I am curious:
I've never used an outliner,
I don't have a Macintosh,
so can anybody try and explain to me how
te make outlines?

I am interested in this because I want to know
what the best way is to type XML.

So how does one add a child, how to navigate,
etc.

I see that most outliners use a triangle or
a +/- to display outlines, but how about that
block-formating that XML-spy uses?

I tried to put a little bit at http://a-sharp.com/acta/ but it doesn't go into the nitty-gritty of keyboard equivalents (e.g. Enter creates a new topic) and how you can grab a topic by its triangle to move around.

MORE, ThinkTank, and Acta (and Frontier) are all pretty similar in this regard, though they use different keyboard equivalents.