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
this._actions = createActionsMap(data.actions);
    this._browseForFileToSubmit = data.browseForFileToSubmit || null;
    this._buttonCaption = null;
    this._buttonIcon = null;
    this._children = null;
    this._currentValueIndices = data.currentValueIndices || 0;
    this._document = data.doc;
    this._fieldPath = data.fieldPath;
    this._fillColor = data.fillColor || ["T"];
    this._isChoice = Array.isArray(data.items);
    this._items = data.items || [];
    this._page = data.page || 0;
    this._strokeColor = data.strokeColor || ["G", 0];
    this._textColor = data.textColor || ["G", 0];
    this._value = data.value || "";
    this._kidIds = data.kidIds || null;
    this._fieldType = getFieldType(this._actions);
    this._siblings = data.siblings || null;
    this._globalEval = data.globalEval;
    this._appObjects = data.appObjects;
    this.valueAsString = data.valueAsString || this._value;
  }
  get currentValueIndices() {
    if (!this._isChoice) {
      return 0;
    }
    return this._currentValueIndices;
  }
  set currentValueIndices(indices) {