src/StringType.php
public function getRealEncoding($encoding)
    {
        if (static::isEncodingSupported($encoding) === false) {
            throw new \Exception('Encoding is not supported: "' . $encoding . '"');
        }

        return static::supportedEncodings()[strtolower($encoding)];
    }
public function getRealEncoding($encoding)
    {
        if (static::isEncodingSupported($encoding) === false) {
            throw new \Exception('Encoding is not supported: "' . $encoding . '"');
        }

        return static::supportedEncodings()[strtolower($encoding)];
    }
Return the real encoding of the given alias

@param  string $encoding
@return string