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
while (selectElement.length !== 0) {
              selectElement.remove(0);
            }
            storage.setValue(id, { value: null, items: [] });
          },
          insert(event) {
            const { index, displayValue, exportValue } = event.detail.insert;
            const optionElement = document.createElement("option");
            optionElement.textContent = displayValue;
            optionElement.value = exportValue;
            selectElement.insertBefore(
              optionElement,
              selectElement.children[index]
            );
            storage.setValue(id, {
              value: getValue(event,  true),
              items: getItems(event),
            });
          },
          items(event) {