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
if (!event.target.multiple) {
        return options.selectedIndex === -1
          ? null
          : options[options.selectedIndex][name];
      }
      return Array.prototype.filter
        .call(options, option => option.selected)
        .map(option => option[name]);
    };
    const getItems = event => {
      const options = event.target.options;
      return Array.prototype.map.call(options, option => {
        return { displayValue: option.textContent, exportValue: option.value };
      });
    };
    if (this.enableScripting && this.hasJSActions) {
      selectElement.addEventListener("updatefromsandbox", jsEvent => {
        const actions = {
          value(event) {
            const options = selectElement.options;
            const value = event.detail.value;
            const values = new Set(Array.isArray(value) ? value : [value]);
            Array.prototype.forEach.call(options, option => {
              option.selected = values.has(option.value);
            });
            storage.setValue(id, {
              value: getValue(event,  true),
            });
          },
          multipleSelection(event) {