<!DOCTYPE html>
<html>
<math>
<mrow>
<mn>1</mn>
<mo>⁡<!-- FUNCTION APPLICATION --></mo>
<mn>2</mn>
<mo>⁢<!-- INVISIBLE TIMES --></mo>
<mn>3</mn>
<mo>⁣<!-- INVISIBLE SEPARATOR --></mo>
<mn>4</mn>
<mo>⁤<!-- INVISIBLE PLUS --></mo>
<mn>5</mn>
<!-- Hack. The invisible operators may not belong to the same font as
the numbers, so they may have different heights. The mspace
compensates for this by ensuring the height of the mrow does not
depend on character height -->
<mspace height="2em" width="0.1em"></mspace>
</mrow>
</math>
<p>
<!-- Should be invisible -->
<math>
<mo style="background: red; color: blue;">⁡</mo>
</math>
</html>