MathML Fundamentals - Making Sub-Expressions Invisible mphantom

The mphantom element renders invisibly, but with the same size and other dimensions, including baseline position, that its contents would have if they were rendered normally. Mphantom can be used to align parts of an expression by invisibly duplicating sub-expressions. MathML Fundamentals

MPhantom Test x + y + z x + y + z

MathML

<math mathsize="70">
    <mspace linebreak="newline" indentalign="center"></mspace>
    <mtext style="border:1px;">MPhantom Test</mtext>
    <mspace linebreak="newline" indentalign="center"></mspace>
    <mfrac>
        <mrow>
            <mi>x</mi>
            <mo>+</mo>
            <mi>y</mi>
            <mo>+</mo>
            <mi>z</mi>
        </mrow>
        <mrow>
            <mi>x</mi>
            <mphantom>
                <mo>+</mo>
                <mi>y</mi>
            </mphantom>
            <mo>+</mo>
            <mi>z</mi>
        </mrow>
    </mfrac>
</math>