* @throws NullPointerException if {@code element} is null and this implementation does not permit
   *     null elements. Note that if {@code occurrences} is zero, the implementation may opt to
   *     return normally.
   */
  @CanIgnoreReturnValue
  int add(@ParametricNullness E element, int occurrences);

  /**
   * Adds a single occurrence of the specified element to this multiset.
   *

  /**
   * The HTTP <a href="https://github.com/WICG/nav-speculation/blob/main/opt-in.md">{@code
   * Supports-Loading-Mode}</a> header field name. This can be used to specify, for example, <a
   * href="https://developer.chrome.com/docs/privacy-sandbox/fenced-frame/#server-opt-in">fenced
   * frames</a>.
   *
   * @since 32.0.0
   */