Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Functions.php
public static function isNumber($value = null)
    {
        $value = self::flattenSingleValue($value);

        if (is_string($value)) {
            return false;
        }

        return is_numeric($value);
    }
public static function isNumber($value = null)
    {
        $value = self::flattenSingleValue($value);

        if (is_string($value)) {
            return false;
        }

        return is_numeric($value);
    }
IS_NUMBER.

@param mixed $value Value to check

@return bool