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
elementData.userValue = event.detail.value || "";
              storage.setValue(id, { value: elementData.userValue.toString() });
              if (!elementData.formattedValue) {
                event.target.value = elementData.userValue;
              }
            },
            valueAsString(event) {
              elementData.formattedValue = event.detail.valueAsString || "";
              if (event.target !== document.activeElement) {
                
                event.target.value = elementData.formattedValue;
              }
              storage.setValue(id, {
                formattedValue: elementData.formattedValue,
              });
            },
            selRange(event) {