public static function isValidISBN10($isbn)
    {
        $isbn = self::normalizeISBN($isbn);
        if (strlen($isbn) != 10) {
            return false;
        }
        return substr($isbn, 9) == self::getISBN10CheckDigit(substr($isbn, 0, 9));
    }
public static function isValidISBN10($isbn)
    {
        $isbn = self::normalizeISBN($isbn);
        if (strlen($isbn) != 10) {
            return false;
        }
        return substr($isbn, 9) == self::getISBN10CheckDigit(substr($isbn, 0, 9));
    }
public static function isValidISBN10 ( $ isbn ) { $ isbn = self :: normalizeISBN ( $ isbn ) ; if ( strlen ( $ isbn ) != 10 ) { return false ; } return substr ( $ isbn , 9 ) == self :: getISBN10CheckDigit ( substr ( $ isbn , 0 , 9 ) ) ; }
Is the provided ISBN-10 valid?

@param string $isbn The ISBN-10 to test.

@return boolean
Is the provided ISBN - 10 valid?