See the "Notes" section further down the page, which says:

    Note: As of PHP 5.3.0, the regex extension is deprecated 
    in favor of the PCRE extension. Calling this function 
    will issue an E_DEPRECATED notice. See the list of 
    differences for help on converting to PCRE.
    
    Tip: preg_split(), which uses a Perl-compatible regular 
    expression syntax, is often a faster alternative to 
    split(). If you don't require the power of regular 
    expressions, it is faster to use explode(), which doesn't 
    incur the overhead of the regular expression engine.
    
    Tip: For users looking for a way to emulate Perl's 
    @chars = split('', $str) behaviour, please see the 
    examples for preg_split() or str_split().