[PHP-DOC] String length property (avoid strlen)

[Werner Beroux]

I found an interesting note that I quote here:
"[4]  [...] be sure to remember that PHP holds the length property of each 
string, and that it shouldn't be calculated with strlen()."
                --  
http://cvs.php.net/viewvc.cgi/php-src/CODING_STANDARDS?view=co

Now I found nowhere anything else about this and strlen is described 
everywhere. Is it some kind of new feature of PHP6?

Werner