The spec for this action:
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#G11.2111850
An example of a form using this action:
https://www2.illinois.gov/rev/forms/reg/Documents/reg-1-mr.pdf
get javaScript() {
    const javaScript = this._collectJavaScript();
    return shadow(
      this,
      "javaScript",
      javaScript ? [...javaScript.values()] : null
    );
  }
  get jsActions() {
    const javaScript = this._collectJavaScript();
    let actions = collectActions(
      this.xref,
      this._catDict,
      DocumentActionEventType
    );
    if (javaScript) {
      if (!actions) {
        actions = Object.create(null);
      }
      for (const [key, val] of javaScript) {
        if (key in actions) {
          actions[key].push(val);
        } else {
          actions[key] = [val];
        }
      }
    }
    return shadow(this, "jsActions", actions);
  }
  fontFallback(id, handler) {