When we aim a hint at some expanded tokens, we're only willing to attach it
to spelled tokens that exactly corresponde.
int zoom(int x, int y, int z);
int dummy = zoom(NUMBERS);
Here we want to place a hint "x:" on the expanded "1", but we shouldn't
be willing to place it on NUMBERS, because it doesn't *exactly*
correspond (it has more tokens).
Fortunately we don't even have to implement this algorithm from scratch,
TokenBuffer has it.