this is a function that
Convert uppercase letter to lowercase
Converts c to its lowercase equivalent if c is an uppercase letter and has a lowercase equivalent. If no such conversion is possible, the value returned is
c unchanged.
Notice that what is considered a letter may depend on the locale being used; In the default
"C" locale, an uppercase letter is any of: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z, which translate respectively to:
a b c d e f g h i j k l m n o p q r s t u v w x y z.