chromium/content/test/data/accessibility/form-controls/img-map-pseudo.html

<source>
  <map name="map2" class="c1">
    <dfn class="c8"></dfn>
  </map>
</source>
<img usemap="#map2">
<style>
.c1:first-letter { content: "x"; }
.c8:after { content: "y";  }
.c1 { float: left;  }
</style>