Html

[EnSanity]

I'm currently teaching myself HTML in order to later learn XML. Is HTML useful knowledge in the game industry, and if not, is XML? Also, how through does my knowledge of HTML have to be to begin learning XML?

[yaustar]

Is HTML useful knowledge in the game industry

Not really.

and if not, is XML?

It is more commonly used for data.

Also, how through does my knowledge of HTML have to be to begin learning XML?

Not very. HTML is a small markup language and shouldn't take more then a couple of days to learn. Learning HTML with CSS is more beneficial if you are planning to make web pages.

[Gshonk]

I actually use XML extensively (haha see what I did there (if not google XML)) in my data driven programs. But it is super simple to learn.

[wobalisk]

I would agree with yaustar with css and html and a graphics edditing program its easy to make an ok webpage. If you want to do more complecated stuff php is good though

[Adrir]

I like using simple asciii-based ini files for defining stuff in the game, since it takes about a day to write a decent parser and code-generator so I can give the designers an easy UI to create new space ships and statistics and everything.