Simplified Common Lisp reference
Symbol class: Sequences (Lists, Strings) and Arrays
Symbol type: function
string-downcasestringstart(keyword)end(keyword) => string
Argument description:
string a string
start integer bouded by string length
end integer bouded by string length

STRING-DOWNCASE function converts string into its upcase reprezentation. returned. See also STRING-UPCASE, STRING-CAPITALIZE, CHAR-UPCASE and CHAR-DOWNCASE.

(string-downcase "SOME STRING") => "some string"
(string-downcase "SOME STRING" :start 2) => "SOme string"
(string-downcase "SOME STRING" :start 2 :end 8) => "SOme strING"
Function indexFull documentation for string-downcase (HyperSpec)