LayoutTests/fast/text/word-spacing-rtl.html

<style>
div { 
  font-family: Ahem;
  font-size: 20px;
  width: 200px;
  color: green;
}
</style>
<div style="direction: ltr; word-spacing: 20px;">X X X</div>
<div style="direction: rtl; word-spacing: 20px;">X X X</div>

<div style="direction: ltr; word-spacing: -20px;">X X X</div>
<div style="direction: rtl; word-spacing: -20px;">X X X</div>