Well, that's the question.

It seems like every tool promotes its support of some XML based format and everyone is supposed to go all like "omg xml! yay!" yet I can't quite fanthom why is such a big deal.

I don't particulary consider XML a "pretty" schema to write your configuration files. It uses so many symbols, and not in a particularly "easy to look at" way.

What do you think?

There are so many existing tools and libraries for working with XML that you don't have to do much of your own implementation -- for most languages you can be writing or parsing XML files within a few minutes and only a few lines of code.

JSON or YAML are both becoming popular alternatives.

//EDIT: What SiCrane said -- XML was all the rage a couple of years back, and because of that there are loads of tools and libraries supporting it, but I'd agree with the feeling that JSON and YAML are now being preferred by most people.

I agree. The "XML rage" ended years ago. And that's a good thing. XML looks good on paper but it just doesn't work out well. The specification is ridiculously over-engineered and the signal/noise ratio is just stupidly low. But I think it is kind of ironic, that XML was supposed to be a back-end communication format that was never meant to be edited by humans, yet for some reason it became a general-purpose configuration file format. I guess one was needed more than the other

The year 2000 called, and they want their markup back

As above, I would've said that it's hype levels have died down a lot recently, with many people moving on to more sane options.

[edit]

To answer the question somewhat:

XML is a "mature technology" - it's standardized and flexible and there's a lot of tools support, and supporting tech like XSLT... which makes it an easy option to default to.

To get out my nasty feelings:

It is just plain bad though. I feel wrong when I touch it.

When using all of it's features, it completely fails as a human readable format... and if it's not going to be human readable, then using UTF8/etc to store arbitrary data is just horribly inefficient.

Aww man. Well, in my defense, 2/3 of the tools you find have some sort of XML file for configurations/formats/serialization/etc (say, build tools, or formats like collada).

Its just that it looked so ugly to think "Oh, I see what problem this is solving!"

I'm glad its been phased out. I knew a bit about JSON but YAML looks much, much better.

From a professional standpoint, a lot of businesses still use xml as their data markup language. I think that carries over into the gaming industry as well simply because of the sheer number of objects that support it.

YAML is taking off? I have yet to see anything use it. JSON though, yes, it seems that lately everybody and their dogs are using JSON now. Probably because we're in full HTML5 mode, and JSON data is valid javascript, so using it is a non-brainer as you don't even need a parser (I wonder if anybody understands the implications of loading data as code though).

Personally, I prefer INI files anyway (well, INI-like at least). Yeah, call me old-fashioned, but they're a lot easier to deal with. XML is good when you need tree-style nesting, but most of the time you don't, really (and even then, those using XML more often than not abuse it resulting in ridiculously complex formats for no real reason).