declared empty elements (none, mprescripts, mspace)

$\frac{1^2}{\sqrt{a}}+\mathbf{b}+{}^{k}A^i{}^{\mathrm{kk}}{}_{\mathrm{ll}}X^{\mathrm{ii}}B$

empty table cells (<mtd/>)

$\begin{array}{cccccc}& & \text{a}& \text{b}& \text{c}& \\ \text{x}& (& 1& 2& 3& )\\ \text{y}& & 22& 33\\ \text{z}& & & 333\end{array}$

B.H.'s bin pow test

$${\left(x+y\right)}^2$$

Other stuff

$$\underset{0}{\overset{\infty }{\int }}\sqrt{\left\{\begin{array}{ccc}1& 2& 3\\ \to & \nwarrow & \downarrow \\ \alpha & \beta & \gamma \end{array}\right]}$$