>>10
The standard of having library support in just about every language out there.
Yes, XML does looks a bit verbose for the toy examples you provide, and the error detection falls a bit short when you just nest identical tags. It should be used for storing documents and hierarchical data, especially if it should be portable amongst applications.
Python is relevant to my interests too, and as I said, I wouldn't use XML for just communicating with client Javascript.
>>13,14
Sure, that looks halfway decent, except for maybe the STYLE= thing. Significant whitespace doesn't play very well with PHP style templates though.
Are S-expressions actually used for much outside of the Lisp world? I have the distinct impression that they aren't.