The __ctype_tolower_loc
function shall return a pointer into an array
characters in the current locale that contains lower case equivalents for each
character in the current character set. The array shall contain a total of 384
characters, and can be indexed with any signed or unsigned char (i.e. with an
index value between -128 and 255). If the application is multithreaded, the
array shall be local to the current thread.
This interface is not in the source standard; it is only in the binary standard.