`base` (binary)

Base

AsciiMath

x_(y)

LaTeX

x_{y}

MathML

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mstyle displaystyle="true">
    <msub>
      <mi>x</mi>
      <mi>y</mi>
    </msub>
  </mstyle>
</math>

OMML

<m:oMathPara>
  <m:oMath>
    <m:sSub>
      <m:sSubPr>
        <m:ctrlPr>
          <w:rPr>
            <w:rFonts w:ascii="Cambria Math" w:hAnsi="Cambria Math"/>
            <w:i/>
          </w:rPr>
        </m:ctrlPr>
      </m:sSubPr>
      <m:e>
        <m:r>
          <m:t>x</m:t>
        </m:r>
      </m:e>
      <m:sub>
        <m:r>
          <m:t>y</m:t>
        </m:r>
      </m:sub>
    </m:sSub>
  </m:oMath>
</m:oMathPara>

UnicodeMath

x_(y)