code: public static function underscore($value)
      {
          if (isset(self::$underscored[$value])) {
              return self::$underscored[$value];
          }
  
          return self::$underscored[$value] = str_replace('-', '_', self::decamelize($value));
      }
docs: Converts a camel case or dasherized string into a lower cased and underscored string.
  
  @param $value
  @return string