src/Str.php
public static function lower($input, $encoding = self::DEFAULT_ENCODING)
    {
        return function_exists('mb_strtolower')
            ? mb_strtolower($input, $encoding)
            : strtolower($input);
    }
public static function lower($input, $encoding = self::DEFAULT_ENCODING)
    {
        return function_exists('mb_strtolower')
            ? mb_strtolower($input, $encoding)
            : strtolower($input);
    }
public static function lower ( $ input , $ encoding = self :: DEFAULT_ENCODING ) { return function_exists ( 'mb_strtolower' ) ? mb_strtolower ( $ input , $ encoding ) : strtolower ( $ input ) ; }
Returns a lowercased string.

Returns a lowercased string. The $encoding parameter is used to determine the input string encoding
and thus use the proper method. The functions uses mb_strtolower if present and falls back to strtolower.

@author FuelPHP (http://fuelphp.com)

@param string $input    The input string
@param string $encoding The encoding of the input string

@return string The lowercased string
Returns a lowercased string .