code: function getDefaultValue(customSelect) {
      var val = customSelect.getAttribute('value');
      if (val === null) {
        return '';
      }
      var firstChar = val[0];
      if (firstChar === undefined) {
        return '';
      } else if (firstChar === '[') {
        return JSON.parse(val);
      }
      return val;
    }
docs: Get default value from value="" attribute
  which might be a string representing a single selected option value
  or a JSON array representing selected options in multiple select
  
  This attribute has highest priority over aria-selected which will be updated in syncUI()
  If value is empty string or no value attribute found then 1st option is selected
  
  @param customSelect
  @returns {String|Array}