--- downcase
--- downcase!

    ʸΥե٥åʸ򤹤٤ƾʸ֤ޤ

    downcase ѹʸ֤ޤ
    downcase!  self ѹ֤ޤִ
    ʤä nil ֤ޤ

    $KCODE ŬڤꤵƤʤСɤΰѴ
    Ƥޤޤ(ϡShiftJIS ɤǵޤ)
    դˡ$KCODE ꤷƤޥХʸΥե٥å
    Ͻޤ

        # -*- Coding: shift_jis -*-
        $KCODE ='n'
        puts "".downcase # => 

    upcase, swapcase,
    capitalize ⻲ȤƤ

