code: function(element, key) {
          var value = element.data((this.keyName + '-' + key).toLowerCase());
  
          if ($.type(value) === 'undefined') {
              value = this.options[key];
          }
  
          return value;
      }
docs: Read a class option from a data attribute.
  If no attribute exists, return the option value.
  
  @param {jQuery} element
  @param {String} key
  @returns {*}