> The second one is a number

This would've been useful if you knew what kind of number it was...

As for what goes into separate elements and what goes into attributes: a typical answer to this is that simple types (as per XSL) go into attributes, complex types go into elements.

Compare this to JSON's screwed-up definition of "hash-tables" (the things in curly braces) which doesn't require that "keys" be unique.

XML wasn't perfect. But JSON isn't really better. It sucks in a slightly different way because people keep inventing these formats w/o much thinking, and once discover problems, don't fix them.