docs: public String getSubSiteRoot(CmsObject cms, String rootPath) {
  
          CmsADEConfigData configData = lookupConfiguration(cms, rootPath);
          String basePath = configData.getBasePath();
          String siteRoot = OpenCms.getSiteManager().getSiteRoot(rootPath);
          if (siteRoot == null) {
              siteRoot = "";
          }
          if ((basePath == null) || !basePath.startsWith(siteRoot)) {
              // the subsite root should always be below the site root
              return siteRoot;
          } else {
              return basePath;
          }
      }