api/controllers/ApiRouter.php
public static function getOutputFormat()
    {
        preg_match(static::OUTPUT_FORMAT_PATTERN, uri_string(), $aMatches);
        $sFormat = !empty($aMatches[1]) ? strtoupper($aMatches[1]) : null;
        return static::isValidFormat($sFormat) ? $sFormat : static::DEFAULT_FORMAT;
    }
public static function getOutputFormat()
    {
        preg_match(static::OUTPUT_FORMAT_PATTERN, uri_string(), $aMatches);
        $sFormat = !empty($aMatches[1]) ? strtoupper($aMatches[1]) : null;
        return static::isValidFormat($sFormat) ? $sFormat : static::DEFAULT_FORMAT;
    }
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