Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/TextData.php
public static function VALUE($value = '')
    {
        $value = Functions::flattenSingleValue($value);

        if (!is_numeric($value)) {
            $numberValue = str_replace(
                StringHelper::getThousandsSeparator(),
                '',
                trim($value, " \t\n\r\0\x0B" . StringHelper::getCurrencyCode())
            );
            if (is_numeric($numberValue)) {
                return (float) $numberValue;
            }

            $dateSetting = Functions::getReturnDateType();
            Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);

            if (strpos($value, ':') !== false) {
                $timeValue = DateTime::TIMEVALUE($value);
                if ($timeValue !== Functions::VALUE()) {
                    Functions::setReturnDateType($dateSetting);

                    return $timeValue;
                }
            }
            $dateValue = DateTime::DATEVALUE($value);
            if ($dateValue !== Functions::VALUE()) {
                Functions::setReturnDateType($dateSetting);

                return $dateValue;
            }
            Functions::setReturnDateType($dateSetting);

            return Functions::VALUE();
        }

        return (float) $value;
    }
public static function VALUE($value = '')
    {
        $value = Functions::flattenSingleValue($value);

        if (!is_numeric($value)) {
            $numberValue = str_replace(
                StringHelper::getThousandsSeparator(),
                '',
                trim($value, " \t\n\r\0\x0B" . StringHelper::getCurrencyCode())
            );
            if (is_numeric($numberValue)) {
                return (float) $numberValue;
            }

            $dateSetting = Functions::getReturnDateType();
            Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);

            if (strpos($value, ':') !== false) {
                $timeValue = DateTime::TIMEVALUE($value);
                if ($timeValue !== Functions::VALUE()) {
                    Functions::setReturnDateType($dateSetting);

                    return $timeValue;
                }
            }
            $dateValue = DateTime::DATEVALUE($value);
            if ($dateValue !== Functions::VALUE()) {
                Functions::setReturnDateType($dateSetting);

                return $dateValue;
            }
            Functions::setReturnDateType($dateSetting);

            return Functions::VALUE();
        }

        return (float) $value;
    }
VALUE.

@param mixed $value Value to check

@return bool