Returns string with all alphabetic characters converted to lowercase.
Note that 'alphabetic' is determined by the current locale. This means that in i.e. the default "C" locale, characters such as umlaut-A (Ä) will not be converted.
Megjegyzés: Ez a függvény "binary-safe", azaz helyesen kezeli a 127-es ASCII kód feletti karaktereket is.
See also strtoupper(), ucfirst(), ucwords() and mb_strtolower().