code: function controls(data, options) {
      return data.reduce(function reduce(controls, item, n) {
        return controls + options.fn({
          panel: 'panel' + n,
          checked: !n ? ' checked' : ''
        });
      }, '');
    }
docs: Handblebar helper to generate the panel controls,
  both the radio buttons as well as the arrow labels.
  
  @param {Object} data Provided to the iterator.
  @param {Object} options Optional.
  @return {String} Generated template
  @api private