[xorcist]

But your XML document also has syntax! You just pushed it up one level of abstraction.

Your proto-math XML dialect of:

  <subtract><minuend>5</minuend><subtrahend>3</subtrahend></subtract>

instead of:

  5-3

still has higher level syntax. What does:

  <subtract><minuend>5</minuend><subtrahend>i</subtrahend></subtract>

mean? Is it a syntax error? Or does it subtract imaginary numbers? What about exponential notation?

You will have a parser anyway, whether you like it or not. Given that, perhaps "5-3" is the simpler notation after all, even though it requires a specialized (albeit trivial) parser to be carried along with it.