In the ideal world we would all be using s-expressions and Lisp, but now XML and JSON fill the need of language-independent data formats.

>Not trying to defend XSLT (which I find to be a mixed bag), but you're aware that it's precursor was DSSSL (Scheme), with pretty much a one-to-one correspondence of language constructs and symbol names, aren't you?

The mighty programmer James Clark wrote the de-facto reference SGML parser and DSSSL implementation, was technical lead of the XML working group, and also helped design and implement XSLT and XPath (not to mention expat, Trex / RELAX NG, etc)! It was totally flexible and incredibly powerful, but massively complicated, and you had to know scheme, which blew a lot of people's minds. But the major factor that killed SGML and DSSSL was the emergence of HTML, XML and XSLT, which were orders of magnitude simpler.

James Clark: http://www.jclark.com/ https://en.wikipedia.org/wiki/James_Clark_(programmer)

There's a wonderful DDJ interview with James Clark called "A Triumph of Simplicity: James Clark on Markup Languages and XML" where he explains how a standard has failed if everyone just uses the reference implementation, because the point of a standard is to be crisp and simple enough that many different implementations can interoperate perfectly.

A Triumph of Simplicity: James Clark on Markup Languages and XML:
http://www.drdobbs.com/a-triumph-of-simplicity-james-clark-o...

I think it's safe to say that SGML and DSSSL fell short of that sought-after simplicity, and XML and XSLT were the answer to that.

"The standard has to be sufficiently simple that it makes sense to have multiple implementations." -James Clark

My (completely imaginary) impression of the XSLT committee is that there must have been representatives of several different programming languages (Lisp, Prolog, C++, RPG, Brainfuck, etc) sitting around the conference table facing off with each other, and each managed to get a caricature of their language's cliche cool programming technique hammered into XSLT, but without the other context and support it needed to actually be useful. So nobody was happy!

Then Microsoft came out with MSXML, with an XSL processor that let you include <script> tags in your XSLT documents to do all kinds of magic stuff by dynamically accessing the DOM and performing arbitrary computation (in VBScript, JavaScript, C#, or any IScriptingEngine compatible language). Once you hit a wall with XSLT you could drop down to JavaScript and actually get some work done. But after you got used to manipulating the DOM in JavaScript with XPath, you being to wonder what you ever needed XSLT for in the first place, and why you don't just write a nice flexible XML transformation library in JavaScript, and forget about XSLT.

XSLT Stylesheet Scripting Using <msxsl:script>: https://docs.microsoft.com/en-us/dotnet/standard/data/xml/xs...

Excerpts from the DDJ interview (it's fascinating -- read the whole thing!):

>DDJ: You're well known for writing very good reference implementations for SGML and XML Standards. How important is it for these reference implementations to be good implementations as opposed to just something that works?

>JC: Having a reference implementation that's too good can actually be a negative in some ways.

>DDJ: Why is that?

>JC: Well, because it discourages other people from implementing it. If you've got a standard, and you have only one real implementation, then you might as well not have bothered having a standard. You could have just defined the language by its implementation. The point of standards is that you can have multiple implementations, and they can all interoperate.

>You want to make the standard sufficiently easy to implement so that it's not so much work to do an implementation that people are discouraged by the presence of a good reference implementation from doing their own implementation.

>DDJ: Is that necessarily a bad thing? If you have a single implementation that's good enough so that other people don't feel like they have to write another implementation, don't you achieve what you want with a standard in that all implementations — in this case, there's only one of them — work the same?

>JC: For any standard that's really useful, there are different kinds of usage scenarios and different classes of users, and you can't have one implementation that fits all. Take SGML, for example. Sometimes you want a really heavy-weight implementation that does validation and provides lots of information about a document. Sometimes you'd like a much lighter weight implementation that just runs as fast as possible, doesn't validate, and doesn't provide much information about a document apart from elements and attributes and data. But because it's so much work to write an SGML parser, you end up having one SGML parser that supports everything needed for a huge variety of applications, which makes it a lot more complicated. It would be much nicer if you had one SGML parser that is perfect for this application, and another SGML parser that is perfect for this other application. To make that possible, the standard has to be sufficiently simple that it makes sense to have multiple implementations.

>DDJ: Is there any markup software out there that you like to use and that you haven't written yourself?

>JC: The software I probably use most often that I haven't written myself is Microsoft's XML parser and XSLT implementation. Their current version does a pretty credible job of doing both XML and XSLT. It's remarkable, really. If you said, back when I was doing SGML and DSSSL, that one day, you'd find as a standard part of Windows this DLL that did pretty much the same thing as SGML and DSSSL, I'd think you were dreaming. That's one thing I feel very happy about, that this formerly niche thing is now available to everybody.