Since you are already using SafeHtmlBuilder, may save the hassle/load to use HTMLPanel. 
Also see org.zanata.webtrans.client.ui.TextContentsDisplay. You shouldn't need to use HighlightingLabel directly anymore. 
```
SafeHtmlBuilder builder = new SafeHtmlBuilder();
builder.appendHtmlConstant("<li>")
      .append(TextContentsDisplay.asSyntaxHighlight(targets).toSafeHtml())
      .appendHtmlConstant("</li>");
```