<!doctype html>
<html>
  <head>
    <title>dir mo</title>
    <meta charset="utf-8"/>
  </head>
  <body>

    <!-- This checks prefix form in RTL mode. -->
    _<math dir="rtl"><mo>+</mo><mi>x</mi></math>_

    <br/>

    <!-- This checks leading and trailing spaces in RTL mode. -->
    _<math dir="rtl"><mi>x</mi><mo lspace="1em" rspace="2em">+</mo><mi>y</mi></math>_

  </body>
</html>