docs: public static void checkCharset(String accepts) throws IOException {
          if (accepts == null) {
              // ie7 does not send this header
              return;
          }
          // I've seen both "utf-8" and "UTF-8" -> test case-insensitive
          if (contains(accepts.toLowerCase(), Engine.ENCODING)) {
              return;
          }
          if (contains(accepts, "*")) {
              return;
          }
          throw new IOException(Engine.ENCODING + " encoding is not accepted: " + accepts);
      }