Declaring Constants in PDO

[Ambrish]

Hi,

I was going through the following link:
http://in.php.net/manual/en/internals2.pdo.constants.php

Related to this link I have following questions:
1. If I want to add another constant, then who can I do it (That constant might be database specific)?
2. Is there any standard while declaring these constants? Like the number range for PDO constants which is reserved by PDO and we have to use numbers out side this range for database specific constants.

Thanks in advance.

Regards,
Ambrish Bhargava