Maybe I just like the idea of a closing tag being very specific about what it is that is being closed (?).

That's kind of what I was getting at with the mental scoping.

My peeve with json is that… it doesn’t properly distinguish between strings that happen to be a number and “numbers"

Is that implementation-specific, or did they bake JavaScript type awfulness into the standard? Or are numbers even supported - it's all binary at the machine level, so I could see an argument that every (tree) node value should be a string, and actual types should be left to higher levels of abstraction.

I actually don’t like the attributes in xml, I think it would be better if it was mandatory that they were also just more tagged elements inside the others, and that the “validity” of a piece of xml being a certain object would depend entirely on parsing correctly or not.

I particularly hate the idea of attributes in svg, and even more particularly the way they defined paths.

I agree. The latter isn't even a matter of taste, they're just implementing their own homebrew syntax inside an attribute, circumventing the actual format, WTF.