Display:

$\underset{\⏟}{x+y+z}\text{\ versus\ }\underset{\⏟}{x+y+z}$

Source:

<mrow>
     <munder accentunder="true">
          <mrow>
               <mi> x </mi>
               <mo> + </mo>
               <mi> y </mi>
               <mo> + </mo>
               <mi> z </mi>
          </mrow>
          <mo> &UnderBrace; </mo>
     </munder>
     <mtext>&nbsp;versus&nbsp;</mtext>
     <munder accentunder="false">
          <mrow>
               <mi> x </mi>
               <mo> + </mo>
               <mi> y </mi>
               <mo> + </mo>
               <mi> z </mi>
          </mrow>
          <mo> &UnderBrace; </mo>
     </munder>
</mrow>