Tagged Equation Test

A tagged single equation produced by \tag{} is wrapped by MathJax in an mtable with a single mlabeledtr. It should stay on one horizontal line, not collapse into a vertical stack.

\begin{matrix} (⋆) & a = b + c \end{matrix}

A genuine multi-row aligned system uses several mtr rows and must be preserved as an aligned environment.

\begin{array}{rcl} x & = & y \\ u & = & v \end{array}