This is how the simplest variant of SGML (or XML) entities have worked since 1986:
<!doctype html [
<!entity e system "e.html">
]>
<html>
<title>Hello, world!</title>
<p>The content of e is: &e;</p>
</html>
HTML was envisioned as an SGML vocabulary from day one. That SGML's document composition and other facilities were used only at authoring time and not directly supported by browsers was merely due to the very early stage of the first browser software ([1]) which directly mentions SGML even, just as HTML specs have presented HTML as a language for authoring and not just delivery since at least version 4.
There really never had been a need or call for browser devs to come up with idiosyncratic and overcomplicated solutions relying on JavaScript for such a simple and uncontroversial facility as a text macro which was part of every document/markup language in existance since the 1960s.
Since this seems to be about the recent proposal to remove xslt, i'd point out you can do the same thing with CSS
https://bawolff.net/css-website/index.xml is Evidlo's example but using a css stylesheet instead of xslt. I changed some of the text to explain what i was doing, but otherwise the XML is unchanged with one exception. Unfortunately you do have to put the <a> tags in the xhtml namespace to make them clickable. Other than that no changes to the xml.
Obviously there is a lot that xslt can do that css cannot, but when it comes to just display, CSS is an option here.
This is really, definitely cool, but it's important to remember that content added via CSS is purely decorative. It can't be interacted with, which is a major issue for assistive technologies like screen readers.
Yeah, i saw. Unfortunately the advanced example wouldn't be doable in CSS. I suppose i'm being a bit intellectually dishonest to not explicitly point that out.
This latter part is why I've reached for XSLT in the past. Most recently was to convert an RSS feed into a styled page with instructions at the top. Templates and xpath can really transform a document.
To overcome the two problems here (client side loading the template and ending browser support) you could throw in php in the mix and have a wonderful solution for templating with bullet proof standards:
// XML
$xml_doc = new DOMDocument();
$xml_doc->load("file1.xml");
// XSL
$xsl_doc = new DOMDocument(); $xsl_doc->load("file.xsl");
// Proc
$proc = new XSLTProcessor();
$proc->importStylesheet($xsl_doc);
$newdom = $proc->transformToDoc($xml_doc);
I'm sorry, this a dumb comment that has no basis in reality.
HTML Imports was part of the initial set of the web components specs, there's no "cabal" or whatever that got its hands on it, and it didn't rely on JavaScript, not in the way you're probably referring to.
It was only opposed because it was separate from the JS module system, not because it relied on JS.
It's replacement: The HTML Modules proposal has general support from all vendors, just no one has put together a complete proposal yet.
Exactly. I think the problem wasn't that browsers (specifically Firefox and Safari) were opposed to the idea of html includes in general, but they didn't like the specific proposal, in large part because it still required javascript, and added a lot of complexity for little to no benefit.
I think rejecting that proposal was the right thing to do. What disappoints me is that there hasn't been a more declaritive, simpler proposal that has gotten anywhere.
> What disappoints me is that there hasn't been a more declaritive, simpler proposal that has gotten anywhere.
Possible names:
Client Side Includes (CSI): Like Server Side Includes (SSI) in Apache
IHTML (inline html): Like the iframe tag, but for html instead of whole page.
> As of the next version of Chrome, XSLT will be gated behind a flag.
Citation? That would greatly surprise me in its abruptness and severity (they only just started talking about it this month, and acknowledge it’s particularly risky for enterprise) and https://chromestatus.com/feature/4709671889534976 gives no such indication.
The meeting referenced there, from March not last month, also gives no indication that they'd go ahead and make any moves - "stick a pin in it". But they did anyway. [0]
panos: next item, removing XSLT. There are usage numbers.
stephen: I have concerns. I kept this up to date historically for Chromium, and I don't trust the use counters based on my experience. Total usage might be higher.
dan: even if the data were accurate, not enough zeros for the usage to be low enough.
mason: is XSLT supported officially?
simon: supported
mason: maybe we could just mark it deprecated in the spec, to make the statement that we're not actively working on it.
brian: we could do that on MDN too. This would be the first time we have something baseline widely available that we've marked as removed.
dan: maybe we could offer helpful pointers to alternatives that are better, and why they're better.
panos: maybe a question for olli. But I like brian's suggestion to mark it in all the places.
dan: it won't go far unless developers know what to use instead.
brian: talk about it in those terms also. Would anyone want to come on the podcast and talk about it? I'm guessing people will have objections.
emilio: we have a history of security bugs, etc.
stephen: yeah that was a big deal
mason: yeah we get bugs about it and have to basically ignore them, which sucks
brian: people do use it and some like it
panos: put a pin in it, and talk with olli next time?
panos: next thing is file upload control rendering
Did what? The GP asked for a citation for XSLT support going behind a flag in the next version of Chrome, but you forgot to add that. As best as I can tell, the GP is right and you're confused.
By “started talking about it this month” I meant this specific advocation for removing it. Yes, it’s been talked about for years, but this time it’s specific.
Again, that’s prior discussion. It’s happened a few times over the last few years.
Then another few months pass, and one of the agitators goes about formally proposing removing it, so that finally it isn’t just murmurings more or less behind closed doors, but out in public for the developers to clamour about. That’s where we are this month.
It's kind of too bad XSLT didn't take off. It is quite complex, until you compare it to the complexity of what now solves this problem (e.g. a build step with React and webpack and javascript absolutely required on the client-side). As the OP ably demonstrates, XSLT provides a declarative, non-javascript, non-build way to solve the basic HTML component problem. Perhaps a devastating 0-day in V8 will make us really, really want an alternative to the current best practice.
Whilst I can't be certain, I've been hearing that part of Google's want to move away from XSLT is two-fold - and relates to the idea of the security problem.
Partly, there's increasing attacks against XML.
And also, libxml2 has said "no" to security embargoes altogether. [0]
They might well consider there to be 0-days waiting in XSLT.
I think the big difference there is that browsers are only responsible for Javascript, which is a big general purpose solution that solves a lot of problems and not just templating/styling XML. Everything else either happens server-side (build steps and webpack) or is userland code that lives inside the sandbox. So there's one task for browsers to do (make a fast and secure Javascript sandbox), and if that works that developers can do whatever they want. Whereas XSLT is not a general purpose tool in the same way, and so needs to be maintained in addition to Javascript and anything else that exists.
If course XSLT can also be used server-side (which is probably a good idea if you want access to the latest features and not some ancient, frozen version of the spec), but browsers aren't the reason that that didn't take off. My guess there is that it's just not an intuitive way of manipulating and templating data in comparison to more traditional HTML templating libraries.
React supports rendering to HTML ahead of time (SSR) which doesn't need any client-side javascript, and this is a prominent feature of most frameworks using React. This feature of React was one of its major innovations over many other front-end frameworks of the time.
It doesn't seem weird at all to me: standard is essentially the consensus of the major browser vendors; a spec which all of Chrome, Safari and Edge don't implement is really just a hypothetical.
The origin story of whatwg is that Apple, Mozilla and Opera decided that W3C wasn't making specs that they wanted to implement, so they created a new working group to make them.
If I understand correctly, Mozilla and Apple don’t really want to support it either. And the reason for that is, the spec is still at XSLT 1.0, which is super old, and current implementations are effectively abandonware. Catch-22?
I believe the spec is at XSLT 3.0 but no browser actually implemented past XSLT 1.0 (not 100% sure - almost nobody cared about this feature last month so hard to find good docs on support). HTML5 and C++ are cut from the same cloth - massive and no reference implementation so full of features that have been “standard” for 10 years but never implemented by anyone.
Yeah, sorry, the XSLT spec is at 3.0 right now of course, but the browsers don’t implement it, and the WHATWG HTML Living Standard only mentions XSLT 1.0.
To be fair, some things should be legitimately considered to be removed from the standard. O.G. XHTML basically mandated that you accept XML logic bombs and we got over that.
Also, while this is certainly Google throwing their weight around, I don’t think they are doing it for monetary advantage. I’m not sure how removing XSLT burnishes their ad empire the way things like nerfing ManifestV3 have. I think their stated reasons - that libxslt is a security disaster zone for an obscure 90s-era feature - is earnest even if its not actually in the broader web’s best interests. Now that Safari is publicly on board to go second, I suspect it’s an inevitability.
XML "logic bombs" happens when the parser expand entities eagerly. If a parser does that one can easily assemble an enormous entity that will eat up all the memory. But a more sophisticated parser won't expand entities right away and thus can merely reject oversized ones. It is really a minor issue.
I’ve seen a lot of eye-batting about this. Although Google, Mozilla and Apple are all in favour of removing it, there’s been a lot of backlash from developers.
Most of whom had never heard of XSLT before today - some were likely born after it had faded into obscurity. I don’t blame people for hating Google for whatever reason, but this is a weird way to try to stick it to them.
A small comment for anyone new to xslt. The author references a wildcard rule in the comments [0]. While that is true, they are calling an identity transformation [1]. Identity transformations are very common in xslt.
I used to do this in the 2000's era, there was a lot to love about it.
At the time though the IE engines were far more complete and less buggy than others with various XML features.
This looks like as good a place as any to show the XML/XSLT code that I've been tinkering with for the last couple of years: https://github.com/zmodemorg/wyrm.org
This works client side right? So when a user navigates to this page, it recursively fetches content from the server? And if you have nested includes it would waterfall?
Even single page app frameworks have mostly solved this by doing the rendering on the server instead of making multiple round trips from the client. This feels like the no-JavaScript version of Spinnergeddon.
Does the browser wait for all the includes to resolve before showing the page or does it flicker in?
If you want server-side compilation, you could just run the xslt transform in ci/cd. It would still be a simpler solution than Jekyll in some regards, but I probably wouldn't do it for more than hobby projects
Looking at the xslt stylesheet , it doesn't look like there are nested includes, its just one stylesheet which doesn't include anything else. So its not that different in terms of requests than how css would work.
It's making three round trips. The first is to get the original xml file, then it's to load the second xml file, then it's to load the stylesheet.
Now you can imagine with a real site, you will have many includes per page, each one perhaps using includes of it's own. You end up with a really bad waterfall where it can take a long time for a page to load because it's going back to the server constantly, whereas if you did it on the server it would be a single round trip.
Early SPA's did this, they would load a shell and then begin fetching from the client. Some still do but we know better than to do this for things that aren't web apps.
> You end up with a really bad waterfall where it can take a long time for a page to load because it's going back to the server constantly, whereas if you did it on the server it would be a single round trip.
These are all static file downloads, though. The first page load will take long, but if these are header/footer type includes, every subsequent page will use the cached file.
It's a trade-off between longer times for landing page and shorter times for every other page. The developer will decide whether or not to make the trade-off.
The stylistic includes and certain content (e. g. a site map) can be embedded in the XSLT itself.
It is not quite a templating engine. XSLT is a part of a semantic engine. Content is written in the way that fits the content. E. g. I write about some language and invent tags and notations that best fit what I am talking about: grammar, sounds, wrtiting. Or I write about chess and say something like (party id=abc move=15w). Then I make it available in HTML by providing a transform from my tags to HTML tags. My notation is rendered as a bunch of divs, ps and spans. This is merely a temporary rendering; other renderings may be possible.
A templating engine is the final document with placeholders for variable parts. XSLT can do that too, but this is less than its vision.
The most advanced usage of XSLT I've seen was in YBlog2, YML and YSLT, an alternative syntax for XML and XSLT. And IIUC they did not rely on browser-side although that may be still possible.
Three jobs ago I worked for a company that did e-learning systems for industrial clients. This was roughly 2004. One of the company owner's many ideas was a technical documentation system based on XML and XSLT. The "idea" being that technical writers or SMEs would rather write XML than, you know, use a word processor.
Unsurprisingly the idea did not take off, but I did find the XML/XSLT combination to be very interesting.
This is how the simplest variant of SGML (or XML) entities have worked since 1986:
HTML was envisioned as an SGML vocabulary from day one. That SGML's document composition and other facilities were used only at authoring time and not directly supported by browsers was merely due to the very early stage of the first browser software ([1]) which directly mentions SGML even, just as HTML specs have presented HTML as a language for authoring and not just delivery since at least version 4.There really never had been a need or call for browser devs to come up with idiosyncratic and overcomplicated solutions relying on JavaScript for such a simple and uncontroversial facility as a text macro which was part of every document/markup language in existance since the 1960s.
[1]: https://info.cern.ch/hypertext/WWW/MarkUp/MarkUp.html
Since this seems to be about the recent proposal to remove xslt, i'd point out you can do the same thing with CSS
https://bawolff.net/css-website/index.xml is Evidlo's example but using a css stylesheet instead of xslt. I changed some of the text to explain what i was doing, but otherwise the XML is unchanged with one exception. Unfortunately you do have to put the <a> tags in the xhtml namespace to make them clickable. Other than that no changes to the xml.
Obviously there is a lot that xslt can do that css cannot, but when it comes to just display, CSS is an option here.
This is really, definitely cool, but it's important to remember that content added via CSS is purely decorative. It can't be interacted with, which is a major issue for assistive technologies like screen readers.
Thanks for the CSS example.
By the way, the advanced/ folder has a slightly more complicated example that demonstrates template inheritance and "slots".
Yeah, i saw. Unfortunately the advanced example wouldn't be doable in CSS. I suppose i'm being a bit intellectually dishonest to not explicitly point that out.
> there is a lot that xslt can do that css cannot
This latter part is why I've reached for XSLT in the past. Most recently was to convert an RSS feed into a styled page with instructions at the top. Templates and xpath can really transform a document.
Umm..your CSS example doesn't show any template includes. No way to put header/footer in separate files.
The original example didn't have that either.
> i'd point out you can do the same thing with CSS
Cool when are they removing CSS from the standard?
To overcome the two problems here (client side loading the template and ending browser support) you could throw in php in the mix and have a wonderful solution for templating with bullet proof standards: // XML $xml_doc = new DOMDocument(); $xml_doc->load("file1.xml");
// XSL $xsl_doc = new DOMDocument(); $xsl_doc->load("file.xsl");
// Proc $proc = new XSLTProcessor(); $proc->importStylesheet($xsl_doc); $newdom = $proc->transformToDoc($xml_doc);
// Output print $newdom->saveXML();
XSLT lacks functionality? No problem, use php functions in xslt: https://www.php.net/manual/en/class.xsltprocessor.php
Why didn't HTML imports stick around? https://web.dev/articles/imports
The moronic Web Component cabal got their hands on it and trashed it by forcing it to rely on JavaScript, thus ensuring it would never get support.
I'm sorry, this a dumb comment that has no basis in reality.
HTML Imports was part of the initial set of the web components specs, there's no "cabal" or whatever that got its hands on it, and it didn't rely on JavaScript, not in the way you're probably referring to.
It was only opposed because it was separate from the JS module system, not because it relied on JS.
It's replacement: The HTML Modules proposal has general support from all vendors, just no one has put together a complete proposal yet.
For a long time web components generally built on four standards:
https://korban.net/posts/elm/2018-09-17-introduction-custom-...Eventually it became clear some browsers were not going to implement and the design of HTML imports was better handled be ES modules.
https://webmasters.stackexchange.com/questions/127482/on-wha...
Found this, it should answer your complaints:
> HTML Imports were redundant, since you need JavaScript to bring them alive anyways
Exactly. I think the problem wasn't that browsers (specifically Firefox and Safari) were opposed to the idea of html includes in general, but they didn't like the specific proposal, in large part because it still required javascript, and added a lot of complexity for little to no benefit.
I think rejecting that proposal was the right thing to do. What disappoints me is that there hasn't been a more declaritive, simpler proposal that has gotten anywhere.
HTML Imports and HTML includes are two different ideas. HTML Imports was never like what people want from HTML includes.
HTML Imports were shelved because they didn't integrate with the JS module graph. HTML Modules will do that someday.
> What disappoints me is that there hasn't been a more declaritive, simpler proposal that has gotten anywhere.
Possible names: Client Side Includes (CSI): Like Server Side Includes (SSI) in Apache IHTML (inline html): Like the iframe tag, but for html instead of whole page.
As of the next version of Chrome, XSLT will be gated behind a flag.
Google have also asked for it to be removed from the standard [0].
[0] https://github.com/WHATWG/html/issues/11523
> As of the next version of Chrome, XSLT will be gated behind a flag.
Citation? That would greatly surprise me in its abruptness and severity (they only just started talking about it this month, and acknowledge it’s particularly risky for enterprise) and https://chromestatus.com/feature/4709671889534976 gives no such indication.
The meeting referenced there, from March not last month, also gives no indication that they'd go ahead and make any moves - "stick a pin in it". But they did anyway. [0]
panos: next item, removing XSLT. There are usage numbers.
stephen: I have concerns. I kept this up to date historically for Chromium, and I don't trust the use counters based on my experience. Total usage might be higher.
dan: even if the data were accurate, not enough zeros for the usage to be low enough.
mason: is XSLT supported officially?
simon: supported
mason: maybe we could just mark it deprecated in the spec, to make the statement that we're not actively working on it.
brian: we could do that on MDN too. This would be the first time we have something baseline widely available that we've marked as removed.
dan: maybe we could offer helpful pointers to alternatives that are better, and why they're better.
panos: maybe a question for olli. But I like brian's suggestion to mark it in all the places.
dan: it won't go far unless developers know what to use instead.
brian: talk about it in those terms also. Would anyone want to come on the podcast and talk about it? I'm guessing people will have objections.
emilio: we have a history of security bugs, etc.
stephen: yeah that was a big deal
mason: yeah we get bugs about it and have to basically ignore them, which sucks
brian: people do use it and some like it
panos: put a pin in it, and talk with olli next time?
panos: next thing is file upload control rendering
[0] https://github.com/whatwg/html/issues/11146#issuecomment-275...
> But they did anyway.
Did what? The GP asked for a citation for XSLT support going behind a flag in the next version of Chrome, but you forgot to add that. As best as I can tell, the GP is right and you're confused.
By “started talking about it this month” I meant this specific advocation for removing it. Yes, it’s been talked about for years, but this time it’s specific.
> brian: we could do that on MDN too. This would be the first time we have something baseline widely available that we've marked as removed.
They were advocating for removing it. And it was specific. And is labelled by the Chromium report you mentioned as the cause.
It wasn't "this month".
Again, that’s prior discussion. It’s happened a few times over the last few years.
Then another few months pass, and one of the agitators goes about formally proposing removing it, so that finally it isn’t just murmurings more or less behind closed doors, but out in public for the developers to clamour about. That’s where we are this month.
It's kind of too bad XSLT didn't take off. It is quite complex, until you compare it to the complexity of what now solves this problem (e.g. a build step with React and webpack and javascript absolutely required on the client-side). As the OP ably demonstrates, XSLT provides a declarative, non-javascript, non-build way to solve the basic HTML component problem. Perhaps a devastating 0-day in V8 will make us really, really want an alternative to the current best practice.
Whilst I can't be certain, I've been hearing that part of Google's want to move away from XSLT is two-fold - and relates to the idea of the security problem.
Partly, there's increasing attacks against XML.
And also, libxml2 has said "no" to security embargoes altogether. [0]
They might well consider there to be 0-days waiting in XSLT.
[0] https://news.ycombinator.com/item?id=44381093
I think the big difference there is that browsers are only responsible for Javascript, which is a big general purpose solution that solves a lot of problems and not just templating/styling XML. Everything else either happens server-side (build steps and webpack) or is userland code that lives inside the sandbox. So there's one task for browsers to do (make a fast and secure Javascript sandbox), and if that works that developers can do whatever they want. Whereas XSLT is not a general purpose tool in the same way, and so needs to be maintained in addition to Javascript and anything else that exists.
If course XSLT can also be used server-side (which is probably a good idea if you want access to the latest features and not some ancient, frozen version of the spec), but browsers aren't the reason that that didn't take off. My guess there is that it's just not an intuitive way of manipulating and templating data in comparison to more traditional HTML templating libraries.
React supports rendering to HTML ahead of time (SSR) which doesn't need any client-side javascript, and this is a prominent feature of most frameworks using React. This feature of React was one of its major innovations over many other front-end frameworks of the time.
> React supports rendering to HTML ahead of time (SSR)...
So does XSLT?
I don't think react is comparable.
React's main thinh is client side reactivity, something that xslt doesn't offer.
A closer comparison would be a templating engine that does statuc conversion to html.
Yeah, I think that was what prompted this submission.
All this has also reignited my idea for a compile-to-XSLT templating language, too – maybe I’ll get to it finally this time; definitely if XSLT 3.0 gets into web standards: https://github.com/whatwg/html/issues/11578, https://news.ycombinator.com/item?id=44987552
Also, I’ve put together a simple XSLT playgroung a while ago! https://xsltbin.ale.sh/
I was thinking it would be possible to compile a subset of Jinja2 (or your favorite equivalent) into XSL: https://chatgpt.com/share/68a95439-ad54-800a-919f-23caecce43...
Thanks for the playground! I'll check it out.
I find it bizarre that Google can just ask for a feature to be removed from standard and nobody bats an eye.
It doesn't seem weird at all to me: standard is essentially the consensus of the major browser vendors; a spec which all of Chrome, Safari and Edge don't implement is really just a hypothetical.
The origin story of whatwg is that Apple, Mozilla and Opera decided that W3C wasn't making specs that they wanted to implement, so they created a new working group to make them.
If I understand correctly, Mozilla and Apple don’t really want to support it either. And the reason for that is, the spec is still at XSLT 1.0, which is super old, and current implementations are effectively abandonware. Catch-22?
I believe the spec is at XSLT 3.0 but no browser actually implemented past XSLT 1.0 (not 100% sure - almost nobody cared about this feature last month so hard to find good docs on support). HTML5 and C++ are cut from the same cloth - massive and no reference implementation so full of features that have been “standard” for 10 years but never implemented by anyone.
Yeah, sorry, the XSLT spec is at 3.0 right now of course, but the browsers don’t implement it, and the WHATWG HTML Living Standard only mentions XSLT 1.0.
even outside of browsers barely anything supports XSLT newer than 1.0
The spec is at XLST 3 right now.
Browsers only implement XSLT 1
https://meyerweb.com/eric/thoughts/2025/08/22/no-google-did-...
We were talking about the spec, not the implementation.
To be fair, some things should be legitimately considered to be removed from the standard. O.G. XHTML basically mandated that you accept XML logic bombs and we got over that.
Also, while this is certainly Google throwing their weight around, I don’t think they are doing it for monetary advantage. I’m not sure how removing XSLT burnishes their ad empire the way things like nerfing ManifestV3 have. I think their stated reasons - that libxslt is a security disaster zone for an obscure 90s-era feature - is earnest even if its not actually in the broader web’s best interests. Now that Safari is publicly on board to go second, I suspect it’s an inevitability.
XML "logic bombs" happens when the parser expand entities eagerly. If a parser does that one can easily assemble an enormous entity that will eat up all the memory. But a more sophisticated parser won't expand entities right away and thus can merely reject oversized ones. It is really a minor issue.
> nobody bats an eye
I’ve seen a lot of eye-batting about this. Although Google, Mozilla and Apple are all in favour of removing it, there’s been a lot of backlash from developers.
Most of whom had never heard of XSLT before today - some were likely born after it had faded into obscurity. I don’t blame people for hating Google for whatever reason, but this is a weird way to try to stick it to them.
Even "champion of the web" Mozilla is on board. Tells you exactly what you need to know.
so it's time to use XSLT more
A small comment for anyone new to xslt. The author references a wildcard rule in the comments [0]. While that is true, they are calling an identity transformation [1]. Identity transformations are very common in xslt.
[0] https://github.com/Evidlo/xsl-website/blob/0dda1d82ce1eb01b7... [1] https://en.wikipedia.org/wiki/Identity_transform
I used to do this in the 2000's era, there was a lot to love about it. At the time though the IE engines were far more complete and less buggy than others with various XML features.
Looks promising!
This looks like as good a place as any to show the XML/XSLT code that I've been tinkering with for the last couple of years: https://github.com/zmodemorg/wyrm.org
This works client side right? So when a user navigates to this page, it recursively fetches content from the server? And if you have nested includes it would waterfall?
Even single page app frameworks have mostly solved this by doing the rendering on the server instead of making multiple round trips from the client. This feels like the no-JavaScript version of Spinnergeddon.
Does the browser wait for all the includes to resolve before showing the page or does it flicker in?
If you want server-side compilation, you could just run the xslt transform in ci/cd. It would still be a simpler solution than Jekyll in some regards, but I probably wouldn't do it for more than hobby projects
Looking at the xslt stylesheet , it doesn't look like there are nested includes, its just one stylesheet which doesn't include anything else. So its not that different in terms of requests than how css would work.
> Looking at the xslt stylesheet , it doesn't look like there are nested includes, its just one stylesheet which doesn't include anything else
At least the browser has to load template.xsl before it can know it has to load the css file though, right? And this is just a simple demo page.
I guess its ine extra layer, but its not like we've gone 14 layers deep or something.
I imagine preloading the css file using the http link header would solve this problem.
It's making three round trips. The first is to get the original xml file, then it's to load the second xml file, then it's to load the stylesheet.
Now you can imagine with a real site, you will have many includes per page, each one perhaps using includes of it's own. You end up with a really bad waterfall where it can take a long time for a page to load because it's going back to the server constantly, whereas if you did it on the server it would be a single round trip.
Early SPA's did this, they would load a shell and then begin fetching from the client. Some still do but we know better than to do this for things that aren't web apps.
> You end up with a really bad waterfall where it can take a long time for a page to load because it's going back to the server constantly, whereas if you did it on the server it would be a single round trip.
These are all static file downloads, though. The first page load will take long, but if these are header/footer type includes, every subsequent page will use the cached file.
It's a trade-off between longer times for landing page and shorter times for every other page. The developer will decide whether or not to make the trade-off.
The stylistic includes and certain content (e. g. a site map) can be embedded in the XSLT itself.
It is not quite a templating engine. XSLT is a part of a semantic engine. Content is written in the way that fits the content. E. g. I write about some language and invent tags and notations that best fit what I am talking about: grammar, sounds, wrtiting. Or I write about chess and say something like (party id=abc move=15w). Then I make it available in HTML by providing a transform from my tags to HTML tags. My notation is rendered as a bunch of divs, ps and spans. This is merely a temporary rendering; other renderings may be possible.
A templating engine is the final document with placeholders for variable parts. XSLT can do that too, but this is less than its vision.
The most advanced usage of XSLT I've seen was in YBlog2, YML and YSLT, an alternative syntax for XML and XSLT. And IIUC they did not rely on browser-side although that may be still possible.
Three jobs ago I worked for a company that did e-learning systems for industrial clients. This was roughly 2004. One of the company owner's many ideas was a technical documentation system based on XML and XSLT. The "idea" being that technical writers or SMEs would rather write XML than, you know, use a word processor.
Unsurprisingly the idea did not take off, but I did find the XML/XSLT combination to be very interesting.