Description:
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There is a problem in the manual (german translation) which you can find here:

http://de3.php.net/manual/de/function.mysql-real-escape-string.php

See the section called "Beispiel 2".
See the definition of a function called "quote_smart()".

In the body you will find "!is_int($value)", it should be
"!is_numeric($value)" as you can read it in the english original (http://de3.php.net/manual/en/function.mysql-real-escape-string.php)