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

        return is_string($value) && !self::isError($value);
    }
public static function isText($value = null)
    {
        $value = self::flattenSingleValue($value);

        return is_string($value) && !self::isError($value);
    }
IS_TEXT.

@param mixed $value Value to check

@return bool