code: public void addClassContentTree(Content contentTree, Content classContentTree) {
          if (configuration.allowTag(HtmlTag.MAIN)) {
              mainTree.addContent(classContentTree);
              contentTree.addContent(mainTree);
          } else {
              contentTree.addContent(classContentTree);
          }
      }
docs: Add the class content tree.
  
  @param contentTree content tree to which the class content will be added
  @param classContentTree class content tree which will be added to the content tree