mfenced-08.test

<<< native
[ EDelimited
    "|"
    "|"
    [ Right
        (EArray
           [ AlignCenter ]
           [ [ [ EIdentifier "U" ] ] , [ [ EIdentifier "V" ] ] ])
    ]
, ESymbol Rel "="
, EDelimited
    "\8214"
    "\8214"
    [ Right
        (EArray
           [ AlignCenter ]
           [ [ [ EIdentifier "U" ] ] , [ [ EIdentifier "V" ] ] ])
    ]
]
>>> mml
<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mrow>
      <mo stretchy="true" form="prefix">|</mo>
      <mtable>
        <mtr>
          <mtd columnalign="center">
            <mi>U</mi>
          </mtd>
        </mtr>
        <mtr>
          <mtd columnalign="center">
            <mi>V</mi>
          </mtd>
        </mtr>
      </mtable>
      <mo stretchy="true" form="postfix">|</mo>
    </mrow>
    <mo>=</mo>
    <mrow>
      <mo stretchy="true" form="prefix">‖</mo>
      <mtable>
        <mtr>
          <mtd columnalign="center">
            <mi>U</mi>
          </mtd>
        </mtr>
        <mtr>
          <mtd columnalign="center">
            <mi>V</mi>
          </mtd>
        </mtr>
      </mtable>
      <mo stretchy="true" form="postfix">‖</mo>
    </mrow>
  </mrow>
</math>