An mspace empty element represents a blank space of any desired size, as set by its attributes. It can also be used to make linebreaking suggestions to a visual renderer. MathML Fundamentals
<math>
<mspace linebreak="newline" indentalign="center"></mspace>
<mtext style="border:1px;" mathsize="50">Mspace - width, height, depth, indentalign</mtext>
<mspace linebreak="newline" indentalign="center"></mspace>
<mrow style="border:1px">
<mtext>aaa</mtext>
<mspace style="border:1px" width="50" height="10"></mspace>
<msqrt style="border:1px">
<mrow style="border:1px">
<mi style="border:1px">aagg</mi>
<mo>+</mo>
<mspace style="border:1px" width="10" height="100"></mspace>
<mi style="border:1px">ABC</mi>
<mspace style="border:1px" width="10" height="0" depth="20"></mspace>
<mi style="border:1px">ABC</mi>
</mrow>
</msqrt>
</mrow>
</math>