest-quality browser and externalise huge costs onto developers and users. Developer's might even take Apple's side if coercion about engine choice weren't paired with failure to keep pace on even basic features.

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.

Update: This post was turned into a talk for State of The Browser in October 2021; you can watch the recording here.

Update, The Second: Welp, I was wrong. I assumed that Facebook PMs and engineers were smart. Of course they were going to get found out modifying content via In-App Browsers, just as this post warned they could. It's long past time for Google and Apple to act to curb this abuse via App Store policy, and regulators interested in gatekeeper shenanigans should take notice.

The post has also been updated for readability and to more clearly outline the previously-embedded per-page opt-out proposal.

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 are generally older and wealthier than the median user and likely formed expectations of browsers on the desktop. They may, therefore, tend to think about mobile browser competition through the lends of desktop browsing. To recap:

• Users can freely choose desktop browsers with differing UIs, 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 progress.

The mobile ecosystem appears to retain these properties, but the resemblance is only skin deep. Understanding how mobile OSes undermine browser choice requires an 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 to know that competitors are still prevented from using their own browser engines.

Meanwhile, the #2 and #3 sources of web traffic on Android — Google's search box and Facebook's native apps — 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 be the user's agent, it must also receive navigations. Google's Search App and Facebook's apps undermine these choices in slightly different ways.^[3] This defangs the privacy and security choices made through browsers. Developers suffer higher costs when they cannot escape Google, Facebook, and Apple's walled gardens or effectively reach users through the web.

Web engineers frequently refer to browsers as "User Agents", a nod to their unique role in giving users the final say over how the web is experienced. A silent erosion of browser choice has transferred power away from users, depositing it with dominant platforms and apps. To understand how this sell-out happened under our noses, literally, let's look at how mobile and desktop differ.

The Baseline Scenario #

The predominant desktop situation is straightforward:

Browsers handle links, and non-browsers defer loading http and https URLs to the system, which in turn invokes the user's default browser. This flow is what gives links utility. If the players involved (OSes, browsers, or referring apps) violate aspects of the contract, user choice in browsers has less effect.

"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 manifest intent filters and 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 facilitates browser choice, it's this ability to replace the default handler for links that defines browsers. How often links lead users to their browser defines the meaningfulness of this choice.

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

Mobile browsers started in a remarkably resource-constrained environment. First-generation iOS and Android smartphones were slow single-core, memory-impoverished affairs, leading mobile OSes to adopt heuristics for killing background apps to reclaim memory. This helped ensure the whole system remained responsive.

But background task killing created problems for link-heavy apps. Launching the browser placed linking apps in the background and browser UI didn't provide affordances for returning to referring applications. This reduced the probability users would return, hurting engagement.

Being put in the background also increased the likelihood of a linking app being killed.^[5] It can take seconds to re-start the original app and restore UI state, an experience that gets worse on low-end devices that are most likely to evict apps in the first place.

To compensate, engagement-thirsty apps began including "In-App Browsers" ("IABs") to keep links from bouncing users to browsers. Contrary to any plain-language understanding of "a browser", these IABs cannot be installed as browsers, even where OSes enabled 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.
• WebViews allow embedders to observe and modify network traffic (regardless of encryption).
• WebViews can monitor user input, passwords, site content, and system auto-filled credentials.

In the unlikely scenario users are happy for browsers to forget their saved passwords, login state, privacy preferences, extensions, and accessibility settings, this could, in theory, be a win-win. In practice it is a hidden, ecosystem-wide tax.

IABs are hard to spot unless you know exactly what you're looking for, and the controls to disable them are consistently buried in hard-to-find UI. The cumulative result is that tapping links generally feels broken.^[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 use of WebViews in non-browser apps is appropriate for first and second-party content. Here, apps are either rendering their own web content or the content can be expected to know about the limits imposed by the WebView implementation. Instead of breaking content, WebViews rendering first and second party content can help apps deliver better experiences without additional privacy and security concerns.

All bets are off regarding WebViews and third-party content. Remember, WebViews are not browsers.

WebViews support core features for rendering web content, along with hooks that allow embedders to "light up" permission-based APIs (e.g., webcam access). Making a full browser out of a WebView requires a lot of additional UI and glue code.

Features that need extra care to support 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 underlying system WebViews provide the right hooks.

The situation is even more acute in WebView IABs, where features are often broken even when they appear to be available to developers. Debugging content in IAB franken-browsers is challenging, and web developers are often blind to the volume of traffic they generate, meaning they may not even understand how broken their experiences are.

How can that be? Web developers are accustomed to real browsers and industry standard tools, analytics, and feature dashboards do break out or highlight IABs. The biggest IAB promulgators (Facebook, Pinterest, Snap, etc.) are complicit, investing nothing in clarifying the situation.

Neither users nor developers understand Facebook, Pinterest, or Google Go as browsers. If they did, they would be livid at the poor quality and broken feature set. WebView IABs strip users of choice, and technical limits they impose prevent web developers from any recourse to real browsers.

No documentation is available for third-party web developers from any of the largest WebView IAB makers. This scandalous free-riding is shady, but not surprising. It is, however, all the more egregious for the subtlety and scale of breakage.

Thanks to IAB shenanigans, Facebook is the third largest Android "browser"-maker. If it 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.

Update (Oct '21): How feature-deprived are WebView IABs? Several months after this post was published, and with no apparent irony, Facebook dropped support for WebViews as a login mechanism to Facebook itself. That's right, Facebook's own app is now an unsupported browser for the purposes of logging in to Facebook.

WebView IAB makers have been given "the first 80%" of a browser. Development and distribution of critical components is also subsidised by OS vendors. Despite these considerable advantages, WebView IABs universally fail to keep up their end of the bargain.

First-party developers can collaborate with their IAB colleagues to build custom access to any feature they need.

Likewise, second-party developers expect less and their content will not appear to be broken — ads are generally not given broad feature access.

But third-party developers? They are helpless to understand why an otherwise browser-presenting environment is 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. +

49 05:12 AM · 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 takes users to their browser, assuming they are not already in a browsesr. If a link from an email application points to example.com, previous login state and passwords are not forgotten. Saved addresses and payment information are readily available, speeding up checkout flows. Most importantly, accessibility settings and privacy preferences are consistently applied.

By contrast, WebView IABs fracture state, storing it in silos within each application. This creates a continuous partial amnesia, where privacy settings, accessibility options, passwords, logins, and app state are frequently lost.

The resulting confusion doesn't hurt apps that foist WebView IABs on unsuspecting users and developers. The costs are borne by publishers and users, harming the larger web ecosystem. IABs are, in this understanding, a negative externality.

Does anyone expect anything one does on a website loaded from a link within Facebook, Instagram, or Google Go can be monitored by those apps? That passwords can be collected? That all sites you visit can be 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. (August '22) Facebook has been caught red-handed absuing this power to track users within their IAB browser without explicit consent. Sanctions, App Store policies, and opt-out mechanisms are overdue.

The WebView IAB sleight of hand is to act as a browser when users least expect it, but never to cop to the privacy implications of silently undermining user choice.

CCT: A New Hope? #

As libraries emerged to facilitate the construction of WebView IABs, OS and browser vendors belated became aware that users were becoming confused and that web publishers were anguished about the way that social media apps broke login state.

To address this challenge, Apple introduced SFSafariViewController ("SFSVC")^[9] and Google followed suit with Chrome Custom Tabs protocol ("CCT"). Both systems let native apps to skip the work of building WebView IABs and, instead, provide an OS-wide mechanism for invoking the user's default browser over top of a native app.

Like 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. They also provide the complete set of features supported by the user's default browser, improving business outcomes for web publishers.

These solutions come at the cost of flexibility for app developers who lose access to snoop on page content, read network traffic, or inject custom behavior. Frustratingly, no OS or App Store mandate their use for IAB needs. More on this shortly.

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 (ada@mastodon.social) @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.

6 11:21 AM · 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.

Early on, there were justifiable reasons to hard-code Chrome. Before support for CCT was widespread, some browsers exhibited showstopper bugs.

Fast-forward to 2021 and those bugs are long gone, but the hard-coding persists. Today, the primary effect is to distort the market for browsers and undermine user choice. This subverts privacy and makes it hard for alternative browsers to compete on a level playing field.

This is admittedly better than the wholesale neutering of important features by WebView IABs, but when users change browsers, continuious partial amnesia on the web gets worse. A Hobson's Choice of browser.

WebLayer: New Frontiers In User Confusion #

Google can (and should) revert to CCT's default behavior which respects user choice. Since AGSA uses CCT to load web pages rather than a WebView, this would be a nearly trivial code change. CCT's core design is sound and has enormous potential if made mandatory in place of WebView IABs. The Android and Play teams could mandate better behavior in IABs to improve user privacy.

There's reason to worry that this is unlikely.

Instead of addressing frequent developer requests for features in the CCT library, the Chrome 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 weakly positive case for WebLayer. For folks making browsers, WebLayer dramatically reduces the amount of custom glue code needed to light up adavanced features. In the context of IABs, however, WebLayer looks set to entrench user-hostile patterns even further.

Subversion of choice is a dispiriting trend in search apps. Stealing traffic without any effort to honestly earn a spot as the user's preferred browser is, at best, uncouth and adopting WebLayer will not meaningfully improve the user experience or privacy of these amnesiac browsing experiences.

Google Go, the Google app for iOS, and Microsoft's Bing app for Android all capture outbound links in WebView IABs, subverting browser choice and rubbishing features for developers. If there's any mercy, it's that their low use limits the impact on the ecosystem.

Google and Apple could prevent this bad behavior through App Store policies and technical changes. They have the chance to lead, to show they aren't user-hostile, and remove a 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. With the wrong engine, many jobs cannot be done, rendering whole classes of vehicles pointless. If the mandated engine were particularly polluting, choosing a different model would have little effect on emissions.

That's the situation iOS creates regarding browsers today. The only recourse it to buy a phone running a different OS.

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.

Bosses, board memebers, and tech reviewers all live in the iOS ecosystem. Because Apple prevents better web engines anywhere on its platform, browser choice is hollow.

Apple has deigned to allow "browsers" in its App Store since 2012. Those apps could not be browsers in a meaningful sense because they could not replace Safari as the default handler for http/https links.

The decade-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 care to ensure that choice is only skin deep. Browsers on Windows, Linux, ChromeOS, Android, and MacOS can be Integrated Browsers, including their own competing engines. 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 if it also kept other native apps from accessing powerful features. Such policies would represent a different view of what computing should be. However, Apple is happy to provide a wide variety of scary features to unsafe native applications, so long as they comply with the coercive terms of its App Store.

Powerful browsers present a threat to the fundamentals of Apple and Google's whale-based, dopamine fueled, "casual" gaming monetisation rackets.

Unlike other native apps, browsers are principally concerned with user safety. A safe-by-default, capable platform with low-friction discovery could obviate the root justification for app stores: that they keep over-powered native apps in check.

Apple forestalls this threat by keeping the web on iOS from feature parity. Outlawing true 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 (ada@mastodon.social) @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

676 11:05 AM · May 4, 2021

Ada Rose Cannon (ada@mastodon.social) @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.

152 11:05 AM · May 4, 2021

Ada Rose Cannon (ada@mastodon.social) @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.

152 11:10 AM · May 4, 2021

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

Hollowing out choice while starving Safari and WebKit of resources managed to 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 conformanc". While Apple's engine falls woefully short on support for basic 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, developers must spend more to work around these limitations. When important APIs go missing, 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 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 choice in browsers leads directly to higher costs for users and developers across the mobile ecosystem even for folks that don't use Apple's products. Apple's norm-eroding policies have created a permission struture for bad actors like Facebook. Apple's leadership in the race to the bottom has inspired a burgeoning field of fast-followers.

Browser choice is not unrelated to other objectionable App Store policies. Keeping the web from competing is part and parcel of an architecture of control that tilts commerce into coercive, centralising stores, even though safer, browser-based alternatives would otherwise be possible.

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 the situation must centre on the effectiveness of browser choice.

Some policymakers have suggested browser choice ballots, but these will not be effective if user choice is undermined no matter which browser they choose. Interventions that encourage brand-level choice cannot have a positive effect until the deeper positive impacts of choice are 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.

Don't WebView Me Bro! #

The proposal for a header to allow sites to demand CCT/SFSVC instead of a WebView IAB may seem complex, but it is technically straightforward and can be implemented very quickly.

Websites would include a tag (or the equivalent HTTP header) in top-level pages like this:

  <meta http-equiv="Content-Security-Policy"
        content="frame-ancestors 'system-default'">

OS vendors would update their system WebViews to respect this tag and invoke CCT if encountered in a top-level document. This is compatible with the existing ecosystem, as no first-party content (help pages) or second-party integration (ad network) would send these headers, existing apps would not need to be updated. Websites could incrementally add the hint and benefit from the new behavior.

Android's WebView component auto-updates with Chrome, ensuring huge reach for such a fix in a short time. iOS updates are fused to OS upgrades, but iOS users tend to upgrade quickly. The net effect is that we should expect such a policy to begin to have a large, positive effect in less than 6 months.

What about apps that try to subvert the default behavior? App store policies can be easily formulated to punish this sort of poor behavior. There's a great deal of evidence that these policies work, at least for the "head" of an app catalog, and would surely condition Facebook's behavior.

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

##
# *Update* (2021-09-18): OPTIONAL
#
#     If your repo is going to make use of Git LFS, at 
#     this point you should stop and edit `.bare/config` 
#     so that the `[remote "origin"]` section reads as:
#
#     [remote "origin"]
#             url = git@github.com:example/workit.git
#             fetch = +refs/heads/*:refs/remotes/origin/*
#
#     This ensures that new worktrees do not attempt to 
#     re-upload every resource on first push.
##       

##
# 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.

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

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] and allow competition. They are, pound for pound, some of the best engine developers 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, 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. Performance Measurement is easy to get wrong. Spurious reports of "10x worse" performance merit intense scepticism, as they tend instead to be mismeasurement. This makes sense given the intense focus of all browser teams on performance.

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. Still, mistakes have been made, and 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.

Update: some commenters seem to sneer the the idea of using a mouse for gaming on iOS, but it has been reported to browser teams as a key feature by the teams building game streaming PWAs. It appears a sizeable set of users use external mice and keyboards with their iPads, and the entire categories of games are functionally unusable on these platforms without Pointer Lock.

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 more than 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).

Supported only for use in WebRTC but not the usual mechanisms for media playback (<audio> and <video>). Either delayed 9 years or still not available, depending on use.

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 contains relatively uncontroversial proposals from standards groups that Apple participates in or which have 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.