W3C MathML TestSuite: Version 3: Test-case mlabeledtrAside2

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\begin{matrix} 1st & \frac{a + 1}{2} & b & c & d & e \\ 2nd & x & \frac{2}{3} y + 5 & z & d & e \\ 3rd & 1 & 2 & 5 & d & e \end{matrix}