Well, until you do need some metadata for that key-value pair. Which is why even in many JSON schemas it's pretty common to get something like { "key": "key", "value": "value", ... } (where ... is usually empty in practice).
The problem with MSBuild, for the most part, isn't XML - it's its own data model (which is not XDM, by the way).
My main point is in xml the closing tags are unnecessary, and you need an opening tag for every value where it’s obvious from nested context what that value is supposed to be. Xml is very redundant, there’s just all this zero entropy text everywhere which conveys no information. I disagree with your metadata in json example, why not just add more data to the value? The data model of msbuild is also annoying, but I’ve worked with some dotnet core projects now and using json as the project format definitely saves typing and actually allows you to intuit what a project is doing rather than just bombarding you with useless text.
And with respect to data and metadata, what you propose is not fundamentally different in terms of verbosity:
<foo metadata="bar">baz</foo>
{
"foo": {"value": "baz", "metadata": "bar"}
}
It’s just crazy to look at tbh, and it was annoying to type on my phone. I’m amazed people are still arguing in favor of it. In reality you just want the markup to transmit the most information in the least amount of bits. This is a measurable quantity and xml objectively sucks at it.
If that were the case, we'd be using binary serialization everywhere. But you yourself are making an argument that ease of writing matters. So does ease of reading. Overly verbose markup is a tax on both, but so is extreme brevity.
Anyway, this particular thread was a discussion to address a very specific point made in the article that overstated XML verbosity over JSON. I'm not actually arguing that XML is perfect, or even "good enough". Its syntax is overly verbose, and its data model has pointless distinctions and arbitrary restrictions. But it also had many good ideas, and it's unfortunate that those get ignored in the quest of simplifying everything - and then later, when the issues that were the original motivation for those ideas are rediscovered, that wheel gets reinvented in dozens of flawed and mutually incompatible ways.
Do you have difficulty in reading a large HTML document? That's as verbose and repetitive as XML but also usually filled with junk comments and malformed tags. If you don't find it hard, then why is XML different?
Scroll down and I think it shows it perfectly how (X|HT)ML tags are much simpler than JSON syntax once things get complex and nested. It's not that hard to define basic primitives like we do with HTML (which has dozens of tags) but XML also lets you define your own schema if necessary to make things more compact.
I understand the technicalities between HTML vs XML but I don't see how it makes any practical difference when you're editing a bunch of tags in a text file. It's the same thing. The structure looks identical. What is the actual issue that makes HTML easy but XML hard?