The thing most people never got about XSLT is that it is really about production rules -- and production rules (e.g. the major path to "expert systems") are one of the most solidly rejected technologies in software engineering.

I didn't understand this until I spent a few years going down a rabbit hole asking questions like "why don't people like production rules?" In the case of templating people expect to make a template with a top-down organization that looks like the output, whereas XSLT really wants you build transformations from the bottom-up. On some level the bottom-up part is clear, particularly if you want to code-generate your rules (towards the end I was writing production rules that write production rules) but what is not clear is how the parts all fit together: you can't visually tell between an XSLT that builds the structure you want vs one that doesn't.

I think the most fun I ever had with XSLT was when I used an XSLT engine with user-defined procedures and had them create side effects, such as matching certain patterns in an XML document and making SQL inserts, though that was a long time ago when we were still using terrible XML parsing libraries.

XSLT is not bad, but XML, unfortunately, is normally misused, so XSLT is tainted as it has to be a part of that misuse.

The true role of XML are grammar-based notations. These occur in two places: when a human gives data to a machine and when a machine produces data for a human. This is where XML is used despite its often mentioned shortcomings; for example, many notations to describe the user interface are based on XML. This is convenient, because user interfaces are created manually. (I am not mentioning text markup, it is well known.)

Yet XML was often used as a notation for machine-to-machine exchange. For example, the ONIX book description standard. Here data are moved between two computers, yet for some reason they have to form grammatically correct phrases according to a set of grammar rules. Computers do not need grammar. They do just fine with non-grammatical data, like a set of tables. It is way simpler for them; parsing or generating grammar, even explicit, is pure overhead for data exchange and is only necessary when data enters or leaves the computed pipeline.

So, to your examples: configuration in XML is actually fine, but IPC is not. Configuration is written by hand, IPC happens between machines. IPC specification, on the other hand, is also a good fit for XML.

That said, XML and thus XSLT has another flaw: it is way too verbose and has no good way to format it. Conciseness was an explicit no-goal but now we can say it was a mistake.

here on HN I dare to out myself as a DSSSL lover, the scheme based predecessor of xslt.

I still can't wrap my head around how the neat and clean dsssl syntax, a real programming language, was replaced by an xml notation for the same: for cuntional code and a framework. because semantically, that's what xslt is: a functional language with a framework, geared at transforming xml instances.

but that syntax... and of course a much inferior and more obscure language than scheme underneath dsssl.

I’m a big fan of XHTML (strictness is good) and feel like XSLT could be a great addition, but I hate the syntax. I’d love to build a Jinja to XSLT compiler one day.

I also have a simple playground for XSLT: https://xsltbin.ale.sh/

It's been a long number of years, but XUL (Mozilla/Firefox's UI layer) combined with XSLT was an incredible stack to build entire applications.

I regularly work with APIs in shell that return XML and XSLT is a goddamn super power. I adore it.

XSLT was cool.

XML needs another syntax that isn't so verbose. Sort of like how OWL has XML, Manchester, Functional, and Turtle syntaxes for the same data structures.

XSLT needs a Turtle-style syntax.

XML in general (the data structure, not the syntax) needs a Turtle-style syntax.

> but languished where it shined, as a markup language with an amazing transformation capability in XSLT

I choose to look at this a little differently.

An XML application using XSLT is so much better (faster load times, faster to write, easier to make correct) than a JavaScript application with a JSON api, that XML is basically a secret weapon.

I only care enough that it stays in browsers, but otherwise I'd prefer nobody know about it because it means less competition on things that matter (faster load times, faster to write, fewer bugs, etc). And I've got a half-baked JavaScript-based "renderer" I can finish in case some Google VP asshat goes looking for things to delete...

XSLT is just not a good language. Every single attempt of making XML executables (and there were many) failed badly, always for this one good reason.