constructor(parent) {
    super();
    const { map, hash, transfer } = parent.serializable;
    // Create a *copy* of the data, since Objects are passed by reference in JS.
    const clone = structuredClone(map, transfer ? { transfer } : null);

    this.#serializable = { map: clone, hash, transfer };
  }
A special `AnnotationStorage` for use during printing, where the serializable
data is *frozen* upon initialization, to prevent scripting from modifying its
contents. (Necessary since printing is triggered synchronously in browsers.)