docs: public static boolean isPackageOrClassName(String s) {
          if (S.blank(s)) {
              return false;
          }
          S.List parts = S.fastSplit(s, ".");
          if (parts.size() < 2) {
              return false;
          }
          for (String part: parts) {
              if (!Character.isJavaIdentifierStart(part.charAt(0))) {
                  return false;
              }
              for (int i = 1, len = part.length(); i < len; ++i) {
                  if (!Character.isJavaIdentifierPart(part.charAt(i))) {
                      return false;
                  }
              }
          }
          return true;
      }