rec-selector2

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <csymbol cd="linalg1">matrix_selector</csymbol>
    <cn>3</cn>
    <cn>2</cn>
    <semantics>
      <ci>A</ci>
      <annotation-xml cd="mathmltypes" name="type" encoding="MathML-Content">
        <ci>matrix</ci>
      </annotation-xml>
    </semantics>
  </apply>
</math>

Author: MathML 2 Recomendation