string-downcase

(string-downcase string-designator)

Returns a new string with every uppercase letter converted to lowercase; the original string is unchanged. The argument is a string designator, so a symbol, a keyword or a character is also accepted -- a symbol's name is used and a keyword's leading colon is dropped, so (string-downcase :FOO) returns "foo" and (string-downcase #\A) returns "a". Anything that is not one of those three types is an error. Case conversion is full-Unicode and identical on every backend: each character is folded with char-downcase, so (string-downcase "ÉΛΩ") returns "éλω". Because the fold is per character, the result always has the same length as the argument and no context-sensitive rule applies (a Greek final sigma is not special-cased).