XSLT 2+ was more about side effects.
I never really grokked later XSLT and XPath standards though.
XSLT 1.0 had a steep learning curve, but it was elegant in a way poetry is elegant because of extra restrictions imposed on it compared to prose. You really had to stretch your mind to do useful stuff with it. Anyone remembers Muenchian grouping? It was gorgeous.
Newer standards lost elegance and kept the ugly syntax.
No wonder they lost mindshare.
My biggest problem with XSLT is that I've never encountered a problem that I wouldn't rather solve with an XPath library and literally any other general purpose programming language.
When XSLT was the only thing with XPath you could rely on, maybe it had an edge, but once everyone has an XPath library what's left is a very quirky and restrictive language that I really don't like. And I speak Haskell, so the critic reaching for the reply button can take a pass on the "Oh you must not like functional programming" routine... no, Haskell is included in that set of "literally any other general purpose programming language" above.
There's clearly value in XSLT's near-universal support as a web-native system. It provides templating out of the box without invoking JavaScript, and there's demand for that[1]. But it still lacks decent in-browser debugging which JS has in spades.
[1] https://justinfagnani.com/2025/06/26/the-time-is-right-for-a...
XML world is full of ugly standards and failed contenders. None remembers RelaxNG. But had reacher expressive power than XMLSchema and a human-readable syntax.
https://github.com/Juniper/libslax/wiki/Intro
It looks like it was developed by Juniper and has shipped in their routers?
Just to frame this people, imagine a JSON-based programming language for transforming JSON files into other JSON files and the program is also in JSON and turing complete. Now imagine it's not JSON but XML! Now any program can read it! Universal code, magic!
The idea behind XXSLT is now, we actually have a program whose job it is to specify a program. So we have a XML file which specifies a second XML file, which is the program, whose job it is to transform XML to XML. As we all know, layers of abstraction are always good, and common formats such as XML are especially good, so what we have now is the ability to generate a whole family and diverse ontology of programs, all of them XML, all of them by and for XML. Imagine the compiling with your favourite XML-based compilation chain!
XML (the data structure) needs a non-XML serialization.
Similar to how Semantic Web's Owl has four different serializations, only one of them being the XML serialization. (eg. Owl can be represented in Functional, Turtle, Manchester, Json, and N-triples syntaxes.)
That's YAML, and it is arguibly worse. Here's a sample YAML 1.2 document straight from their spec:
%TAG !e! tag:example.com,2000:app/
---
- !local foo
- !!str bar
- !e!tag%21 baz
--
Some notes:
- SemWeb also has JSON-LD serialization. It's a good compromise that fits modern tooling nicely.
- XML is still a damn good compromise between human readable and machine readable. Not perfect, but what is perfect anyway?
- HTML5 is now more complex than XHTML ever was (all sorts of historical caveats in this claim, I know, don't worry).
- Markup beauty is relative, we should accept that.
KDL is a very interesting attempt, but my impression is that people are already trying to shove way too much unnecessary complexity into it.
IMO, the KDL's document transformation is not a really good example of a better XSLT, tough. I mean, it's better, but it probably can still be improved a lot.
But the fundamental problem here is the same: no matter what new things are added to the spec, the best you can hope for in browsers is XSLT 1.0, even though we've had XSLT 3.0 for 8 years now.
Trying to close the gap often ends up creating more complexity than intended, or maybe even more than XML in some hands.
It definitely would be an interesting piece.
- Xee: https://github.com/Paligo/xee
- xrust: https://docs.rs/xrust/latest/xrust/xslt/
- XJSLT (compiles XSLT to JS): https://github.com/egh/xjslt
Xee is WIP AFAIK and I don't know the maturity of xrust and XJSLT.
Also, I want a cookie & a pony.