How to extend a class from the library?

[eluser]Sinclair[/eluser]
Hi,

I need to validade International characters in the Form Validation Class.

I need to change the a class function from:

Code:

function alpha($str)
{
return ( ! preg_match("/^([a-z])+$/i", $str)) ? FALSE : TRUE;
}

to

Code:

function alpha($str)
{
return ( ! preg_match("/^([*A-Za-zá-úÁ=Ú.\s*])+$/i", $str)) ? FALSE : TRUE;
}

But if I do this. The next time I upgrade Codeigniter I broke it. How can I extend this class?

PS: Newbie in OOP.


Best Regards,