code: function _attachChangeAndDefaultFileEvent(form_id) {
          var _this = this;
  
          var elements = this._collection[form_id].getInputs();
          [].forEach.call(elements, function (form_control) {
  
              _this.__attachSingleChangeEvent(form_id, form_control);
              _this.__observeSingleValueChange(form_id, form_control);
  
              // set default file input value
              if (form_control.type === 'file' && form_control.hasAttribute('value')) {
                  var url = form_control.getAttribute('value');
                  if (url !== '') {
                      _this.setFileFromUrl(form_id, form_control.name, url);
                  }
              }
          });
      }
docs: Update FormData when user changed input's value
  or when value changed from script
  
  Also init default value for File inputs
  
  @param {string} form_id
  
  @private