CodeIgniter's valid_email() vs PHP filter

I noticed that CodeIgniter has implemented the valid_email() function, in which they are using preg_match.

Why d开发者_如何转开发idn't they use PHP's filter with FILTER_VALIDATE_EMAIL?

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filter_var() requires PHP 5.2 or greater. CodeIgniter runs on PHP 5.1.6 or greater. The CodeIgniter developers can't guarantee that people will have access to the filter_var() function.