[Devasta]

Namespaces, schemas, custom elements, client side templating, XML has so much stuff that the web threw away, so now its forced to reinvent worse versions of it every few years, a shame.

Abandoning XML was the webs biggest mistake.

[giantrobot]

Whenever XML gets discussed here it's interesting to see what people complain about. In my completely unscientific assessment most things people hate(d) were the overwrought "Enterprise" uses/systems.

Very unfortunately for everyone XML came up at the same time as peak "Enterprise" moat building. No design pattern went unused everything was built with mind numbing "configuration". XML got used heavily in that space because it allowed massive "Enterprise Objects" (local branding varies) to be serialized in a way another system might have a chance to read.

Meanwhile the features you mention got thrown out with the bath water because everyone hated Enterprise style architectures. While I don't love, for instance, everything about XSLT it's built directly into browsers as native code. How many person hours, megabytes of JavaScript, and wasted CPU cycles have been spent reinventing client side templating using JSON? XSLT is already right there and will happily convert serialized data to your presentation format. You also get the ability to have comments in the data and a built in schema validation.

On my current project I'd much weather be emitting and consuming XML rather than JSON. But alas everyone hated Enterprise XML so we're stuck with JSON and the inability of some parsers to handle trailing commas and ambiguous definitions of numerics and not a comment to be found.

[Zamicol]

XML is oversized for the majority use case.

It's easier to extend a simple standard than to amputate a behemoth with unneeded appendages.

[recursive]

The problem with extending a standard is that there are so many ways to do it.