How to evaluate powers of powers (i.e. $2^3^4$) in absence of parentheses? If you look at $2^{3^4}$, what is the expected result? Should it be read as $2^{(3^4)}$ or $(2^3)^4$? Normally I would use parentheses to make the meaning clear, but if none are shown, what would you expect?
(In this case, the formatting gives a hint, because I can either enter $2^{3^4}$ or ${2^3}^4$. If I omit braces in the MathML expression, the output is shown as $2^3^4$. Just suppose all three numbers were displayed in the same size, and the same vertical offset between 2, 3 and 3, 4.)

In the same way that any expressions in brackets inside other brackets are done before the rest of the things in the brackets, I'd say that one works from the top down in such a case.
i.e. because we do $(a*d)$ first in$((a*b)*c)*d$, I'd imagine it'd be the expected thing to do $x^{(y^z)}$
