code: public void setPathPrefix(String prefix) {
      if (prefix.startsWith("/") || prefix.endsWith("/")) {
        throw new IllegalArgumentException("Prefix must not start or end with '/'.");
      }
      pathPrefix = (prefix.length() == 0) ? prefix : (prefix + "/");
    }
docs: Configures a prefix which is prepended to all asset paths prior to loading. Android assets are
  normally loaded via the Android AssetManager, which expects all assets to be in the {@code
  assets} directory. This prefix is thus inserted between {@code assets} and the path supplied
  to any of the various {@code get} methods.