At least Firefox will still have it, although with Mozilla being the way that it is, I wouldn't be surprised if they follow suit.
I feel the same way about this that I do about removing Flash support: it's good that we're moving on to better things, but that doesn't help if there aren't better things to move on to.
What's the simple goto for making web based games that kids can mess around with? It was Flash, and now it's nothing. How do you set up an RSS feed to not just blast raw XML at the user? Soon it won't be XSLT any more, but I don't see a good replacement (even more annoying is the fact that browsers used to have features to handle RSS feeds by themselves, and XSLT was used to sidestep that problem, but now there's no more side to step).
When I first learned that XSLT was going away, I got curious how to achieve the same thing in JS (client-side templating that happens during page load, without any "flash of content"). It turns out there's a very nice way to do it, by using inline scripts that append elements next to document.currentScript. Lean Rada wrote about it here: https://leanrada.com/notes/inline-rendering-currentscript/ and I wrote about it as well: https://vladimirslepnev.me/write
I am still using XSLT. I have been using it for 26 years. I generate XML documents on the backend and turn them into HTML for various reports. XSLT has a lot of features and power that newer templating languages lack.
Are any of these newer templating languages worth me switching?
Their comment isn’t clear if they’re doing the transform on the server before piping it down as HTML, which some implementations have done over the years as it provided access to newer XSLT features that browsers stagnated on.
Flash went away because Steve Jobs made an impassioned plea to find a better way and follow their humble browser which only had single digit percentages of marketshare at the time.
Even for enthusiastic Android vendors who saw it as a differentiating feature from iPhone, Flash still took three years from the iPhone launch to have its first release. Adobe was really in poor shape to port Flash to a new platform. Waiting for them as a vendor to bump their proprietary platform vs integrating support for the features into the browser would have cost years for mobile adoption.
> Adobe was really in poor shape to port Flash to a new platform
I wouldn't say poor. Adobe had its own creative-software empire to up-keep. Photoshop, Illustrator, After Effects, and its web-authoring products gave it enormous influence over creative professionals. Macromedia's Dreamweaver and Flash were serious competitors in web design and interactive media. Adobe needed the missing monopoly cards; Flash, Fireworks and Dreamweaver were them.
Flash was security ridden yes, Flash required a plugin, yes; I don't think supported AppleOS at the time. These could of all been solved but I would agree that to refactor the software would of been an expensive take.
Jobs + HTML5, WebGL, JS all had entered the ring and finished the blow.
I miss it. Growing up with the internet in 2003, 2010's was the end of the wild world web. 2020's was the era of walled gardens for which we now have LLM's for the theme park and we're now entering 2030 where the internet is on fire with creativity now wrung between Yes Ai and No Ai.
Domain name:
lordsephiroth.co.uk
Relevant dates:
Registered on: 18-Nov-2003
My first ever domain name, registered with my pocket money at the age of 13. Hopefully 2040 should bring world peace. One would hope.
Flash went away because Steve Jobs made an impassioned plea to find a better way and follow their humble browser which only had single digit percentages of marketshare at the time.
You're half right.
Yes, Jobs killed Flash. But he did it because Flash on mobile was a battery killer. And when the original iPhone came out (one of which I still have), battery technology wasn't as advanced as it is now.
Before I got my wife's hand-me-down iPhone, I had one of the few mobile phones that supported Flash. On the few occasions when I used the web browser, I lived in fear that I'd land on a web site that was using Flash because I knew it would tear through the phone's battery in less than 10 minutes.
Ever notice that the people on HN who pine for the good-ol'-days of Flash only remember games? Never the Flash ads and intrusive videos.
Yes and no, canvas was fine for replacing flash, and JS performance was good enough quickly.
Audio however was a crapshoot for years, especially for games.
Even basic WebAudio took until 2015, and the final piece to match Flash being AudioWorklet was only first available in 2018(Chrome) and took until April _2021_ land in Safari.
So before 2021 you needed to either write your own abstractions to support multiple API's with different execution models with so-so capabilties to be somewhat on-par with what Flash provided or even for years resort to simpler solutions (ie just samples).
I find it baffling that anyone still cares. RSS nerds like RSS because it can be consumed by software that displays it however the user wants. XSLT pages just function as normal webpages, there is no consuming it programatically because XSLT is the view language. The underlying XML/RSS is what you wanted, not the hodgepodged together crap on top of it.
Shame back in the XHTML days XSLT was a spec that could have made website modularity so much cleaner. I once created an early website creation tool that merged separate components using XSLT it was really powerful in the days before javascript was usable without jQuery. However XHTML was dropped in favor of HTML5 and XSLT was pretty much useless after that. Its done well to survive this long I presume it was mainly kept to style XML files.
HTML5 could have taken the extra step of defining a canonical XML or XML-compatible DOM encoding, or at least encouraged it. But the anti-XML sentiment was explicit and spiteful. Still, popular XSLT processors are built to consume and even produce HTML5, I'm just not sure how thorough those capabilities are or whether they're based on any formal or informal standards. (Maybe the W3C has/had something like that, as part of it's attempts to rollup HTML5 snapshots into versioned standards?)
I lost any enthusiasm for XML after my experience with WDDX and XML-RPC, but as a foundation for HTML it was the best thing going. And maybe still is, given the absence of cross-toolchain contenders? Ditto for XSLT, at least if disregarding the choice to make the syntax homoiconic. In fact I circled back to XSLT long after it was clear it was a dead end. A good tool is a good tool, and the fact it remains so despite the wanton neglect only proves it.
> Well an XHTML parser (and serializer) is a lot simpler
Perhaps, but a combined html and xhtml parser is more complex than just a html parser. Since html already is entrenched, xhtml would be in addition to html, not instead of.
XML/XHTML is a fairly strict language syntax wise compared to HTML, tags are either explicitly self-closing i.e. <img/> or terminated with a matching closing-tag, no exceptions.
HTML has special rules depending on the tag's type, ie a bunch of them are just written (<img>) and the parser doesn't even really want to see a matching closing tag, or tags like <script> that has a special mode that stops being a HTML parser up until </script> is found. (1)
A HTML parser can become a XML parser by disabling a bunch of special-features and supporting self-closing tags (depending on XML level).
A XML parser needs a ton of "hacks" to become a HTML parser.
Also browsers needs an XML parser anyhow to support svg that's an xml-based format, also the DOM spec is written to support namespaces's like XML.
XSLT did complicate things, and most importantly it seems many relied on that one old implementation written in the 90s that was a swiss-cheese when it came to security concerns that nobody wanted to spend money on maintaining.
With the benefit of hindsight, if the web had been that way from the beginning, I think we would have been better off. The moment you tested your content in any browser, you'd immediately see if it was broken.
But it wasn't something that could get introduced later, after all the broken content that already existed.
With all respect - the opposite is true. The web succeeded because HTML and HTTP are easy standards easily writable by humans with text editors. HTML was writable by non-programmers.
Forgiving is very helpful in enticing those whose content you'd like to parse to start producing content. There's no use in having the worlds greatest pipeline if nothing is being put in and moved through. See the tragedy of the death of flash and "surely someone will come along and make a great frictionless editor for canvas and webgl", only for all the creative energy ending up being sucked up and monetised by roblox, leaving the world worse off.
Until html5 it wasn't forgiving - it was ambiguous. Different browsers could (and did) interpret different malformed html in different ways.
Once there was a standardized interpretation for malformed html, there was a chance that we could have treated that as a transparent conversion layer to xhtml. That isn't how WHATWG went, however.
I see what you are saying, but I don't think catering to sloppy growth over correctness needs to happen at the document level. The unrigorous shouldn't be given access at this level, you can still make php and myspace at other layers and using other abstractions. I think sloppy growth has its place, but it also needs the right level.
That's not obviously so. The adoption of JS wasn't particularly hindered by the fact that users have to match their brackets and generally avoid syntax errors.
i think xhtml happened before the wider world of web devs were ready for it. Component based architectures took longer to be adopted than I certainly expected.
It might actually work if reintroduced these days as long as we can consider many components to be valid documents.
Yeah, XSLT 1.0 has some really obvious missteps, so much so that to my knowledge basically nobody just implements XSLT 1.0. What they actually support is (most of) XSLT 1.0 plus a handful of EXSLT extensions (which are completely unofficial and not part of any XSLT spec, by the way). In my opinion the EXSLT stuff is the bare minimum needed to make XSLT 1.0 at least a passable language. Meanwhile, the XSLT spec evolved into 2.0 and 3.0, which as far as I'm aware, even to this day, has no complete open-source implementation.
Feels crazy to me that to date, this was the only widely supported way to pull in shared bits of HTML like headers, navigation, and footers without anything dynamic on either end. It’s such a basic and common use case to be so poorly covered.
Chrome is putting a big red button on any site using XSLT.
I'm for my RSS feed. It's ugly, I will have to move to another solution. It works fine on Firefox.
Good riddance. XSLT and EJB marked the dark ages of software development. For a half decade nothing made sense and programmers and management were going along with the charade until everyone collectively realized it was complete garbage and just stopped using it. I remember replacing an XSLT/EJB system that processed one order per minute with a C++ system written in a week that processed 10,000/minute. A team of a dozen programmers had been working on that XSLT disaster for years.
In retrospect I really think it was a deliberate plan by IBM and Sun to turn software development into such an awful, impenetrable quagmire that they would be the only ones who could build and maintain any system.
I encode all the text, localization, provenance, pedagogical, and forced alignment data for my Latin language audiobook chapters[0] as TEI-XML. When I fetch a document out BaseX, I have an XQM module that wraps the document in a number of XML processing instructions (PIs), one being a pointer to the reader XSLT 1.0 stylesheet which does all the HTML rendering client-side.
It's a cool system, and I'll be bummed when I have to do this on the server. I already get warnings in the Firefox console about them soon deprecating XSLT support, so it's not just Chrome.
I'd consider getting your workflow running in wasm (in wasmtime on the server) and then you can migrate the same workflow to the client using the same wasm module. Nearly all LLVM based compilers can compile to wasm (WebAssembly).
i just got flashbacks to a past life where i handcrafted XSLT to pre-render output from a service as HTML server side. Of course the front end was running some asp.net version and Microsoft flavored XSLT had lots of quirks.
More than ten years ago a coworker wrote a tool to generate Swift from iOS storyboards, to pass data through segues and give us typed access to identifiers. First version of it used XSLT to transform the storyboard XML. A powerful, if niche technology.
In the age of LLMs I would expect that legacy code bet carried indefinitely. The LLMs will have it indefinitely in their training data, and with code "cheap" to produce now, what are the good reasons for dropping legacy code?
Your presumption is that code is "cheap" because of LLMs. I am challenging the premise. Maintaining code in production for a product used by billions of people is not cheap, with or without LLMs. Perhaps your shitty disposable code that you write for yourself and never subject anyone else to is cheap, but if your code is in a large, complex codebase and has to actually work for everyone who uses it, not so much.
LLMs are only getting better and more competent, especially for code well-covered by tests. On such codebases it's definitely cheaper to maintain code with a LLM than by humans alone. I presume then that the XSLT implementation in Chrome is not well-tested.
Browsers have been relying on libxml2 for ages. Nobody bothered to help libxml2 much, let alone pay for maintenance, but treated it like a security critical component so let their CVE teams loose on unsuspecting volunteers. libxml2 burned out, the project got abandoned, and now Google and everyone else are sweating about what to do with their XML parsing code.
Ripping out the least common and most dangerous parts of XML parsing makes a lot of sense if you want to keep using the unmaintained library without actually having to put in the work to maintain it.
The libxml2 maintainer forked the repo and released it as AGPL, a license which does to Google what garlic does to vampires, unless you pay up.
XSLT is rarely used, a significant attack surface, and the upstream libraries are riddled with vulnerabilities. LLMs make the problem worse by lowering the cost of finding new vulnerabilities.
The breakage that sticks out to me is that IIS in Windows Server outputs some reports as XML+XSLT and these have become nigh unusable for years now.
I ignore every official statement about “support” and simply look at the horse's mouth: Microsoft hasn’t bothered to fix this in IIS, and likely never will.
It’s a dead product, “supported” only in a contractual sense, not a practical one.
(If you called support right now demanding fix for this, they’d tell you that it’s broken by design, have you tried moving to a recurring revenue service offering?)
It is wild to look back at XHTML and see that the W3C were entirely correct about XML. They envisaged a world of schemas, client side templating, custom elements, dynamic forms, the works.
Alas, for laughably bad reasons we had to scrap all that for HTML5, Javascript and CSS; a stack so awful that most devs doing anything on the frontend immediately scramble to React, TypeScript, Tailwind, whatever it takes to avoid the underlying garbage.
A horrid state of affairs that will only get worse as time goes on.
The XHTML/XML/XSLT tooling was bad, and XSLT was hard to reason about. That meant that amateurs had no way to learn it, and those amateurs went to school and became the workforce.
The web became a winner because it was easy to get something working. And then Google made it a mission to make great developer tools in everyone's hands for free.
I think in 2026 we could build the tooling around a better experience, but it would require thinking about the developer experience first.
You could do some awesome things with XML/XSL. My favorite was RSS feeds or OPML collections of RSS feeds (both flavors of XML) calling an XSL transformation when viewed in a web browser instead of mined by computers for data; same with TEI files, although that was a bit more arcane. The idea was that you'd have one data file for machine use and a way to present that data to humans as a web page.
But, as a stack, the XML/XSL/XPath/etc combination was weak because XSLT was hard to comprehend and never updated. No browser supports XSLT 2 or 3; they froze support with 1. XSLT 2 was 2007, a year before HTML 5 was a thing, yet it never got picked up by browsers. Javascript was just easier to understand than XSLT. Development of XHTML was also glacial, and people wanted new tags, especially for video.
> XSLT 2 was 2007, a year before HTML 5 was a thing, yet it never got picked up by browsers. Javascript was just easier to understand than XSLT.
Turns out that tasks easily done by programming languages are best done by programming languages. Who knew?
JSON allowing frontends and backends to communicate in a way analogous to the "smart endpoints, dumb pipes" model for networking saved the Web. The XML adherents wanted the inverted model, which was always insanely difficult to reason about and led to entirely XML-specific security threats.
Is that really accurate? In a world where HTML5 never happened, how would XHTML/XSLT solve the same problems that modern front-end Javascript frameworks do (interactive data-driven websites)? I say this as someone who thinks XSLT is a really useful technology, and doesn't want it to be deprecated.
That browser world would of been glorious without HTML5. Where Javascript wasn't in the browser and Tcl was (it was a contender); we would be working with plugin based browsers rather than built-in to the hood. That in turn would enable you to process incoming documents based in XSLT however you desired.
It would of been glorious having any programming language usable within the browser. Craft your own features rather than what's given to you now. It's only now that we're gaining the ability to use other languages via WASM.
Tcl was a contender to Javascript in the browser but Javascript won because it didn't require a plugin. And as Tcl never became the browser's default scripting environment juxtaposition Flash eventually lost because the browser platform evolved to make its proprietary plug-in unnecessary
I can't help but agree, and sometimes I think about the alternate version of the web where XML realized its full potential as the dominant technology. The obvious problem with XML is that the syntax is so verbose and redundant that it's only barely human-writable, but this is 100% a solvable problem.
The article says as much in the opening. It also includes a statement from Microsoft noting they do not intend to carry this forward separately, with a salient comment in one of the Microsoft page citations:
> For functionality and compatibility reasons, Microsoft Edge adopts nearly all of the Chromium project's changes to the web platform. However, Microsoft retains full control of the Microsoft Edge browser and may defer or reject changes.
Removed features don't always follow the same timelines either (and not just because of a lag in syncing to upstream Chromium).
Bless the Internet Archive for basically hosting a second copy of the internet with sufficient bandwidth to serve whatever is currently down, while this single site didn't survive the traffic it got individually
I feel the same way about this that I do about removing Flash support: it's good that we're moving on to better things, but that doesn't help if there aren't better things to move on to.
What's the simple goto for making web based games that kids can mess around with? It was Flash, and now it's nothing. How do you set up an RSS feed to not just blast raw XML at the user? Soon it won't be XSLT any more, but I don't see a good replacement (even more annoying is the fact that browsers used to have features to handle RSS feeds by themselves, and XSLT was used to sidestep that problem, but now there's no more side to step).
Are any of these newer templating languages worth me switching?
Step 1: Gain browser monopoly
Step 2: Generate fake security scare
Step 3: Gaslight everyone that only way to mitigate is to get rid of it completely like Flash.
Step 3a (corollary): There isn't anyone available that can fix the bugs because we spent all resources on UI/UX experimentation
I wouldn't say poor. Adobe had its own creative-software empire to up-keep. Photoshop, Illustrator, After Effects, and its web-authoring products gave it enormous influence over creative professionals. Macromedia's Dreamweaver and Flash were serious competitors in web design and interactive media. Adobe needed the missing monopoly cards; Flash, Fireworks and Dreamweaver were them.
Flash was security ridden yes, Flash required a plugin, yes; I don't think supported AppleOS at the time. These could of all been solved but I would agree that to refactor the software would of been an expensive take.
Jobs + HTML5, WebGL, JS all had entered the ring and finished the blow.
I miss it. Growing up with the internet in 2003, 2010's was the end of the wild world web. 2020's was the era of walled gardens for which we now have LLM's for the theme park and we're now entering 2030 where the internet is on fire with creativity now wrung between Yes Ai and No Ai.
My first ever domain name, registered with my pocket money at the age of 13. Hopefully 2040 should bring world peace. One would hope.You're half right.
Yes, Jobs killed Flash. But he did it because Flash on mobile was a battery killer. And when the original iPhone came out (one of which I still have), battery technology wasn't as advanced as it is now.
Before I got my wife's hand-me-down iPhone, I had one of the few mobile phones that supported Flash. On the few occasions when I used the web browser, I lived in fear that I'd land on a web site that was using Flash because I knew it would tear through the phone's battery in less than 10 minutes.
Ever notice that the people on HN who pine for the good-ol'-days of Flash only remember games? Never the Flash ads and intrusive videos.
Jobs did the future a favor.
Audio however was a crapshoot for years, especially for games.
Even basic WebAudio took until 2015, and the final piece to match Flash being AudioWorklet was only first available in 2018(Chrome) and took until April _2021_ land in Safari.
So before 2021 you needed to either write your own abstractions to support multiple API's with different execution models with so-so capabilties to be somewhat on-par with what Flash provided or even for years resort to simpler solutions (ie just samples).
I lost any enthusiasm for XML after my experience with WDDX and XML-RPC, but as a foundation for HTML it was the best thing going. And maybe still is, given the absence of cross-toolchain contenders? Ditto for XSLT, at least if disregarding the choice to make the syntax homoiconic. In fact I circled back to XSLT long after it was clear it was a dead end. A good tool is a good tool, and the fact it remains so despite the wanton neglect only proves it.
https://www.w3.org/TR/xml/#sec-starttags
Yeah and then we could have called it xhtml5. Too bad that does not exist. Oh wait https://html.spec.whatwg.org/multipage/xhtml.html
> But the anti-XML sentiment was explicit and spiteful.
No, xhtml was just a bad idea creating tons of problems and solving none.
Well an XHTML parser (and serializer) is a lot simpler, which is a pretty meaningful problem to solve.
What problems does xhtml create?
Perhaps, but a combined html and xhtml parser is more complex than just a html parser. Since html already is entrenched, xhtml would be in addition to html, not instead of.
HTML has special rules depending on the tag's type, ie a bunch of them are just written (<img>) and the parser doesn't even really want to see a matching closing tag, or tags like <script> that has a special mode that stops being a HTML parser up until </script> is found. (1)
A HTML parser can become a XML parser by disabling a bunch of special-features and supporting self-closing tags (depending on XML level).
A XML parser needs a ton of "hacks" to become a HTML parser.
Also browsers needs an XML parser anyhow to support svg that's an xml-based format, also the DOM spec is written to support namespaces's like XML.
XSLT did complicate things, and most importantly it seems many relied on that one old implementation written in the 90s that was a swiss-cheese when it came to security concerns that nobody wanted to spend money on maintaining.
(1): https://html.spec.whatwg.org/multipage/parsing.html#script-d...
But it wasn't something that could get introduced later, after all the broken content that already existed.
But then, I've always preferred strongly typed over stringly typed.
The reason HTML and markdown are more widely adopted than latex is because the former are more forgiving.
Once there was a standardized interpretation for malformed html, there was a chance that we could have treated that as a transparent conversion layer to xhtml. That isn't how WHATWG went, however.
It might actually work if reintroduced these days as long as we can consider many components to be valid documents.
Sure there is some embedded JS in there as well but ignore that and JSX is thr XHTML comeback story.
Ex: https://ache.one/en/rss.xml
It's a cool system, and I'll be bummed when I have to do this on the server. I already get warnings in the Firefox console about them soon deprecating XSLT support, so it's not just Chrome.
[0]: https://fabulae.orbilii.com
I can't load this page.
Reducing attack surface.
Ripping out the least common and most dangerous parts of XML parsing makes a lot of sense if you want to keep using the unmaintained library without actually having to put in the work to maintain it.
The libxml2 maintainer forked the repo and released it as AGPL, a license which does to Google what garlic does to vampires, unless you pay up.
LLMs make the problem easier because lowering the cost of fixing the vulnerabilities
Use css to style them instead?
Removing XSLT for a more secure browser(https://developer.chrome.com/docs/web-platform/deprecating-x...) 183 points|justin-reeves|1 year ago|337 comments https://news.ycombinator.com/item?id=45823059
Intent to Deprecate and Remove XSLT(https://groups.google.com/a/chromium.org/g/blink-dev/c/CxL4g...) 87 points|CharlesW|1 year ago|149 comments https://news.ycombinator.com/item?id=45779261
A look at XSLT 3.0 (2017)(https://www.xml.com/articles/2017/02/14/why-you-should-be-us...) 75 points|protomolecool|1 year ago|45 comments https://news.ycombinator.com/item?id=45026013
Show HN: I Built a XSLT Blog Framework(https://vgr.land/content/posts/20250821.xml) 116 points|vgr-land|1 year ago|68 comments https://news.ycombinator.com/item?id=45006098
Show HN: JavaScript-free (X)HTML Includes(https://github.com/Evidlo/xsl-website) 211 points|Evidlo|1 year ago|114 comments https://news.ycombinator.com/item?id=44988271
Should the web platform adopt XSLT 3.0?(https://github.com/whatwg/html/issues/11578) 133 points|protomolecool|1 year ago|108 comments https://news.ycombinator.com/item?id=44987552
XSLT removal will break multiple government and regulatory sites(https://github.com/whatwg/html/issues/11582) 160 points|colejohnson66|1 year ago|146 comments https://news.ycombinator.com/item?id=44987346
Google did not unilaterally decide to kill XSLT(https://meyerweb.com/eric/thoughts/2025/08/22/no-google-did-...) 103 points|bkardell|1 year ago|128 comments https://news.ycombinator.com/item?id=44987239
"Remove mentions of XSLT from the html spec"(https://github.com/whatwg/html/pull/11563) 388 points|troupo|1 year ago|535 comments https://news.ycombinator.com/item?id=44952185
Should we remove XSLT from the web platform?(https://github.com/whatwg/html/issues/11523) 73 points|edent|1 year ago|96 comments https://news.ycombinator.com/item?id=44909599
XSLT: A Precision Tool for the Future of Structured Transformation(https://www.xml.com/articles/2025/07/19/xslt-precision-tool-...) 58 points|protomolecool|1 year ago|59 comments https://news.ycombinator.com/item?id=44633384
XSLT – Native, zero-config build system for the Web(https://github.com/pacocoursey/xslt) 392 points|_kush|1 year ago|325 comments https://news.ycombinator.com/item?id=44393817
Intent to Unship: XSLT(https://groups.google.com/a/mozilla.org/g/dev-platform/c/ZRy...) 5 points|tambourine_man|2 months ago|1 comments
(this list is incomplete. but we just had a power outage (including getting zapped, so i am submitting this now to not lose it)
I ignore every official statement about “support” and simply look at the horse's mouth: Microsoft hasn’t bothered to fix this in IIS, and likely never will.
It’s a dead product, “supported” only in a contractual sense, not a practical one.
(If you called support right now demanding fix for this, they’d tell you that it’s broken by design, have you tried moving to a recurring revenue service offering?)
Alas, for laughably bad reasons we had to scrap all that for HTML5, Javascript and CSS; a stack so awful that most devs doing anything on the frontend immediately scramble to React, TypeScript, Tailwind, whatever it takes to avoid the underlying garbage.
A horrid state of affairs that will only get worse as time goes on.
The XHTML/XML/XSLT tooling was bad, and XSLT was hard to reason about. That meant that amateurs had no way to learn it, and those amateurs went to school and became the workforce.
The web became a winner because it was easy to get something working. And then Google made it a mission to make great developer tools in everyone's hands for free.
I think in 2026 we could build the tooling around a better experience, but it would require thinking about the developer experience first.
But, as a stack, the XML/XSL/XPath/etc combination was weak because XSLT was hard to comprehend and never updated. No browser supports XSLT 2 or 3; they froze support with 1. XSLT 2 was 2007, a year before HTML 5 was a thing, yet it never got picked up by browsers. Javascript was just easier to understand than XSLT. Development of XHTML was also glacial, and people wanted new tags, especially for video.
Turns out that tasks easily done by programming languages are best done by programming languages. Who knew?
JSON allowing frontends and backends to communicate in a way analogous to the "smart endpoints, dumb pipes" model for networking saved the Web. The XML adherents wanted the inverted model, which was always insanely difficult to reason about and led to entirely XML-specific security threats.
It would of been glorious having any programming language usable within the browser. Craft your own features rather than what's given to you now. It's only now that we're gaining the ability to use other languages via WASM.
Tcl was a contender to Javascript in the browser but Javascript won because it didn't require a plugin. And as Tcl never became the browser's default scripting environment juxtaposition Flash eventually lost because the browser platform evolved to make its proprietary plug-in unnecessary
> For functionality and compatibility reasons, Microsoft Edge adopts nearly all of the Chromium project's changes to the web platform. However, Microsoft retains full control of the Microsoft Edge browser and may defer or reject changes.
Removed features don't always follow the same timelines either (and not just because of a lag in syncing to upstream Chromium).