code: public Content getNavLinkPrevious() {
          Content li;
          if (prev != null) {
              Content prevLink = getLink(new LinkInfoImpl(configuration,
                      LinkInfoImpl.Kind.CLASS, prev)
                      .label(prevclassLabel).strong(true));
              li = HtmlTree.LI(prevLink);
          }
          else
              li = HtmlTree.LI(prevclassLabel);
          return li;
      }
docs: Get link to previous class.
  
  @return a content tree for the previous class link