PrinceXML

HTML

<span title="C" class="nested">
  <span title="B" class="nested">
    <span title="A">Text 1.</span>
  </span>
</span>
<span title="F" class="nested">
  <span title="E" class="nested">
    <span title="D">Text 2.</span>
  </span>
</span>

CSS

span {
   display: inline-block;
}
span::before {
  display: block;
  content: attr(title);
  text-align: left;
  border: 1px solid red;
}
span.nested::before {
  content: attr(title);
  display: inline-block;
  width: 100%;
  text-align: right;
}