texmath-0.10: tests/writers/mfracBalign16.tex
\begin{matrix}
{x - \frac{a}{b}x} \\
{x - \frac{1}{b}x} \\
{x - \frac{1}{2}x} \\
{x - \frac{1^{2}}{z}x} \\
{x - \frac{z}{1^{2}}x} \\
\end{matrix}
\begin{matrix}
{x - \frac{a}{b}x} \\
{x - \frac{1}{b}x} \\
{x - \frac{1}{2}x} \\
{x - \frac{1^{2}}{z}x} \\
{x - \frac{z}{1^{2}}x} \\
\end{matrix}