roundcubemail/program/lib/Roundcube/rcube_mime.php
public static function decode_header($input, $fallback = null)
    {
        $str = self::decode_mime_string((string)$input, $fallback);

        return $str;
    }
public static function decode_header($input, $fallback = null)
    {
        $str = self::decode_mime_string((string)$input, $fallback);

        return $str;
    }
public static function decode_header ( $ input , $ fallback = null ) { $ str = self :: decode_mime_string ( ( string ) $ input , $ fallback ) ; return $ str ; }
Decode a message header value

@param string  $input    Header value
@param string  $fallback Fallback charset if none specified

@return string Decoded string
Decode a message header value